SPDX-License-Identifier: GPL-2.0+

#

(C) Copyright 2000 - 2013

Wolfgang Denk, DENX Software Engineering, wd@denx.de.

Summary:

This directory contains the source code for U-Boot, a boot loader for Embedded boards based on PowerPC, ARM, MIPS and several other processors, which can be installed in a boot ROM and used to initialize and test the hardware or to download and run application code.

The development of U-Boot is closely related to Linux: some parts of the source code originate in the Linux source tree, we have some header files in common, and special provision has been made to support booting of Linux images.

Some attention has been paid to make this software easily configurable and extendable. For instance, all monitor commands are implemented with the same call interface, so that it’s very easy to add new commands. Also, instead of permanently adding rarely used code (for instance hardware test utilities) to the monitor, you can load and run it dynamically.

Status:

In general, all boards for which a configuration option exists in the Makefile have been tested to some extent and can be considered “working”. In fact, many of them are used in production systems.

In case of problems see the CHANGELOG file to find out who contributed the specific port. In addition, there are various MAINTAINERS files scattered throughout the U-Boot source identifying the people or companies responsible for various boards and subsystems.

Note: As of August, 2010, there is no longer a CHANGELOG file in the actual U-Boot source tree; however, it can be created dynamically from the Git log using:

make CHANGELOG

Where to get help:

In case you have questions about, problems with or contributions for U-Boot, you should send a message to the U-Boot mailing list at u-boot@lists.denx.de. There is also an archive of previous traffic on the mailing list - please search the archive before asking FAQ’s. Please see https://lists.denx.de/pipermail/u-boot and https://marc.info/?l=u-boot

Where to get source code:

The U-Boot source code is maintained in the Git repository at https://source.denx.de/u-boot/u-boot.git ; you can browse it online at https://source.denx.de/u-boot/u-boot

The “Tags” links on this page allow you to download tarballs of any version you might be interested in. Official releases are also available from the DENX file server through HTTPS or FTP. https://ftp.denx.de/pub/u-boot/ ftp://ftp.denx.de/pub/u-boot/

Where we come from:

• start from 8xxrom sources
• create PPCBoot project (https://sourceforge.net/projects/ppcboot)
• clean up code
• make it easier to add custom boards
• make it possible to add other [PowerPC] CPUs
• extend functions, especially:
  • Provide extended interface to Linux boot loader
  • S-Record download
  • network boot
  • ATA disk / SCSI … boot
• create ARMBoot project (https://sourceforge.net/projects/armboot)
• add other CPU families (starting with ARM)
• create U-Boot project (https://sourceforge.net/projects/u-boot)
• current project page: see https://www.denx.de/wiki/U-Boot

Names and Spelling:

The “official” name of this project is “Das U-Boot”. The spelling “U-Boot” shall be used in all written text (documentation, comments in source files etc.). Example:

This is the README file for the U-Boot project.

File names etc. shall be based on the string “u-boot”. Examples:

include/asm-ppc/u-boot.h

#include <asm/u-boot.h>

Variable names, preprocessor constants etc. shall be either based on the string “u_boot” or on “U_BOOT”. Example:

U_BOOT_VERSION        u_boot_logo
IH_OS_U_BOOT        u_boot_hush_start

Versioning:

Starting with the release in October 2008, the names of the releases were changed from numerical release numbers without deeper meaning into a time stamp based numbering. Regular releases are identified by names consisting of the calendar year and month of the release date. Additional fields (if present) indicate release candidates or bug fix releases in “stable” maintenance trees.

Examples: U-Boot v2009.11 - Release November 2009 U-Boot v2009.11.1 - Release 1 in version November 2009 stable tree U-Boot v2010.09-rc1 - Release candidate 1 for September 2010 release

Directory Hierarchy:

/arch Architecture-specific files /arc Files generic to ARC architecture /arm Files generic to ARM architecture /m68k Files generic to m68k architecture /microblaze Files generic to microblaze architecture /mips Files generic to MIPS architecture /nios2 Files generic to Altera NIOS2 architecture /powerpc Files generic to PowerPC architecture /riscv Files generic to RISC-V architecture /sandbox Files generic to HW-independent “sandbox” /sh Files generic to SH architecture /x86 Files generic to x86 architecture /xtensa Files generic to Xtensa architecture /api Machine/arch-independent API for external apps /board Board-dependent files /boot Support for images and booting /cmd U-Boot commands functions /common Misc architecture-independent functions /configs Board default configuration files /disk Code for disk drive partition handling /doc Documentation (a mix of ReST and READMEs) /drivers Device drivers /dts Makefile for building internal U-Boot fdt. /env Environment support /examples Example code for standalone applications, etc. /fs Filesystem code (cramfs, ext2, jffs2, etc.) /include Header Files /lib Library routines generic to all architectures /Licenses Various license files /net Networking code /post Power On Self Test /scripts Various build scripts and Makefiles /test Various unit test files /tools Tools to build and sign FIT images, etc.

Software Configuration:

Selection of Processor Architecture and Board Type:

For all supported boards there are ready-to-use default configurations available; just type “make _defconfig”.

Example: For a TQM823L module type:

cd u-boot
make TQM823L_defconfig

Note: If you’re looking for the default configuration file for a board you’re sure used to be there but is now missing, check the file doc/README.scrapyard for a list of no longer supported boards.

Sandbox Environment:

U-Boot can be built natively to run on a Linux host using the ‘sandbox’ board. This allows feature development which is not board- or architecture- specific to be undertaken on a native platform. The sandbox is also used to run some of U-Boot’s tests.

See doc/arch/sandbox.rst for more details.

Board Initialisation Flow:

This is the intended start-up flow for boards. This should apply for both SPL and U-Boot proper (i.e. they both follow the same rules).

Note: “SPL” stands for “Secondary Program Loader,” which is explained in more detail later in this file.

At present, SPL mostly uses a separate code path, but the function names and roles of each function are the same. Some boards or architectures may not conform to this. At least most ARM boards which use CONFIG_SPL_FRAMEWORK conform to this.

Execution typically starts with an architecture-specific (and possibly CPU-specific) start.S file, such as:

- arch/arm/cpu/armv7/start.S
- arch/powerpc/cpu/mpc83xx/start.S
- arch/mips/cpu/start.S

and so on. From there, three functions are called; the purpose and limitations of each of these functions are described below.

lowlevel_init(): - purpose: essential init to permit execution to reach board_init_f() - no global_data or BSS - there is no stack (ARMv7 may have one but it will soon be removed) - must not set up SDRAM or use console - must only do the bare minimum to allow execution to continue to board_init_f() - this is almost never needed - return normally from this function

board_init_f(): - purpose: set up the machine ready for running board_init_r(): i.e. SDRAM and serial UART - global_data is available - stack is in SRAM - BSS is not available, so you cannot use global/static variables, only stack variables and global_data

Non-SPL-specific notes:
- dram_init() is called to set up DRAM. If already done in SPL this
    can do nothing

SPL-specific notes:
- you can override the entire board_init_f() function with your own
    version as needed.
- preloader_console_init() can be called here in extremis
- should set up SDRAM, and anything needed to make the UART work
- there is no need to clear BSS, it will be done by crt0.S
- for specific scenarios on certain architectures an early BSS *can*
  be made available (via CONFIG_SPL_EARLY_BSS by moving the clearing
  of BSS prior to entering board_init_f()) but doing so is discouraged.
  Instead it is strongly recommended to architect any code changes
  or additions such to not depend on the availability of BSS during
  board_init_f() as indicated in other sections of this README to
  maintain compatibility and consistency across the entire code base.
- must return normally from this function (don't call board_init_r()
    directly)

Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then at this point the stack and global_data are relocated to below CONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top of memory.

board_init_r(): - purpose: main execution, common code - global_data is available - SDRAM is available - BSS is available, all static/global variables can be used - execution eventually continues to main_loop()

Non-SPL-specific notes:
- U-Boot is relocated to the top of memory and is now running from
    there.

SPL-specific notes:
- stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
    CONFIG_SYS_FSL_HAS_CCI400

    Defined For SoC that has cache coherent interconnect
    CCN-400

    CONFIG_SYS_FSL_HAS_CCN504

    Defined for SoC that has cache coherent interconnect CCN-504

The following options need to be configured:

• CPU Type: Define exactly one, e.g. CONFIG_MPC85XX.

• Board Type: Define exactly one, e.g. CONFIG_MPC8540ADS.

• 85xx CPU Options:

    CONFIG_SYS_PPC64
  
    Specifies that the core is a 64-bit PowerPC implementation (implements
    the "64" category of the Power ISA). This is necessary for ePAPR
    compliance, among other possible reasons.
  
    CONFIG_SYS_FSL_ERRATUM_A004510
  
    Enables a workaround for erratum A004510.  If set,
    then CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV and
    CONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLY must be set.
  
    CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV
    CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV2 (optional)
  
    Defines one or two SoC revisions (low 8 bits of SVR)
    for which the A004510 workaround should be applied.
  
    The rest of SVR is either not relevant to the decision
    of whether the erratum is present (e.g. p2040 versus
    p2041) or is implied by the build target, which controls
    whether CONFIG_SYS_FSL_ERRATUM_A004510 is set.
  
    See Freescale App Note 4493 for more information about
    this erratum.
  
    CONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLY
  
    This is the value to write into CCSR offset 0x18600
    according to the A004510 workaround.
  
    CONFIG_SYS_FSL_SINGLE_SOURCE_CLK
    Single Source Clock is clocking mode present in some of FSL SoC's.
    In this mode, a single differential clock is used to supply
    clocks to the sysclock, ddrclock and usbclock.

• Generic CPU options:

    CONFIG_SYS_FSL_DDR
    Freescale DDR driver in use. This type of DDR controller is
    found in mpc83xx, mpc85xx as well as some ARM core SoCs.
  
    CONFIG_SYS_FSL_DDR_ADDR
    Freescale DDR memory-mapped register base.
  
    CONFIG_SYS_FSL_IFC_CLK_DIV
    Defines divider of platform clock(clock input to IFC controller).
  
    CONFIG_SYS_FSL_LBC_CLK_DIV
    Defines divider of platform clock(clock input to eLBC controller).
  
    CONFIG_SYS_FSL_DDR_SDRAM_BASE_PHY
    Physical address from the view of DDR controllers. It is the
    same as CONFIG_SYS_DDR_SDRAM_BASE for  all Power SoCs. But
    it could be different for ARM SoCs.

• MIPS CPU options:

    CONFIG_XWAY_SWAP_BYTES
  
    Enable compilation of tools/xway-swap-bytes needed for Lantiq
    XWAY SoCs for booting from NOR flash. The U-Boot image needs to
    be swapped if a flash programmer is used.

• ARM options:

    CONFIG_SYS_EXCEPTION_VECTORS_HIGH
  
    Select high exception vectors of the ARM core, e.g., do not
    clear the V bit of the c1 register of CP15.
  
    COUNTER_FREQUENCY
    Generic timer clock source frequency.
  
    COUNTER_FREQUENCY_REAL
    Generic timer clock source frequency if the real clock is
    different from COUNTER_FREQUENCY, and can only be determined
    at run time.

• Tegra SoC options:

    CONFIG_TEGRA_SUPPORT_NON_SECURE
  
    Support executing U-Boot in non-secure (NS) mode. Certain
    impossible actions will be skipped if the CPU is in NS mode,
    such as ARM architectural timer initialization.

• Linux Kernel Interface:

    CONFIG_MEMSIZE_IN_BYTES        [relevant for MIPS only]
  
    When transferring memsize parameter to Linux, some versions
    expect it to be in bytes, others in MB.
    Define CONFIG_MEMSIZE_IN_BYTES to make it in bytes.
  
    CONFIG_OF_LIBFDT
  
    New kernel versions are expecting firmware settings to be
    passed using flattened device trees (based on open firmware
    concepts).
  
    CONFIG_OF_LIBFDT
     * New libfdt-based support
     * Adds the "fdt" command
     * The bootm command automatically updates the fdt
  
    OF_TBCLK - The timebase frequency.
  
    boards with QUICC Engines require OF_QE to set UCC MAC
    addresses
  
    CONFIG_OF_IDE_FIXUP
  
    U-Boot can detect if an IDE device is present or not.
    If not, and this new config option is activated, U-Boot
    removes the ATA node from the DTS before booting Linux,
    so the Linux IDE driver does not probe the device and
    crash. This is needed for buggy hardware (uc101) where
    no pull down resistor is connected to the signal IDE5V_DD7.

• vxWorks boot parameters:

    bootvx constructs a valid bootline using the following
    environments variables: bootdev, bootfile, ipaddr, netmask,
    serverip, gatewayip, hostname, othbootargs.
    It loads the vxWorks image pointed bootfile.
  
    Note: If a "bootargs" environment is defined, it will override
    the defaults discussed just above.

• Cache Configuration for ARM:

    CONFIG_SYS_L2_PL310 - Enable support for ARM PL310 L2 cache
                  controller
    CONFIG_SYS_PL310_BASE - Physical base address of PL310
                controller register space

• Serial Ports:

    CONFIG_PL011_CLOCK
  
    If you have Amba PrimeCell PL011 UARTs, set this variable to
    the clock speed of the UARTs.
  
    CONFIG_PL01x_PORTS
  
    If you have Amba PrimeCell PL010 or PL011 UARTs on your board,
    define this to a list of base addresses for each (supported)
    port. See e.g. include/configs/versatile.h
  
    CONFIG_SERIAL_HW_FLOW_CONTROL
  
    Define this variable to enable hw flow control in serial driver.
    Current user of this option is drivers/serial/nsl16550.c driver

• Serial Download Echo Mode:

    CONFIG_LOADS_ECHO
    If defined to 1, all characters received during a
    serial download (using the "loads" command) are
    echoed back. This might be needed by some terminal
    emulations (like "cu"), but may as well just take
    time on others. This setting #define's the initial
    value of the "loads_echo" environment variable.

• Removal of commands

    If no commands are needed to boot, you can disable
    CONFIG_CMDLINE to remove them. In this case, the command line
    will not be available, and when U-Boot wants to execute the
    boot command (on start-up) it will call board_run_command()
    instead. This can reduce image size significantly for very
    simple boot procedures.

• Regular expression support:

    CONFIG_REGEX
    If this variable is defined, U-Boot is linked against
    the SLRE (Super Light Regular Expression) library,
    which adds regex support to some commands, as for
    example "env grep" and "setexpr".

• Watchdog:

    CONFIG_SYS_WATCHDOG_FREQ
    Some platforms automatically call WATCHDOG_RESET()
    from the timer interrupt handler every
    CONFIG_SYS_WATCHDOG_FREQ interrupts. If not set by the
    board configuration file, a default of CONFIG_SYS_HZ/2
    (i.e. 500) is used. Setting CONFIG_SYS_WATCHDOG_FREQ
    to 0 disables calling WATCHDOG_RESET() from the timer
    interrupt.

• Real-Time Clock:

    When CONFIG_CMD_DATE is selected, the type of the RTC
    has to be selected, too. Define exactly one of the
    following options:
  
    CONFIG_RTC_PCF8563    - use Philips PCF8563 RTC
    CONFIG_RTC_MC13XXX    - use MC13783 or MC13892 RTC
    CONFIG_RTC_MC146818    - use MC146818 RTC
    CONFIG_RTC_DS1307    - use Maxim, Inc. DS1307 RTC
    CONFIG_RTC_DS1337    - use Maxim, Inc. DS1337 RTC
    CONFIG_RTC_DS1338    - use Maxim, Inc. DS1338 RTC
    CONFIG_RTC_DS1339    - use Maxim, Inc. DS1339 RTC
    CONFIG_RTC_DS164x    - use Dallas DS164x RTC
    CONFIG_RTC_ISL1208    - use Intersil ISL1208 RTC
    CONFIG_RTC_MAX6900    - use Maxim, Inc. MAX6900 RTC
    CONFIG_RTC_DS1337_NOOSC    - Turn off the OSC output for DS1337
    CONFIG_SYS_RV3029_TCR    - enable trickle charger on
                  RV3029 RTC.
  
    Note that if the RTC uses I2C, then the I2C interface
    must also be configured. See I2C Support, below.

• GPIO Support:

    CONFIG_PCA953X        - use NXP's PCA953X series I2C GPIO
  
    The CONFIG_SYS_I2C_PCA953X_WIDTH option specifies a list of
    chip-ngpio pairs that tell the PCA953X driver the number of
    pins supported by a particular chip.
  
    Note that if the GPIO device uses I2C, then the I2C interface
    must also be configured. See I2C Support, below.

• I/O tracing:

    When CONFIG_IO_TRACE is selected, U-Boot intercepts all I/O
    accesses and can checksum them or write a list of them out
    to memory. See the 'iotrace' command for details. This is
    useful for testing device drivers since it can confirm that
    the driver behaves the same way before and after a code
    change. Currently this is supported on sandbox and arm. To
    add support for your architecture, add '#include <iotrace.h>'
    to the bottom of arch/<arch>/include/asm/io.h and test.
  
    Example output from the 'iotrace stats' command is below.
    Note that if the trace buffer is exhausted, the checksum will
    still continue to operate.
  
        iotrace is enabled
        Start:  10000000    (buffer start address)
        Size:   00010000    (buffer size)
        Offset: 00000120    (current buffer offset)
        Output: 10000120    (start + offset)
        Count:  00000018    (number of trace records)
        CRC32:  9526fb66    (CRC32 of all trace records)

• Timestamp Support:

    When CONFIG_TIMESTAMP is selected, the timestamp
    (date and time) of an image is printed by image
    commands like bootm or iminfo. This option is
    automatically enabled when you select CONFIG_CMD_DATE .

• Partition Labels (disklabels) Supported:

    Zero or more of the following:
    CONFIG_MAC_PARTITION   Apple's MacOS partition table.
    CONFIG_ISO_PARTITION   ISO partition table, used on CDROM etc.
    CONFIG_EFI_PARTITION   GPT partition table, common when EFI is the
                   bootloader.  Note 2TB partition limit; see
                   disk/part_efi.c
    CONFIG_SCSI) you must configure support for at
    least one non-MTD partition type as well.

• NETWORK Support (PCI):

    CONFIG_E1000_SPI
    Utility code for direct access to the SPI bus on Intel 8257x.
    This does not do anything useful unless you set at least one
    of CONFIG_CMD_E1000 or CONFIG_E1000_SPI_GENERIC.
  
    CONFIG_NATSEMI
    Support for National dp83815 chips.
  
    CONFIG_NS8382X
    Support for National dp8382[01] gigabit chips.

• NETWORK Support (other):

    CONFIG_CALXEDA_XGMAC
    Support for the Calxeda XGMAC device
  
    CONFIG_LAN91C96
    Support for SMSC's LAN91C96 chips.
  
        CONFIG_LAN91C96_USE_32_BIT
        Define this to enable 32 bit addressing
  
        CONFIG_SYS_DAVINCI_EMAC_PHY_COUNT
        Define this if you have more then 3 PHYs.
  
    CONFIG_FTGMAC100
    Support for Faraday's FTGMAC100 Gigabit SoC Ethernet
  
        CONFIG_FTGMAC100_EGIGA
        Define this to use GE link update with gigabit PHY.
        Define this if FTGMAC100 is connected to gigabit PHY.
        If your system has 10/100 PHY only, it might not occur
        wrong behavior. Because PHY usually return timeout or
        useless data when polling gigabit status and gigabit
        control registers. This behavior won't affect the
        correctnessof 10/100 link speed update.
  
    CONFIG_SH_ETHER
    Support for Renesas on-chip Ethernet controller
  
        CONFIG_SH_ETHER_USE_PORT
        Define the number of ports to be used
  
        CONFIG_SH_ETHER_PHY_ADDR
        Define the ETH PHY's address
  
        CONFIG_SH_ETHER_CACHE_WRITEBACK
        If this option is set, the driver enables cache flush.

• TPM Support:

    CONFIG_TPM
    Support TPM devices.
  
    CONFIG_TPM_TIS_INFINEON
    Support for Infineon i2c bus TPM devices. Only one device
    per system is supported at this time.
  
        CONFIG_TPM_TIS_I2C_BURST_LIMITATION
        Define the burst count bytes upper limit
  
    CONFIG_TPM_ST33ZP24
    Support for STMicroelectronics TPM devices. Requires DM_TPM support.
  
        CONFIG_TPM_ST33ZP24_I2C
        Support for STMicroelectronics ST33ZP24 I2C devices.
        Requires TPM_ST33ZP24 and I2C.
  
        CONFIG_TPM_ST33ZP24_SPI
        Support for STMicroelectronics ST33ZP24 SPI devices.
        Requires TPM_ST33ZP24 and SPI.
  
    CONFIG_TPM_ATMEL_TWI
    Support for Atmel TWI TPM device. Requires I2C support.
  
    CONFIG_TPM_TIS_LPC
    Support for generic parallel port TPM devices. Only one device
    per system is supported at this time.
  
        CONFIG_TPM_TIS_BASE_ADDRESS
        Base address where the generic TPM device is mapped
        to. Contemporary x86 systems usually map it at
        0xfed40000.
  
    CONFIG_TPM
    Define this to enable the TPM support library which provides
    functional interfaces to some TPM commands.
    Requires support for a TPM device.
  
    CONFIG_TPM_AUTH_SESSIONS
    Define this to enable authorized functions in the TPM library.
    Requires CONFIG_TPM and CONFIG_SHA1.

• USB Support:

    At the moment only the UHCI host controller is
    supported (PIP405, MIP405); define
    CONFIG_USB_UHCI to enable it.
    define CONFIG_USB_KEYBOARD to enable the USB Keyboard
    and define CONFIG_USB_STORAGE to enable the USB
    storage devices.
    Note:
    Supported are USB Keyboards and USB Floppy drives
    (TEAC FD-05PUB).
  
    CONFIG_USB_DWC2_REG_ADDR the physical CPU address of the DWC2
    HW module registers.

• USB Device:

    Define the below if you wish to use the USB console.
    Once firmware is rebuilt from a serial console issue the
    command "setenv stdin usbtty; setenv stdout usbtty" and
    attach your USB cable. The Unix command "dmesg" should print
    it has found a new device. The environment variable usbtty
    can be set to gserial or cdc_acm to enable your device to
    appear to a USB host as a Linux gserial device or a
    Common Device Class Abstract Control Model serial device.
    If you select usbtty = gserial you should be able to enumerate
    a Linux host by
    # modprobe usbserial vendor=0xVendorID product=0xProductID
    else if using cdc_acm, simply setting the environment
    variable usbtty to be cdc_acm should suffice. The following
    might be defined in YourBoardName.h
  
        CONFIG_USB_DEVICE
        Define this to build a UDC device
  
        CONFIG_USB_TTY
        Define this to have a tty type of device available to
        talk to the UDC device
  
        CONFIG_USBD_HS
        Define this to enable the high speed support for usb
        device and usbtty. If this feature is enabled, a routine
        int is_usbd_high_speed(void)
        also needs to be defined by the driver to dynamically poll
        whether the enumeration has succeded at high speed or full
        speed.
  
    If you have a USB-IF assigned VendorID then you may wish to
    define your own vendor specific values either in BoardName.h
    or directly in usbd_vendor_info.h. If you don't define
    CONFIG_USBD_MANUFACTURER, CONFIG_USBD_PRODUCT_NAME,
    CONFIG_USBD_VENDORID and CONFIG_USBD_PRODUCTID, then U-Boot
    should pretend to be a Linux device to it's target host.
  
        CONFIG_USBD_MANUFACTURER
        Define this string as the name of your company for
        - CONFIG_USBD_MANUFACTURER "my company"
  
        CONFIG_USBD_PRODUCT_NAME
        Define this string as the name of your product
        - CONFIG_USBD_PRODUCT_NAME "acme usb device"
  
        CONFIG_USBD_VENDORID
        Define this as your assigned Vendor ID from the USB
        Implementors Forum. This *must* be a genuine Vendor ID
        to avoid polluting the USB namespace.
        - CONFIG_USBD_VENDORID 0xFFFF
  
        CONFIG_USBD_PRODUCTID
        Define this as the unique Product ID
        for your device
        - CONFIG_USBD_PRODUCTID 0xFFFF

• ULPI Layer Support:

    The ULPI (UTMI Low Pin (count) Interface) PHYs are supported via
    the generic ULPI layer. The generic layer accesses the ULPI PHY
    via the platform viewport, so you need both the genric layer and
    the viewport enabled. Currently only Chipidea/ARC based
    viewport is supported.
    To enable the ULPI layer support, define CONFIG_USB_ULPI and
    CONFIG_USB_ULPI_VIEWPORT in your board configuration file.
    If your ULPI phy needs a different reference clock than the
    standard 24 MHz then you have to define CONFIG_ULPI_REF_CLK to
    the appropriate value in Hz.

• MMC Support:

    CONFIG_SH_MMCIF
    Support for Renesas on-chip MMCIF controller
  
        CONFIG_SH_MMCIF_ADDR
        Define the base address of MMCIF registers
  
        CONFIG_SH_MMCIF_CLK
        Define the clock frequency for MMCIF

• USB Device Firmware Update (DFU) class support:

    CONFIG_DFU_OVER_USB
    This enables the USB portion of the DFU USB class
  
    CONFIG_DFU_NAND
    This enables support for exposing NAND devices via DFU.
  
    CONFIG_DFU_RAM
    This enables support for exposing RAM via DFU.
    Note: DFU spec refer to non-volatile memory usage, but
    allow usages beyond the scope of spec - here RAM usage,
    one that would help mostly the developer.
  
    CONFIG_SYS_DFU_DATA_BUF_SIZE
    Dfu transfer uses a buffer before writing data to the
    raw storage device. Make the size (in bytes) of this buffer
    configurable. The size of this buffer is also configurable
    through the "dfu_bufsiz" environment variable.
  
    CONFIG_SYS_DFU_MAX_FILE_SIZE
    When updating files rather than the raw storage device,
    we use a static buffer to copy the file into and then write
    the buffer once we've been given the whole file.  Define
    this to the maximum filesize (in bytes) for the buffer.
    Default is 4 MiB if undefined.
  
    DFU_DEFAULT_POLL_TIMEOUT
    Poll timeout [ms], is the timeout a device can send to the
    host. The host must wait for this timeout before sending
    a subsequent DFU_GET_STATUS request to the device.
  
    DFU_MANIFEST_POLL_TIMEOUT
    Poll timeout [ms], which the device sends to the host when
    entering dfuMANIFEST state. Host waits this timeout, before
    sending again an USB request to the device.

• Journaling Flash filesystem support:

    CONFIG_SYS_JFFS2_FIRST_SECTOR,
    CONFIG_SYS_JFFS2_FIRST_BANK, CONFIG_SYS_JFFS2_NUM_BANKS
    Define these for a default partition on a NOR device

• Keyboard Support:

    See Kconfig help for available keyboard drivers.

• LCD Support: CONFIG_LCD

    Define this to enable LCD support (for output to LCD
    display); also select one of the supported displays
    by defining one of these:
  
    CONFIG_NEC_NL6448AC33:
  
        NEC NL6448AC33-18. Active, color, single scan.
  
    CONFIG_NEC_NL6448BC20
  
        NEC NL6448BC20-08. 6.5", 640x480.
        Active, color, single scan.
  
    CONFIG_NEC_NL6448BC33_54
  
        NEC NL6448BC33-54. 10.4", 640x480.
        Active, color, single scan.
  
    CONFIG_SHARP_16x9
  
        Sharp 320x240. Active, color, single scan.
        It isn't 16x9, and I am not sure what it is.
  
    CONFIG_SHARP_LQ64D341
  
        Sharp LQ64D341 display, 640x480.
        Active, color, single scan.
  
    CONFIG_HLD1045
  
        HLD1045 display, 640x480.
        Active, color, single scan.
  
    CONFIG_OPTREX_BW
  
        Optrex     CBL50840-2 NF-FW 99 22 M5
        or
        Hitachi     LMG6912RPFC-00T
        or
        Hitachi     SP14Q002
  
        320x240. Black & white.
  
    CONFIG_LCD_ALIGNMENT
  
    Normally the LCD is page-aligned (typically 4KB). If this is
    defined then the LCD will be aligned to this value instead.
    For ARM it is sometimes useful to use MMU_SECTION_SIZE
    here, since it is cheaper to change data cache settings on
    a per-section basis.

    CONFIG_LCD_ROTATION

    Sometimes, for example if the display is mounted in portrait
    mode or even if it's mounted landscape but rotated by 180degree,
    we need to rotate our content of the display relative to the
    framebuffer, so that user can read the messages which are
    printed out.
    Once CONFIG_LCD_ROTATION is defined, the lcd_console will be
    initialized with a given rotation from "vl_rot" out of
    "vidinfo_t" which is provided by the board specific code.
    The value for vl_rot is coded as following (matching to
    fbcon=rotate:<n> linux-kernel commandline):
    0 = no rotation respectively 0 degree
    1 = 90 degree rotation
    2 = 180 degree rotation
    3 = 270 degree rotation

    If CONFIG_LCD_ROTATION is not defined, the console will be
    initialized with 0degree rotation.

• MII/PHY support:

    CONFIG_PHY_CLOCK_FREQ (ppc4xx)
  
    The clock frequency of the MII bus
  
    CONFIG_PHY_CMD_DELAY (ppc4xx)
  
    Some PHY like Intel LXT971A need extra delay after
    command issued before MII status register can be read

• IP address:

    CONFIG_IPADDR
  
    Define a default value for the IP address to use for
    the default Ethernet interface, in case this is not
    determined through e.g. bootp.
    (Environment variable "ipaddr")

• Server IP address:

    CONFIG_SERVERIP
  
    Defines a default value for the IP address of a TFTP
    server to contact when using the "tftboot" command.
    (Environment variable "serverip")

• Gateway IP address:

    CONFIG_GATEWAYIP
  
    Defines a default value for the IP address of the
    default router where packets to other networks are
    sent to.
    (Environment variable "gatewayip")

• Subnet mask:

    CONFIG_NETMASK
  
    Defines a default value for the subnet mask (or
    routing prefix) which is used to determine if an IP
    address belongs to the local subnet or needs to be
    forwarded through a router.
    (Environment variable "netmask")

• BOOTP Recovery Mode:

    CONFIG_BOOTP_RANDOM_DELAY
  
    If you have many targets in a network that try to
    boot using BOOTP, you may want to avoid that all
    systems send out BOOTP requests at precisely the same
    moment (which would happen for instance at recovery
    from a power failure, when all systems will try to
    boot, thus flooding the BOOTP server. Defining
    CONFIG_BOOTP_RANDOM_DELAY causes a random delay to be
    inserted before sending out BOOTP requests. The
    following delays are inserted then:
  
    1st BOOTP request:    delay 0 ... 1 sec
    2nd BOOTP request:    delay 0 ... 2 sec
    3rd BOOTP request:    delay 0 ... 4 sec
    4th and following
    BOOTP requests:        delay 0 ... 8 sec
  
    CONFIG_BOOTP_ID_CACHE_SIZE
  
    BOOTP packets are uniquely identified using a 32-bit ID. The
    server will copy the ID from client requests to responses and
    U-Boot will use this to determine if it is the destination of
    an incoming response. Some servers will check that addresses
    aren't in use before handing them out (usually using an ARP
    ping) and therefore take up to a few hundred milliseconds to
    respond. Network congestion may also influence the time it
    takes for a response to make it back to the client. If that
    time is too long, U-Boot will retransmit requests. In order
    to allow earlier responses to still be accepted after these
    retransmissions, U-Boot's BOOTP client keeps a small cache of
    IDs. The CONFIG_BOOTP_ID_CACHE_SIZE controls the size of this
    cache. The default is to keep IDs for up to four outstanding
    requests. Increasing this will allow U-Boot to accept offers
    from a BOOTP client in networks with unusually high latency.

• DHCP Advanced Options:

• Link-local IP address negotiation:

   Negotiate with other link-local clients on the local network
   for an address that doesn't require explicit configuration.
   This is especially useful if a DHCP server cannot be guaranteed
   to exist in all environments that the device must operate.
  
   See doc/README.link-local for more information.

• MAC address from environment variables

   FDT_SEQ_MACADDR_FROM_ENV
  
   Fix-up device tree with MAC addresses fetched sequentially from
   environment variables. This config work on assumption that
   non-usable ethernet node of device-tree are either not present
   or their status has been marked as "disabled".

• CDP Options:

   CONFIG_CDP_DEVICE_ID
  
   The device id used in CDP trigger frames.
  
   CONFIG_CDP_DEVICE_ID_PREFIX
  
   A two character string which is prefixed to the MAC address
   of the device.
  
   CONFIG_CDP_PORT_ID
  
   A printf format string which contains the ascii name of
   the port. Normally is set to "eth%d" which sets
   eth0 for the first Ethernet, eth1 for the second etc.
  
   CONFIG_CDP_CAPABILITIES
  
   A 32bit integer which indicates the device capabilities;
   0x00000010 for a normal host which does not forwards.
  
   CONFIG_CDP_VERSION
  
   An ascii string containing the version of the software.
  
   CONFIG_CDP_PLATFORM
  
   An ascii string containing the name of the platform.
  
   CONFIG_CDP_TRIGGER
  
   A 32bit integer sent on the trigger.
  
   CONFIG_CDP_POWER_CONSUMPTION
  
   A 16bit integer containing the power consumption of the
   device in .1 of milliwatts.
  
   CONFIG_CDP_APPLIANCE_VLAN_TYPE
  
   A byte containing the id of the VLAN.

• Status LED: CONFIG_LED_STATUS

    Several configurations allow to display the current
    status using a LED. For instance, the LED will blink
    fast while running U-Boot code, stop blinking as
    soon as a reply to a BOOTP request was received, and
    start blinking slow once the Linux kernel is running
    (supported by a status LED driver in the Linux
    kernel). Defining CONFIG_LED_STATUS enables this
    feature in U-Boot.
  
    Additional options:
  
    CONFIG_LED_STATUS_GPIO
    The status LED can be connected to a GPIO pin.
    In such cases, the gpio_led driver can be used as a
    status LED backend implementation. Define CONFIG_LED_STATUS_GPIO
    to include the gpio_led driver in the U-Boot binary.
  
    CONFIG_GPIO_LED_INVERTED_TABLE
    Some GPIO connected LEDs may have inverted polarity in which
    case the GPIO high value corresponds to LED off state and
    GPIO low value corresponds to LED on state.
    In such cases CONFIG_GPIO_LED_INVERTED_TABLE may be defined
    with a list of GPIO LEDs that have inverted polarity.

• I2C Support:

    CONFIG_SYS_NUM_I2C_BUSES
    Hold the number of i2c buses you want to use.
  
    CONFIG_SYS_I2C_DIRECT_BUS
    define this, if you don't use i2c muxes on your hardware.
    if CONFIG_SYS_I2C_MAX_HOPS is not defined or == 0 you can
    omit this define.
  
    CONFIG_SYS_I2C_MAX_HOPS
    define how many muxes are maximal consecutively connected
    on one i2c bus. If you not use i2c muxes, omit this
    define.
  
    CONFIG_SYS_I2C_BUSES
    hold a list of buses you want to use, only used if
    CONFIG_SYS_I2C_DIRECT_BUS is not defined, for example
    a board with CONFIG_SYS_I2C_MAX_HOPS = 1 and
    CONFIG_SYS_NUM_I2C_BUSES = 9:
  
     CONFIG_SYS_I2C_BUSES    {{0, {I2C_NULL_HOP}}, \
                {0, {{I2C_MUX_PCA9547, 0x70, 1}}}, \
                {0, {{I2C_MUX_PCA9547, 0x70, 2}}}, \
                {0, {{I2C_MUX_PCA9547, 0x70, 3}}}, \
                {0, {{I2C_MUX_PCA9547, 0x70, 4}}}, \
                {0, {{I2C_MUX_PCA9547, 0x70, 5}}}, \
                {1, {I2C_NULL_HOP}}, \
                {1, {{I2C_MUX_PCA9544, 0x72, 1}}}, \
                {1, {{I2C_MUX_PCA9544, 0x72, 2}}}, \
                }
  
    which defines
        bus 0 on adapter 0 without a mux
        bus 1 on adapter 0 with a PCA9547 on address 0x70 port 1
        bus 2 on adapter 0 with a PCA9547 on address 0x70 port 2
        bus 3 on adapter 0 with a PCA9547 on address 0x70 port 3
        bus 4 on adapter 0 with a PCA9547 on address 0x70 port 4
        bus 5 on adapter 0 with a PCA9547 on address 0x70 port 5
        bus 6 on adapter 1 without a mux
        bus 7 on adapter 1 with a PCA9544 on address 0x72 port 1
        bus 8 on adapter 1 with a PCA9544 on address 0x72 port 2
  
    If you do not have i2c muxes on your board, omit this define.

• Legacy I2C Support:

    If you use the software i2c interface (CONFIG_SYS_I2C_SOFT)
    then the following macros need to be defined (examples are
    from include/configs/lwmon.h):
  
    I2C_INIT
  
    (Optional). Any commands necessary to enable the I2C
    controller or configure ports.
  
    eg: #define I2C_INIT (immr->im_cpm.cp_pbdir |=    PB_SCL)
  
    I2C_ACTIVE
  
    The code necessary to make the I2C data line active
    (driven).  If the data line is open collector, this
    define can be null.
  
    eg: #define I2C_ACTIVE (immr->im_cpm.cp_pbdir |=  PB_SDA)
  
    I2C_TRISTATE
  
    The code necessary to make the I2C data line tri-stated
    (inactive).  If the data line is open collector, this
    define can be null.
  
    eg: #define I2C_TRISTATE (immr->im_cpm.cp_pbdir &= ~PB_SDA)
  
    I2C_READ
  
    Code that returns true if the I2C data line is high,
    false if it is low.
  
    eg: #define I2C_READ ((immr->im_cpm.cp_pbdat & PB_SDA) != 0)
  
    I2C_SDA(bit)
  
    If <bit> is true, sets the I2C data line high. If it
    is false, it clears it (low).
  
    eg: #define I2C_SDA(bit) \
        if(bit) immr->im_cpm.cp_pbdat |=  PB_SDA; \
        else    immr->im_cpm.cp_pbdat &= ~PB_SDA
  
    I2C_SCL(bit)
  
    If <bit> is true, sets the I2C clock line high. If it
    is false, it clears it (low).
  
    eg: #define I2C_SCL(bit) \
        if(bit) immr->im_cpm.cp_pbdat |=  PB_SCL; \
        else    immr->im_cpm.cp_pbdat &= ~PB_SCL
  
    I2C_DELAY
  
    This delay is invoked four times per clock cycle so this
    controls the rate of data transfer.  The data rate thus
    is 1 / (I2C_DELAY * 4). Often defined to be something
    like:
  
    #define I2C_DELAY  udelay(2)
  
    CONFIG_SOFT_I2C_GPIO_SCL / CONFIG_SOFT_I2C_GPIO_SDA
  
    If your arch supports the generic GPIO framework (asm/gpio.h),
    then you may alternatively define the two GPIOs that are to be
    used as SCL / SDA.  Any of the previous I2C_xxx macros will
    have GPIO-based defaults assigned to them as appropriate.
  
    You should define these to the GPIO value as given directly to
    the generic GPIO functions.
  
    CONFIG_SYS_I2C_INIT_BOARD
  
    When a board is reset during an i2c bus transfer
    chips might think that the current transfer is still
    in progress. On some boards it is possible to access
    the i2c SCLK line directly, either by using the
    processor pin as a GPIO or by having a second pin
    connected to the bus. If this option is defined a
    custom i2c_init_board() routine in boards/xxx/board.c
    is run early in the boot sequence.
  
    CONFIG_I2C_MULTI_BUS
  
    This option allows the use of multiple I2C buses, each of which
    must have a controller.     At any point in time, only one bus is
    active.     To switch to a different bus, use the 'i2c dev' command.
    Note that bus numbering is zero-based.
  
    CONFIG_SYS_I2C_NOPROBES
  
    This option specifies a list of I2C devices that will be skipped
    when the 'i2c probe' command is issued.     If CONFIG_I2C_MULTI_BUS
    is set, specify a list of bus-device pairs.  Otherwise, specify
    a 1D array of device addresses
  
    e.g.
        #undef    CONFIG_I2C_MULTI_BUS
        #define CONFIG_SYS_I2C_NOPROBES {0x50,0x68}
  
    will skip addresses 0x50 and 0x68 on a board with one I2C bus
  
        #define CONFIG_I2C_MULTI_BUS
        #define CONFIG_SYS_I2C_NOPROBES    {{0,0x50},{0,0x68},{1,0x54}}
  
    will skip addresses 0x50 and 0x68 on bus 0 and address 0x54 on bus 1
  
    CONFIG_SYS_RTC_BUS_NUM
  
    If defined, then this indicates the I2C bus number for the RTC.
    If not defined, then U-Boot assumes that RTC is on I2C bus 0.
  
    CONFIG_SOFT_I2C_READ_REPEATED_START
  
    defining this will force the i2c_read() function in
    the soft_i2c driver to perform an I2C repeated start
    between writing the address pointer and reading the
    data.  If this define is omitted the default behaviour
    of doing a stop-start sequence will be used.  Most I2C
    devices can use either method, but some require one or
    the other.

• SPI Support: CONFIG_SPI

    Enables SPI driver (so far only tested with
    SPI EEPROM, also an instance works with Crystal A/D and
    D/As on the SACSng board)
  
    CONFIG_SYS_SPI_MXC_WAIT
    Timeout for waiting until spi transfer completed.
    default: (CONFIG_SYS_HZ/100)     /* 10 ms */

• FPGA Support: CONFIG_FPGA

    Enables FPGA subsystem.
  
    CONFIG_FPGA_<vendor>
  
    Enables support for specific chip vendors.
    (ALTERA, XILINX)
  
    CONFIG_FPGA_<family>
  
    Enables support for FPGA family.
    (SPARTAN2, SPARTAN3, VIRTEX2, CYCLONE2, ACEX1K, ACEX)
  
    CONFIG_SYS_FPGA_CHECK_BUSY
  
    Enable checks on FPGA configuration interface busy
    status by the configuration function. This option
    will require a board or device specific function to
    be written.
  
    CONFIG_FPGA_DELAY
  
    If defined, a function that provides delays in the FPGA
    configuration driver.
  
    CONFIG_SYS_FPGA_CHECK_ERROR
  
    Check for configuration errors during FPGA bitfile
    loading. For example, abort during Virtex II
    configuration if the INIT_B line goes low (which
    indicated a CRC error).
  
    CONFIG_SYS_FPGA_WAIT_INIT
  
    Maximum time to wait for the INIT_B line to de-assert
    after PROB_B has been de-asserted during a Virtex II
    FPGA configuration sequence. The default time is 500
    ms.
  
    CONFIG_SYS_FPGA_WAIT_BUSY
  
    Maximum time to wait for BUSY to de-assert during
    Virtex II FPGA configuration. The default is 5 ms.
  
    CONFIG_SYS_FPGA_WAIT_CONFIG
  
    Time to wait after FPGA configuration. The default is
    200 ms.

• Vendor Parameter Protection:

    U-Boot considers the values of the environment
    variables "serial#" (Board Serial Number) and
    "ethaddr" (Ethernet Address) to be parameters that
    are set once by the board vendor / manufacturer, and
    protects these variables from casual modification by
    the user. Once set, these variables are read-only,
    and write or delete attempts are rejected. You can
    change this behaviour:
  
    If CONFIG_ENV_OVERWRITE is #defined in your config
    file, the write protection for vendor parameters is
    completely disabled. Anybody can change or delete
    these parameters.
  
    Alternatively, if you define _both_ an ethaddr in the
    default env _and_ CONFIG_OVERWRITE_ETHADDR_ONCE, a default
    Ethernet address is installed in the environment,
    which can be changed exactly ONCE by the user. [The
    serial# is unaffected by this, i. e. it remains
    read-only.]
  
    The same can be accomplished in a more flexible way
    for any variable by configuring the type of access
    to allow for those variables in the ".flags" variable
    or define CONFIG_ENV_FLAGS_LIST_STATIC.

• Protected RAM:

    CONFIG_PRAM
  
    Define this variable to enable the reservation of
    "protected RAM", i. e. RAM which is not overwritten
    by U-Boot. Define CONFIG_PRAM to hold the number of
    kB you want to reserve for pRAM. You can overwrite
    this default value by defining an environment
    variable "pram" to the number of kB you want to
    reserve. Note that the board info structure will
    still show the full amount of RAM. If pRAM is
    reserved, a new environment variable "mem" will
    automatically be defined to hold the amount of
    remaining RAM in a form that can be passed as boot
    argument to Linux, for instance like that:
  
        setenv bootargs ... mem=\${mem}
        saveenv
  
    This way you can tell Linux not to use this memory,
    either, which results in a memory region that will
    not be affected by reboots.
  
    *WARNING* If your board configuration uses automatic
    detection of the RAM size, you must make sure that
    this memory test is non-destructive. So far, the
    following board configurations are known to be
    "pRAM-clean":
  
        IVMS8, IVML24, SPD8xx,
        HERMES, IP860, RPXlite, LWMON,
        FLAGADM

• Error Recovery: Note:

    In the current implementation, the local variables
    space and global environment variables space are
    separated. Local variables are those you define by
    simply typing `name=value'. To access a local
    variable later on, you have write `$name' or
    `${name}'; to execute the contents of a variable
    directly type `$name' at the command prompt.
  
    Global environment variables are those you use
    setenv/printenv to work with. To run a command stored
    in such a variable, you need to use the run command,
    and you must not use the '
  #39; sign to access them.
  
    To store commands and special characters in a
    variable, please use double quotation marks
    surrounding the whole text of the variable, instead
    of the backslashes before semicolons and special
    symbols.

• Default Environment:

    CONFIG_EXTRA_ENV_SETTINGS
  
    Define this to contain any number of null terminated
    strings (variable = value pairs) that will be part of
    the default environment compiled into the boot image.
  
    For example, place something like this in your
    board's config file:
  
    #define CONFIG_EXTRA_ENV_SETTINGS \
        "myvar1=value1\0" \
        "myvar2=value2\0"
  
    Warning: This method is based on knowledge about the
    internal format how the environment is stored by the
    U-Boot code. This is NOT an official, exported
    interface! Although it is unlikely that this format
    will change soon, there is no guarantee either.
    You better know what you are doing here.
  
    Note: overly (ab)use of the default environment is
    discouraged. Make sure to check other ways to preset
    the environment like the "source" command or the
    boot command first.
  
    CONFIG_DELAY_ENVIRONMENT
  
    Normally the environment is loaded when the board is
    initialised so that it is available to U-Boot. This inhibits
    that so that the environment is not available until
    explicitly loaded later by U-Boot code. With CONFIG_OF_CONTROL
    this is instead controlled by the value of
    /config/load-environment.
  
    CONFIG_STANDALONE_LOAD_ADDR
  
    This option defines a board specific value for the
    address where standalone program gets loaded, thus
    overwriting the architecture dependent default
    settings.

• Automatic software updates via TFTP server

    CONFIG_UPDATE_TFTP
    CONFIG_UPDATE_TFTP_CNT_MAX
    CONFIG_UPDATE_TFTP_MSEC_MAX
  
    These options enable and control the auto-update feature;
    for a more detailed description refer to doc/README.update.

• MTD Support (mtdparts command, UBI support)

    CONFIG_MTD_UBI_WL_THRESHOLD
    This parameter defines the maximum difference between the highest
    erase counter value and the lowest erase counter value of eraseblocks
    of UBI devices. When this threshold is exceeded, UBI starts performing
    wear leveling by means of moving data from eraseblock with low erase
    counter to eraseblocks with high erase counter.
  
    The default value should be OK for SLC NAND flashes, NOR flashes and
    other flashes which have eraseblock life-cycle 100000 or more.
    However, in case of MLC NAND flashes which typically have eraseblock
    life-cycle less than 10000, the threshold should be lessened (e.g.,
    to 128 or 256, although it does not have to be power of 2).
  
    default: 4096
  
    CONFIG_MTD_UBI_BEB_LIMIT
    This option specifies the maximum bad physical eraseblocks UBI
    expects on the MTD device (per 1024 eraseblocks). If the
    underlying flash does not admit of bad eraseblocks (e.g. NOR
    flash), this value is ignored.
  
    NAND datasheets often specify the minimum and maximum NVM
    (Number of Valid Blocks) for the flashes' endurance lifetime.
    The maximum expected bad eraseblocks per 1024 eraseblocks
    then can be calculated as "1024 * (1 - MinNVB / MaxNVB)",
    which gives 20 for most NANDs (MaxNVB is basically the total
    count of eraseblocks on the chip).
  
    To put it differently, if this value is 20, UBI will try to
    reserve about 1.9% of physical eraseblocks for bad blocks
    handling. And that will be 1.9% of eraseblocks on the entire
    NAND chip, not just the MTD partition UBI attaches. This means
    that if you have, say, a NAND flash chip admits maximum 40 bad
    eraseblocks, and it is split on two MTD partitions of the same
    size, UBI will reserve 40 eraseblocks when attaching a
    partition.
  
    default: 20
  
    CONFIG_MTD_UBI_FASTMAP
    Fastmap is a mechanism which allows attaching an UBI device
    in nearly constant time. Instead of scanning the whole MTD device it
    only has to locate a checkpoint (called fastmap) on the device.
    The on-flash fastmap contains all information needed to attach
    the device. Using fastmap makes only sense on large devices where
    attaching by scanning takes long. UBI will not automatically install
    a fastmap on old images, but you can set the UBI parameter
    CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT to 1 if you want so. Please note
    that fastmap-enabled images are still usable with UBI implementations
    without    fastmap support. On typical flash devices the whole fastmap
    fits into one PEB. UBI will reserve PEBs to hold two fastmaps.
  
    CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT
    Set this parameter to enable fastmap automatically on images
    without a fastmap.
    default: 0
  
    CONFIG_MTD_UBI_FM_DEBUG
    Enable UBI fastmap debug
    default: 0

• SPL framework

    CONFIG_SPL
    Enable building of SPL globally.
  
    CONFIG_SPL_PANIC_ON_RAW_IMAGE
    When defined, SPL will panic() if the image it has
    loaded does not have a signature.
    Defining this is useful when code which loads images
    in SPL cannot guarantee that absolutely all read errors
    will be caught.
    An example is the LPC32XX MLC NAND driver, which will
    consider that a completely unreadable NAND block is bad,
    and thus should be skipped silently.
  
    CONFIG_SPL_DISPLAY_PRINT
    For ARM, enable an optional function to print more information
    about the running system.
  
    CONFIG_SPL_MPC83XX_WAIT_FOR_NAND
    Set this for NAND SPL on PPC mpc83xx targets, so that
    start.S waits for the rest of the SPL to load before
    continuing (the hardware starts execution after just
    loading the first page rather than the full 4K).
  
    CONFIG_SPL_UBI
    Support for a lightweight UBI (fastmap) scanner and
    loader
  
    CONFIG_SYS_NAND_5_ADDR_CYCLE, CONFIG_SYS_NAND_PAGE_COUNT,
    CONFIG_SYS_NAND_PAGE_SIZE, CONFIG_SYS_NAND_OOBSIZE,
    CONFIG_SYS_NAND_BLOCK_SIZE, CONFIG_SYS_NAND_BAD_BLOCK_POS,
    CONFIG_SYS_NAND_ECCPOS, CONFIG_SYS_NAND_ECCSIZE,
    CONFIG_SYS_NAND_ECCBYTES
    Defines the size and behavior of the NAND that SPL uses
    to read U-Boot
  
    CONFIG_SYS_NAND_U_BOOT_DST
    Location in memory to load U-Boot to
  
    CONFIG_SYS_NAND_U_BOOT_SIZE
    Size of image to load
  
    CONFIG_SYS_NAND_U_BOOT_START
    Entry point in loaded image to jump to
  
    CONFIG_SYS_NAND_HW_ECC_OOBFIRST
    Define this if you need to first read the OOB and then the
    data. This is used, for example, on davinci platforms.
  
    CONFIG_SPL_RAM_DEVICE
    Support for running image already present in ram, in SPL binary
  
    CONFIG_SPL_FIT_PRINT
    Printing information about a FIT image adds quite a bit of
    code to SPL. So this is normally disabled in SPL. Use this
    option to re-enable it. This will affect the output of the
    bootm command when booting a FIT image.

• Interrupt support (PPC):

    There are common interrupt_init() and timer_interrupt()
    for all PPC archs. interrupt_init() calls interrupt_init_cpu()
    for CPU specific initialization. interrupt_init_cpu()
    should set decrementer_count to appropriate value. If
    CPU resets decrementer automatically after interrupt
    (ppc4xx) it should set decrementer_count to zero.
    timer_interrupt() calls timer_interrupt_cpu() for CPU
    specific handling. If board has watchdog / status_led
    / other_activity_monitor it works automatically from
    general timer_interrupt().

Board initialization settings:

During Initialization u-boot calls a number of board specific functions to allow the preparation of board specific prerequisites, e.g. pin setup before drivers are initialized. To enable these callbacks the following configuration macros have to be defined. Currently this is architecture specific, so please check arch/your_architecture/lib/board.c typically in board_init_f() and board_init_r().

• CONFIG_BOARD_EARLY_INIT_F: Call board_early_init_f()
• CONFIG_BOARD_EARLY_INIT_R: Call board_early_init_r()
• CONFIG_BOARD_LATE_INIT: Call board_late_init()

Configuration Settings:

• MEM_SUPPORT_64BIT_DATA: Defined automatically if compiled as 64-bit.

    Optionally it can be defined to support 64-bit memory commands.

• CONFIG_SYS_LONGHELP: Defined when you want long help messages included;

    undefine this when you're short of memory.

• CONFIG_SYS_HELP_CMD_WIDTH: Defined when you want to override the default

    width of the commands listed in the 'help' command output.

• CONFIG_SYS_PROMPT: This is what U-Boot prints on the console to

    prompt for user input.

• CONFIG_SYS_BAUDRATE_TABLE:

    List of legal baudrate settings for this board.

• CONFIG_SYS_MEM_RESERVE_SECURE

    Only implemented for ARMv8 for now.
    If defined, the size of CONFIG_SYS_MEM_RESERVE_SECURE memory
    is substracted from total RAM and won't be reported to OS.
    This memory can be used as secure memory. A variable
    gd->arch.secure_ram is used to track the location. In systems
    the RAM base is not zero, or RAM is divided into banks,
    this variable needs to be recalcuated to get the address.

• CONFIG_SYS_LOADS_BAUD_CHANGE:

    Enable temporary baudrate change while serial download

• CONFIG_SYS_SDRAM_BASE:

    Physical start address of SDRAM. _Must_ be 0 here.

• CONFIG_SYS_FLASH_BASE:

    Physical start address of Flash memory.

• CONFIG_SYS_MONITOR_LEN:

    Size of memory reserved for monitor code, used to
    determine _at_compile_time_ (!) if the environment is
    embedded within the U-Boot image, or in a separate
    flash sector.

• CONFIG_SYS_MALLOC_LEN:

    Size of DRAM reserved for malloc() use.

• CONFIG_SYS_MALLOC_F_LEN

    Size of the malloc() pool for use before relocation. If
    this is defined, then a very simple malloc() implementation
    will become available before relocation. The address is just
    below the global data, and the stack is moved down to make
    space.
  
    This feature allocates regions with increasing addresses
    within the region. calloc() is supported, but realloc()
    is not available. free() is supported but does nothing.
    The memory will be freed (or in fact just forgotten) when
    U-Boot relocates itself.

• CONFIG_SYS_MALLOC_SIMPLE

    Provides a simple and small malloc() and calloc() for those
    boards which do not use the full malloc in SPL (which is
    enabled with CONFIG_SYS_SPL_MALLOC).

• CONFIG_SYS_NONCACHED_MEMORY:

    Size of non-cached memory area. This area of memory will be
    typically located right below the malloc() area and mapped
    uncached in the MMU. This is useful for drivers that would
    otherwise require a lot of explicit cache maintenance. For
    some drivers it's also impossible to properly maintain the
    cache. For example if the regions that need to be flushed
    are not a multiple of the cache-line size, *and* padding
    cannot be allocated between the regions to align them (i.e.
    if the HW requires a contiguous array of regions, and the
    size of each region is not cache-aligned), then a flush of
    one region may result in overwriting data that hardware has
    written to another region in the same cache-line. This can
    happen for example in network drivers where descriptors for
    buffers are typically smaller than the CPU cache-line (e.g.
    16 bytes vs. 32 or 64 bytes).
  
    Non-cached memory is only supported on 32-bit ARM at present.

• CONFIG_SYS_BOOTMAPSZ:

    Maximum size of memory mapped by the startup code of
    the Linux kernel; all data that must be processed by
    the Linux kernel (bd_info, boot arguments, FDT blob if
    used) must be put below this limit, unless "bootm_low"
    environment variable is defined and non-zero. In such case
    all data for the Linux kernel must be between "bootm_low"
    and "bootm_low" + CONFIG_SYS_BOOTMAPSZ.     The environment
    variable "bootm_mapsize" will override the value of
    CONFIG_SYS_BOOTMAPSZ.  If CONFIG_SYS_BOOTMAPSZ is undefined,
    then the value in "bootm_size" will be used instead.

• CONFIG_SYS_BOOT_GET_CMDLINE:

    Enables allocating and saving kernel cmdline in space between
    "bootm_low" and "bootm_low" + BOOTMAPSZ.

• CONFIG_SYS_BOOT_GET_KBD:

    Enables allocating and saving a kernel copy of the bd_info in
    space between "bootm_low" and "bootm_low" + BOOTMAPSZ.

• CONFIG_SYS_FLASH_PROTECTION

    If defined, hardware flash sectors protection is used
    instead of U-Boot software protection.

• CONFIG_SYS_FLASH_CFI:

    Define if the flash driver uses extra elements in the
    common flash structure for storing flash geometry.

• CONFIG_FLASH_CFI_DRIVER

    This option also enables the building of the cfi_flash driver
    in the drivers directory

• CONFIG_FLASH_CFI_MTD

    This option enables the building of the cfi_mtd driver
    in the drivers directory. The driver exports CFI flash
    to the MTD layer.

• CONFIG_SYS_FLASH_USE_BUFFER_WRITE

    Use buffered writes to flash.

• CONFIG_FLASH_SPANSION_S29WS_N

    s29ws-n MirrorBit flash has non-standard addresses for buffered
    write commands.

• CONFIG_FLASH_SHOW_PROGRESS

    If defined (must be an integer), print out countdown
    digits and dots.  Recommended value: 45 (9..1) for 80
    column displays, 15 (3..1) for 40 column displays.

• CONFIG_FLASH_VERIFY

    If defined, the content of the flash (destination) is compared
    against the source after the write operation. An error message
    will be printed when the contents are not identical.
    Please note that this option is useless in nearly all cases,
    since such flash programming errors usually are detected earlier
    while unprotecting/erasing/programming. Please only enable
    this option if you really know what you are doing.

• CONFIG_ENV_FLAGS_LIST_DEFAULT

• CONFIG_ENV_FLAGS_LIST_STATIC Enable validation of the values given to environment variables when calling env set. Variables can be restricted to only decimal, hexadecimal, or boolean. If CONFIG_CMD_NET is also defined, the variables can also be restricted to IP address or MAC address.

  The format of the list is:

    type_attribute = [s|d|x|b|i|m]
    access_attribute = [a|r|o|c]
    attributes = type_attribute[access_attribute]
    entry = variable_name[:attributes]
    list = entry[,list]

  The type attributes are:

    s - String (default)
    d - Decimal
    x - Hexadecimal
    b - Boolean ([1yYtT|0nNfF])
    i - IP address
    m - MAC address

  The access attributes are:

    a - Any (default)
    r - Read-only
    o - Write-once
    c - Change-default

  • CONFIG_ENV_FLAGS_LIST_DEFAULT Define this to a list (string) to define the “.flags” environment variable in the default or embedded environment.

  • CONFIG_ENV_FLAGS_LIST_STATIC Define this to a list (string) to define validation that should be done if an entry is not found in the “.flags” environment variable. To override a setting in the static list, simply add an entry for the same variable name to the “.flags” variable.

  If CONFIG_REGEX is defined, the variable_name above is evaluated as a regular expression. This allows multiple variables to define the same flags without explicitly listing them for each variable.

The following definitions that deal with the placement and management of environment data (variable area); in general, we support the following configurations:

• CONFIG_BUILD_ENVCRC:

  Builds up envcrc with the target environment so that external utils may easily extract it and embed it in final U-Boot images.

BE CAREFUL! The first access to the environment happens quite early in U-Boot initialization (when we try to get the setting of for the console baudrate). You MUST have mapped your NVRAM area then, or U-Boot will hang.

Please note that even with NVRAM we still use a copy of the environment in RAM: we could work on NVRAM directly, but we want to keep settings there always unmodified except somebody uses “saveenv” to save the current settings.

BE CAREFUL! For some special cases, the local device can not use “saveenv” command. For example, the local device will get the environment stored in a remote NOR flash by SRIO or PCIE link, but it can not erase, write this NOR flash by SRIO or PCIE interface.

• CONFIG_NAND_ENV_DST

  Defines address in RAM to which the nand_spl code should copy the environment. If redundant environment is used, it will be copied to CONFIG_NAND_ENV_DST + CONFIG_ENV_SIZE.

Please note that the environment is read-only until the monitor has been relocated to RAM and a RAM copy of the environment has been created; also, when using EEPROM you will have to use env_get_f() until then to read environment variables.

The environment is protected by a CRC32 checksum. Before the monitor is relocated into RAM, as a result of a bad CRC you will be working with the compiled-in default environment - silently!!! [This is necessary, because the first environment variable we need is the “baudrate” setting for the console - if we have a bad CRC, we don’t have any device yet where we could complain.]

Note: once the monitor has been relocated, then it will complain if the default environment is used; a new CRC is computed as soon as you use the “saveenv” command to store a valid environment.

• CONFIG_SYS_FAULT_MII_ADDR:

    MII address of the PHY to check for the Ethernet link state.

• CONFIG_NS16550_MIN_FUNCTIONS:

    Define this if you desire to only have use of the NS16550_init
    and NS16550_putc functions for the serial driver located at
    drivers/serial/ns16550.c.  This option is useful for saving
    space for already greatly restricted images, including but not
    limited to NAND_SPL configurations.

• CONFIG_DISPLAY_BOARDINFO

    Display information about the board that U-Boot is running on
    when U-Boot starts up. The board function checkboard() is called
    to do this.

• CONFIG_DISPLAY_BOARDINFO_LATE

    Similar to the previous option, but display this information
    later, once stdio is running and output goes to the LCD, if
    present.

Low Level (hardware related) configuration options:

• CONFIG_SYS_CACHELINE_SIZE:

    Cache Line Size of the CPU.

• CONFIG_SYS_CCSRBAR_DEFAULT:

    Default (power-on reset) physical address of CCSR on Freescale
    PowerPC SOCs.

• CONFIG_SYS_CCSRBAR:

    Virtual address of CCSR.  On a 32-bit build, this is typically
    the same value as CONFIG_SYS_CCSRBAR_DEFAULT.

• CONFIG_SYS_CCSRBAR_PHYS:

    Physical address of CCSR.  CCSR can be relocated to a new
    physical address, if desired.  In this case, this macro should
    be set to that address.     Otherwise, it should be set to the
    same value as CONFIG_SYS_CCSRBAR_DEFAULT.  For example, CCSR
    is typically relocated on 36-bit builds.  It is recommended
    that this macro be defined via the _HIGH and _LOW macros:
  
    #define CONFIG_SYS_CCSRBAR_PHYS ((CONFIG_SYS_CCSRBAR_PHYS_HIGH
        * 1ull) << 32 | CONFIG_SYS_CCSRBAR_PHYS_LOW)

• CONFIG_SYS_CCSRBAR_PHYS_HIGH:

    Bits 33-36 of CONFIG_SYS_CCSRBAR_PHYS.    This value is typically
    either 0 (32-bit build) or 0xF (36-bit build).    This macro is
    used in assembly code, so it must not contain typecasts or
    integer size suffixes (e.g. "ULL").

• CONFIG_SYS_CCSRBAR_PHYS_LOW:

    Lower 32-bits of CONFIG_SYS_CCSRBAR_PHYS.  This macro is
    used in assembly code, so it must not contain typecasts or
    integer size suffixes (e.g. "ULL").

• CONFIG_SYS_IMMR: Physical address of the Internal Memory.

    DO NOT CHANGE unless you know exactly what you're
    doing! (11-4) [MPC8xx systems only]

• CONFIG_SYS_INIT_RAM_ADDR:

    Start address of memory area that can be used for
    initial data and stack; please note that this must be
    writable memory that is working WITHOUT special
    initialization, i. e. you CANNOT use normal RAM which
    will become available only after programming the
    memory controller and running certain initialization
    sequences.
  
    U-Boot uses the following memory types:
    - MPC8xx: IMMR (internal memory of the CPU)

• CONFIG_SYS_SCCR: System Clock and reset Control Register (15-27)

• CONFIG_SYS_OR_TIMING_SDRAM:

    SDRAM timing

• CONFIG_SYS_MAMR_PTA:

    periodic timer for refresh

• CONFIG_SYS_SRIO:

    Chip has SRIO or not

• CONFIG_SRIO1:

    Board has SRIO 1 port available

• CONFIG_SRIO2:

    Board has SRIO 2 port available

• CONFIG_SRIO_PCIE_BOOT_MASTER

    Board can support master function for Boot from SRIO and PCIE

• CONFIG_SYS_SRIOn_MEM_VIRT:

    Virtual Address of SRIO port 'n' memory region

• CONFIG_SYS_SRIOn_MEM_PHYxS:

    Physical Address of SRIO port 'n' memory region

• CONFIG_SYS_SRIOn_MEM_SIZE:

    Size of SRIO port 'n' memory region

• CONFIG_SYS_NAND_BUSWIDTH_16BIT

    Defined to tell the NAND controller that the NAND chip is using
    a 16 bit bus.
    Not all NAND drivers use this symbol.
    Example of drivers that use it:
    - drivers/mtd/nand/raw/ndfc.c
    - drivers/mtd/nand/raw/mxc_nand.c

• CONFIG_SYS_NDFC_EBC0_CFG

    Sets the EBC0_CFG register for the NDFC. If not defined
    a default value will be used.

• CONFIG_SPD_EEPROM

    Get DDR timing information from an I2C EEPROM. Common
    with pluggable memory modules such as SODIMMs

  SPD_EEPROM_ADDRESS

    I2C address of the SPD EEPROM

• CONFIG_SYS_SPD_BUS_NUM

    If SPD EEPROM is on an I2C bus other than the first
    one, specify here. Note that the value must resolve
    to something your driver can deal with.

• CONFIG_FSL_DDR_INTERACTIVE

    Enable interactive DDR debugging. See doc/README.fsl-ddr.

• CONFIG_FSL_DDR_SYNC_REFRESH

    Enable sync of refresh for multiple controllers.

• CONFIG_FSL_DDR_BIST

    Enable built-in memory test for Freescale DDR controllers.

• CONFIG_RMII

    Enable RMII mode for all FECs.
    Note that this is a global option, we can't
    have one FEC in standard MII mode and another in RMII mode.

• CONFIG_CRC32_VERIFY

    Add a verify option to the crc32 command.
    The syntax is:
  
    => crc32 -v <address> <count> <crc32>
  
    Where address/count indicate a memory area
    and crc32 is the correct crc32 which the
    area should have.

• CONFIG_LOOPW

    Add the "loopw" memory command. This only takes effect if
    the memory commands are activated globally (CONFIG_CMD_MEMORY).

• CONFIG_CMD_MX_CYCLIC

    Add the "mdc" and "mwc" memory commands. These are cyclic
    "md/mw" commands.
    Examples:
  
    => mdc.b 10 4 500
    This command will print 4 bytes (10,11,12,13) each 500 ms.
  
    => mwc.l 100 12345678 10
    This command will write 12345678 to address 100 all 10 ms.
  
    This only takes effect if the memory commands are activated
    globally (CONFIG_CMD_MEMORY).

• CONFIG_SPL_BUILD

    Set when the currently-running compilation is for an artifact
    that will end up in the SPL (as opposed to the TPL or U-Boot
    proper). Code that needs stage-specific behavior should check
    this.

• CONFIG_TPL_BUILD

    Set when the currently-running compilation is for an artifact
    that will end up in the TPL (as opposed to the SPL or U-Boot
    proper). Code that needs stage-specific behavior should check
    this.

• CONFIG_ARCH_MAP_SYSMEM

    Generally U-Boot (and in particular the md command) uses
    effective address. It is therefore not necessary to regard
    U-Boot address as virtual addresses that need to be translated
    to physical addresses. However, sandbox requires this, since
    it maintains its own little RAM buffer which contains all
    addressable memory. This option causes some memory accesses
    to be mapped through map_sysmem() / unmap_sysmem().

• CONFIG_X86_RESET_VECTOR

    If defined, the x86 reset vector code is included. This is not
    needed when U-Boot is running from Coreboot.

• CONFIG_SYS_NAND_NO_SUBPAGE_WRITE

    Option to disable subpage write in NAND driver
    driver that uses this:
    drivers/mtd/nand/raw/davinci_nand.c

Freescale QE/FMAN Firmware Support:

The Freescale QUICCEngine (QE) and Frame Manager (FMAN) both support the loading of “firmware”, which is encoded in the QE firmware binary format. This firmware often needs to be loaded during U-Boot booting, so macros are used to identify the storage device (NOR flash, SPI, etc) and the address within that device.

• CONFIG_SYS_FMAN_FW_ADDR The address in the storage device where the FMAN microcode is located. The meaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macro is also specified.

• CONFIG_SYS_QE_FW_ADDR The address in the storage device where the QE microcode is located. The meaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macro is also specified.

• CONFIG_SYS_QE_FMAN_FW_LENGTH The maximum possible size of the firmware. The firmware binary format has a field that specifies the actual size of the firmware, but it might not be possible to read any part of the firmware unless some local storage is allocated to hold the entire firmware first.

• CONFIG_SYS_QE_FMAN_FW_IN_NOR Specifies that QE/FMAN firmware is located in NOR flash, mapped as normal addressable memory via the LBC. CONFIG_SYS_FMAN_FW_ADDR is the virtual address in NOR flash.

• CONFIG_SYS_QE_FMAN_FW_IN_NAND Specifies that QE/FMAN firmware is located in NAND flash. CONFIG_SYS_FMAN_FW_ADDR is the offset within NAND flash.

• CONFIG_SYS_QE_FMAN_FW_IN_MMC Specifies that QE/FMAN firmware is located on the primary SD/MMC device. CONFIG_SYS_FMAN_FW_ADDR is the byte offset on that device.

• CONFIG_SYS_QE_FMAN_FW_IN_REMOTE Specifies that QE/FMAN firmware is located in the remote (master) memory space. CONFIG_SYS_FMAN_FW_ADDR is a virtual address which can be mapped from slave TLB->slave LAW->slave SRIO or PCIE outbound window->master inbound window->master LAW->the ucode address in master’s memory space.

Freescale Layerscape Management Complex Firmware Support:

The Freescale Layerscape Management Complex (MC) supports the loading of “firmware”. This firmware often needs to be loaded during U-Boot booting, so macros are used to identify the storage device (NOR flash, SPI, etc) and the address within that device.

• CONFIG_FSL_MC_ENET Enable the MC driver for Layerscape SoCs.

Freescale Layerscape Debug Server Support:

The Freescale Layerscape Debug Server Support supports the loading of “Debug Server firmware” and triggering SP boot-rom. This firmware often needs to be loaded during U-Boot booting.

• CONFIG_SYS_MC_RSV_MEM_ALIGN Define alignment of reserved memory MC requires

Reproducible builds

In order to achieve reproducible builds, timestamps used in the U-Boot build process have to be set to a fixed value.

This is done using the SOURCE_DATE_EPOCH environment variable. SOURCE_DATE_EPOCH is to be set on the build host’s shell, not as a configuration option for U-Boot or an environment variable in U-Boot.

SOURCE_DATE_EPOCH should be set to a number of seconds since the epoch, in UTC.

Building the Software:

Building U-Boot has been tested in several native build environments and in many different cross environments. Of course we cannot support all possibly existing versions of cross development tools in all (potentially obsolete) versions. In case of tool chain problems we recommend to use the ELDK (see https://www.denx.de/wiki/DULG/ELDK) which is extensively used to build and test U-Boot.

If you are not using a native environment, it is assumed that you have GNU cross compiling tools available in your path. In this case, you must set the environment variable CROSS_COMPILE in your shell. Note that no changes to the Makefile or any other source files are necessary. For example using the ELDK on a 4xx CPU, please enter:

$ CROSS_COMPILE=ppc_4xx-
$ export CROSS_COMPILE

U-Boot is intended to be simple to build. After installing the sources you must configure U-Boot for one specific board type. This is done by typing:

make NAME_defconfig

where “NAME_defconfig” is the name of one of the existing configu- rations; see configs/*_defconfig for supported names.

Note: for some boards special configuration names may exist; check if additional information is available from the board vendor; for instance, the TQM823L systems are available without (standard) or with LCD support. You can select such additional “features” when choosing the configuration, i. e.

  make TQM823L_defconfig
- will configure for a plain TQM823L, i. e. no LCD support

  make TQM823L_LCD_defconfig
- will configure for a TQM823L with U-Boot console on LCD

  etc.

Finally, type “make all”, and you should get some working U-Boot images ready for download to / installation on your system:

• “u-boot.bin” is a raw binary image
• “u-boot” is an image in ELF binary format
• “u-boot.srec” is in Motorola S-Record format

By default the build is performed locally and the objects are saved in the source directory. One of the two methods can be used to change this behavior and build U-Boot to some external directory:

1. Add O= to the make command line invocations:

   make O=/tmp/build distclean make O=/tmp/build NAME_defconfig make O=/tmp/build all

2. Set environment variable KBUILD_OUTPUT to point to the desired location:

   export KBUILD_OUTPUT=/tmp/build make distclean make NAME_defconfig make all

Note that the command line “O=” setting overrides the KBUILD_OUTPUT environment variable.

User specific CPPFLAGS, AFLAGS and CFLAGS can be passed to the compiler by setting the according environment variables KCPPFLAGS, KAFLAGS and KCFLAGS. For example to treat all compiler warnings as errors:

make KCFLAGS=-Werror

Please be aware that the Makefiles assume you are using GNU make, so for instance on NetBSD you might need to use “gmake” instead of native “make”.

If the system board that you have is not listed, then you will need to port U-Boot to your hardware platform. To do this, follow these steps:

1. Create a new directory to hold your board specific code. Add any files you need. In your board directory, you will need at least the “Makefile” and a “.c”.
2. Create a new configuration file “include/configs/.h” for your board.
3. If you’re porting U-Boot to a new CPU, then also create a new directory to hold your CPU specific code. Add any files you need.
4. Run “make _defconfig” with your new name.
5. Type “make”, and you should get a working “u-boot.srec” file to be installed on your target system.
6. Debug and solve any problems that might arise. [Of course, this last step is much harder than it sounds.]

Testing of U-Boot Modifications, Ports to New Hardware, etc.:

If you have modified U-Boot sources (for instance added a new board or support for new devices, a new CPU, etc.) you are expected to provide feedback to the other developers. The feedback normally takes the form of a “patch”, i.e. a context diff against a certain (latest official or latest in the git repository) version of U-Boot sources.

But before you submit such a patch, please verify that your modifi- cation did not break existing code. At least make sure that ALL of the supported boards compile WITHOUT ANY compiler warnings. To do so, just run the buildman script (tools/buildman/buildman), which will configure and build U-Boot for ALL supported system. Be warned, this will take a while. Please see the buildman README, or run ‘buildman -H’ for documentation.

See also “U-Boot Porting Guide” below.

Monitor Commands - Overview:

go - start application at address ‘addr’ run - run commands in an environment variable bootm - boot application image from memory bootp - boot image via network using BootP/TFTP protocol bootz - boot zImage from memory tftpboot- boot image via network using TFTP protocol and env variables “ipaddr” and “serverip” (and eventually “gatewayip”) tftpput - upload a file via network using TFTP protocol rarpboot- boot image via network using RARP/TFTP protocol diskboot- boot from IDE devicebootd - boot default, i.e., run ‘bootcmd’ loads - load S-Record file over serial line loadb - load binary file over serial line (kermit mode) loadm - load binary blob from source address to destination address md - memory display mm - memory modify (auto-incrementing) nm - memory modify (constant address) mw - memory write (fill) ms - memory search cp - memory copy cmp - memory compare crc32 - checksum calculation i2c - I2C sub-system sspi - SPI utility commands base - print or set address offset printenv- print environment variables pwm - control pwm channels setenv - set environment variables saveenv - save environment variables to persistent storage protect - enable or disable FLASH write protection erase - erase FLASH memory flinfo - print FLASH memory information nand - NAND memory operations (see doc/README.nand) bdinfo - print Board Info structure iminfo - print header information for application image coninfo - print console devices and informations ide - IDE sub-system loop - infinite loop on address range loopw - infinite write loop on address range mtest - simple RAM test icache - enable or disable instruction cache dcache - enable or disable data cache reset - Perform RESET of the CPU echo - echo args to console version - print monitor version help - print online help ? - alias for ‘help’

Monitor Commands - Detailed Description:

TODO.

For now: just type “help “.

Note for Redundant Ethernet Interfaces:

Some boards come with redundant Ethernet interfaces; U-Boot supports such configurations and is capable of automatic selection of a “working” interface when needed. MAC assignment works as follows:

Network interfaces are numbered eth0, eth1, eth2, … Corresponding MAC addresses can be stored in the environment as “ethaddr” (=>eth0), “eth1addr” (=>eth1), “eth2addr”, …

If the network interface stores some valid MAC address (for instance in SROM), this is used as default address if there is NO correspon- ding setting in the environment; if the corresponding environment variable is set, this overrides the settings in the card; that means:

o If the SROM has a valid MAC address, and there is no address in the environment, the SROM’s address is used.

o If there is no valid address in the SROM, and a definition in the environment exists, then the value from the environment variable is used.

o If both the SROM and the environment contain a MAC address, and both addresses are the same, this MAC address is used.

o If both the SROM and the environment contain a MAC address, and the addresses differ, the value from the environment is used and a warning is printed.

o If neither SROM nor the environment contain a MAC address, an error is raised. If CONFIG_NET_RANDOM_ETHADDR is defined, then in this case a random, locally-assigned MAC is used.

If Ethernet drivers implement the ‘write_hwaddr’ function, valid MAC addresses will be programmed into hardware as part of the initialization process. This may be skipped by setting the appropriate ‘ethmacskip’ environment variable. The naming convention is as follows: “ethmacskip” (=>eth0), “eth1macskip” (=>eth1) etc.

Image Formats:

U-Boot is capable of booting (and performing other auxiliary operations on) images in two formats:

New uImage format (FIT)

Flexible and powerful format based on Flattened Image Tree – FIT (similar to Flattened Device Tree). It allows the use of images with multiple components (several kernels, ramdisks, etc.), with contents protected by SHA1, MD5 or CRC32. More details are found in the doc/uImage.FIT directory.

Old uImage format

Old image format is based on binary files which can be basically anything, preceded by a special header; see the definitions in include/image.h for details; basically, the header defines the following image properties:

• Target Operating System (Provisions for OpenBSD, NetBSD, FreeBSD, 4.4BSD, Linux, SVR4, Esix, Solaris, Irix, SCO, Dell, NCR, VxWorks, LynxOS, pSOS, QNX, RTEMS, INTEGRITY; Currently supported: Linux, NetBSD, VxWorks, QNX, RTEMS, INTEGRITY).
• Target CPU Architecture (Provisions for Alpha, ARM, Intel x86, IA64, MIPS, Nios II, PowerPC, IBM S390, SuperH, Sparc, Sparc 64 Bit; Currently supported: ARM, Intel x86, MIPS, Nios II, PowerPC).
• Compression Type (uncompressed, gzip, bzip2)
• Load Address
• Entry Point
• Image Name
• Image Timestamp

The header is marked by a special Magic Number, and both the header and the data portions of the image are secured against corruption by CRC32 checksums.

Linux Support:

Although U-Boot should support any OS or standalone application easily, the main focus has always been on Linux during the design of U-Boot.

U-Boot includes many features that so far have been part of some special “boot loader” code within the Linux kernel. Also, any “initrd” images to be used are no longer part of one big Linux image; instead, kernel and “initrd” are separate images. This implementation serves several purposes:

• the same features can be used for other OS or standalone applications (for instance: using compressed images to reduce the Flash memory footprint)

• it becomes much easier to port new Linux kernel versions because lots of low-level, hardware dependent stuff are done by U-Boot

• the same Linux kernel image can now be used with different “initrd” images; of course this also means that different kernel images can be run with the same “initrd”. This makes testing easier (you don’t have to build a new “zImage.initrd” Linux image when you just change a file in your “initrd”). Also, a field-upgrade of the software is easier now.

Linux HOWTO:

Porting Linux to U-Boot based systems:

U-Boot cannot save you from doing all the necessary modifications to configure the Linux device drivers for use with your target hardware (no, we don’t intend to provide a full virtual machine interface to Linux :-).

But now you can ignore ALL boot loader code (in arch/powerpc/mbxboot).

Just make sure your machine specific header file (for instance include/asm-ppc/tqm8xx.h) includes the same definition of the Board Information structure as we define in include/asm-/u-boot.h, and make sure that your definition of IMAP_ADDR uses the same value as your U-Boot configuration in CONFIG_SYS_IMMR.

Note that U-Boot now has a driver model, a unified model for drivers. If you are adding a new driver, plumb it into driver model. If there is no uclass available, you are encouraged to create one. See doc/driver-model.

Configuring the Linux kernel:

No specific requirements for U-Boot. Make sure you have some root device (initial ramdisk, NFS) for your target system.

Building a Linux Image:

With U-Boot, “normal” build targets like “zImage” or “bzImage” are not used. If you use recent kernel source, a new build target “uImage” will exist which automatically builds an image usable by U-Boot. Most older kernels also have support for a “pImage” target, which was introduced for our predecessor project PPCBoot and uses a 100% compatible format.

Example:

make TQM850L_defconfig
make oldconfig
make dep
make uImage

The “uImage” build target uses a special tool (in ‘tools/mkimage’) to encapsulate a compressed Linux kernel image with header information, CRC32 checksum etc. for use with U-Boot. This is what we are doing:

• build a standard “vmlinux” kernel image (in ELF binary format):

• convert the kernel into a raw binary image:

  ${CROSS_COMPILE}-objcopy -O binary \

             -R .note -R .comment \
             -S vmlinux linux.bin

• compress the binary image:

  gzip -9 linux.bin

• package compressed binary image for U-Boot:

  mkimage -A ppc -O linux -T kernel -C gzip \

    -a 0 -e 0 -n "Linux Kernel Image" \
    -d linux.bin.gz uImage

The “mkimage” tool can also be used to create ramdisk images for use with U-Boot, either separated from the Linux kernel image, or combined into one file. “mkimage” encapsulates the images with a 64 byte header containing information about target architecture, operating system, image type, compression method, entry points, time stamp, CRC32 checksums, etc.

“mkimage” can be called in two ways: to verify existing images and print the header information, or to build new images.

In the first form (with “-l” option) mkimage lists the information contained in the header of an existing U-Boot image; this includes checksum verification:

tools/mkimage -l image
  -l ==> list image header information

The second form (with “-d” option) is used to build a U-Boot image from a “data file” which is used as image payload:

tools/mkimage -A arch -O os -T type -C comp -a addr -e ep \
          -n name -d data_file image
  -A ==> set architecture to 'arch'
  -O ==> set operating system to 'os'
  -T ==> set image type to 'type'
  -C ==> set compression type 'comp'
  -a ==> set load address to 'addr' (hex)
  -e ==> set entry point to 'ep' (hex)
  -n ==> set image name to 'name'
  -d ==> use image data from 'datafile'

Right now, all Linux kernels for PowerPC systems use the same load address (0x00000000), but the entry point address depends on the kernel version:

• 2.2.x kernels have the entry point at 0x0000000C,
• 2.3.x and later kernels have the entry point at 0x00000000.

So a typical call to build a U-Boot image would read:

-> tools/mkimage -n '2.4.4 kernel for TQM850L' \
> -A ppc -O linux -T kernel -C gzip -a 0 -e 0 \
> -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz \
> examples/uImage.TQM850L
Image Name:   2.4.4 kernel for TQM850L
Created:      Wed Jul 19 02:34:59 2000
Image Type:   PowerPC Linux Kernel Image (gzip compressed)
Data Size:    335725 Bytes = 327.86 kB = 0.32 MB
Load Address: 0x00000000
Entry Point:  0x00000000

To verify the contents of the image (or check for corruption):

-> tools/mkimage -l examples/uImage.TQM850L
Image Name:   2.4.4 kernel for TQM850L
Created:      Wed Jul 19 02:34:59 2000
Image Type:   PowerPC Linux Kernel Image (gzip compressed)
Data Size:    335725 Bytes = 327.86 kB = 0.32 MB
Load Address: 0x00000000
Entry Point:  0x00000000

NOTE: for embedded systems where boot time is critical you can trade speed for memory and install an UNCOMPRESSED image instead: this needs more space in Flash, but boots much faster since it does not need to be uncompressed:

-> gunzip /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz
-> tools/mkimage -n '2.4.4 kernel for TQM850L' \
> -A ppc -O linux -T kernel -C none -a 0 -e 0 \
> -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux \
> examples/uImage.TQM850L-uncompressed
Image Name:   2.4.4 kernel for TQM850L
Created:      Wed Jul 19 02:34:59 2000
Image Type:   PowerPC Linux Kernel Image (uncompressed)
Data Size:    792160 Bytes = 773.59 kB = 0.76 MB
Load Address: 0x00000000
Entry Point:  0x00000000

Similar you can build U-Boot images from a ‘ramdisk.image.gz’ file when your kernel is intended to use an initial ramdisk:

-> tools/mkimage -n 'Simple Ramdisk Image' \
> -A ppc -O linux -T ramdisk -C gzip \
> -d /LinuxPPC/images/SIMPLE-ramdisk.image.gz examples/simple-initrd
Image Name:   Simple Ramdisk Image
Created:      Wed Jan 12 14:01:50 2000
Image Type:   PowerPC Linux RAMDisk Image (gzip compressed)
Data Size:    566530 Bytes = 553.25 kB = 0.54 MB
Load Address: 0x00000000
Entry Point:  0x00000000

The “dumpimage” tool can be used to disassemble or list the contents of images built by mkimage. See dumpimage’s help output (-h) for details.

Installing a Linux Image:

To downloading a U-Boot image over the serial (console) interface, you must convert the image to S-Record format:

objcopy -I binary -O srec examples/image examples/image.srec

The ‘objcopy’ does not understand the information in the U-Boot image header, so the resulting S-Record file will be relative to address 0x00000000. To load it to a given address, you need to specify the target address as ‘offset’ parameter with the ‘loads’ command.

Example: install the image to address 0x40100000 (which on the TQM8xxL is in the first Flash bank):

=> erase 40100000 401FFFFF

.......... done
Erased 8 sectors

=> loads 40100000
## Ready for S-Record download ...
~>examples/image.srec
1 2 3 4 5 6 7 8 9 10 11 12 13 ...
...
15989 15990 15991 15992
[file transfer complete]
[connected]
## Start Addr = 0x00000000

You can check the success of the download using the ‘iminfo’ command; this includes a checksum verification so you can be sure no data corruption happened:

=> imi 40100000

## Checking Image at 40100000 ...
   Image Name:     2.2.13 for initrd on TQM850L
   Image Type:     PowerPC Linux Kernel Image (gzip compressed)
   Data Size:     335725 Bytes = 327 kB = 0 MB
   Load Address: 00000000
   Entry Point:     0000000c
   Verifying Checksum ... OK

Boot Linux:

The “bootm” command is used to boot an application that is stored in memory (RAM or Flash). In case of a Linux kernel image, the contents of the “bootargs” environment variable is passed to the kernel as parameters. You can check and modify this variable using the “printenv” and “setenv” commands:

=> printenv bootargs
bootargs=root=/dev/ram

=> setenv bootargs root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2

=> printenv bootargs
bootargs=root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2

=> bootm 40020000
## Booting Linux kernel at 40020000 ...
   Image Name:     2.2.13 for NFS on TQM850L
   Image Type:     PowerPC Linux Kernel Image (gzip compressed)
   Data Size:     381681 Bytes = 372 kB = 0 MB
   Load Address: 00000000
   Entry Point:     0000000c
   Verifying Checksum ... OK
   Uncompressing Kernel Image ... OK
Linux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:35:17 MEST 2000
Boot arguments: root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
time_init: decrementer frequency = 187500000/60
Calibrating delay loop... 49.77 BogoMIPS
Memory: 15208k available (700k kernel code, 444k data, 32k init) [c0000000,c1000000]
...

If you want to boot a Linux kernel with initial RAM disk, you pass the memory addresses of both the kernel and the initrd image (PPBCOOT format!) to the “bootm” command:

=> imi 40100000 40200000

## Checking Image at 40100000 ...
   Image Name:     2.2.13 for initrd on TQM850L
   Image Type:     PowerPC Linux Kernel Image (gzip compressed)
   Data Size:     335725 Bytes = 327 kB = 0 MB
   Load Address: 00000000
   Entry Point:     0000000c
   Verifying Checksum ... OK

## Checking Image at 40200000 ...
   Image Name:     Simple Ramdisk Image
   Image Type:     PowerPC Linux RAMDisk Image (gzip compressed)
   Data Size:     566530 Bytes = 553 kB = 0 MB
   Load Address: 00000000
   Entry Point:     00000000
   Verifying Checksum ... OK

=> bootm 40100000 40200000
## Booting Linux kernel at 40100000 ...
   Image Name:     2.2.13 for initrd on TQM850L
   Image Type:     PowerPC Linux Kernel Image (gzip compressed)
   Data Size:     335725 Bytes = 327 kB = 0 MB
   Load Address: 00000000
   Entry Point:     0000000c
   Verifying Checksum ... OK
   Uncompressing Kernel Image ... OK
## Loading RAMDisk Image at 40200000 ...
   Image Name:     Simple Ramdisk Image
   Image Type:     PowerPC Linux RAMDisk Image (gzip compressed)
   Data Size:     566530 Bytes = 553 kB = 0 MB
   Load Address: 00000000
   Entry Point:     00000000
   Verifying Checksum ... OK
   Loading Ramdisk ... OK
Linux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:32:08 MEST 2000
Boot arguments: root=/dev/ram
time_init: decrementer frequency = 187500000/60
Calibrating delay loop... 49.77 BogoMIPS
...
RAMDISK: Compressed image found at block 0
VFS: Mounted root (ext2 filesystem).

bash#

Boot Linux and pass a flat device tree:

First, U-Boot must be compiled with the appropriate defines. See the section titled “Linux Kernel Interface” above for a more in depth explanation. The following is an example of how to start a kernel and pass an updated flat device tree:

=> print oftaddr oftaddr=0x300000 => print oft oft=oftrees/mpc8540ads.dtb => tftp $oftaddr $oft Speed: 1000, full duplex Using TSEC0 device TFTP from server 192.168.1.1; our IP address is 192.168.1.101 Filename ‘oftrees/mpc8540ads.dtb’. Load address: 0x300000 Loading: # done Bytes transferred = 4106 (100a hex) => tftp $loadaddr $bootfile Speed: 1000, full duplex Using TSEC0 device TFTP from server 192.168.1.1; our IP address is 192.168.1.2 Filename ‘uImage’. Load address: 0x200000 Loading:############ done Bytes transferred = 1029407 (fb51f hex) => print loadaddr loadaddr=200000 => print oftaddr oftaddr=0x300000 => bootm $loadaddr - $oftaddr

Booting image at 00200000 …

Image Name: Linux-2.6.17-dirty Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 1029343 Bytes = 1005.2 kB Load Address: 00000000 Entry Point: 00000000 Verifying Checksum … OK Uncompressing Kernel Image … OK Booting using flat device tree at 0x300000 Using MPC85xx ADS machine description Memory CAM mapping: CAM0=256Mb, CAM1=256Mb, CAM2=0Mb residual: 0Mb [snip]

More About U-Boot Image Types:

U-Boot supports the following image types:

“Standalone Programs” are directly runnable in the environment provided by U-Boot; it is expected that (if they behave well) you can continue to work in U-Boot after return from the Standalone Program. “OS Kernel Images” are usually images of some Embedded OS which will take over control completely. Usually these programs will install their own set of exception handlers, device drivers, set up the MMU, etc. - this means, that you cannot expect to re-enter U-Boot except by resetting the CPU. “RAMDisk Images” are more or less just data blocks, and their parameters (address, size) are passed to an OS kernel that is being started. “Multi-File Images” contain several images, typically an OS (Linux) kernel image and one or more data images like RAMDisks. This construct is useful for instance when you want to boot over the network using BOOTP etc., where the boot server provides just a single image file, but you want to get for instance an OS kernel and a RAMDisk image.

"Multi-File Images" start with a list of image sizes, each
image size (in bytes) specified by an "uint32_t" in network
byte order. This list is terminated by an "(uint32_t)0".
Immediately after the terminating 0 follow the images, one by
one, all aligned on "uint32_t" boundaries (size rounded up to
a multiple of 4 bytes).

“Firmware Images” are binary images containing firmware (like U-Boot or FPGA images) which usually will be programmed to flash memory.

“Script files” are command sequences that will be executed by U-Boot’s command interpreter; this feature is especially useful when you configure U-Boot to use a real shell (hush) as command interpreter.

Booting the Linux zImage:

On some platforms, it’s possible to boot Linux zImage. This is done using the “bootz” command. The syntax of “bootz” command is the same as the syntax of “bootm” command.

Note, defining the CONFIG_SUPPORT_RAW_INITRD allows user to supply kernel with raw initrd images. The syntax is slightly different, the address of the initrd must be augmented by it’s size, in the following format: “:“.

Standalone HOWTO:

One of the features of U-Boot is that you can dynamically load and run “standalone” applications, which can use some resources of U-Boot like console I/O functions or interrupt services.

Two simple examples are included with the sources:

“Hello World” Demo:

‘examples/hello_world.c’ contains a small “Hello World” Demo application; it is automatically compiled when you build U-Boot. It’s configured to run at address 0x00040004, so you can play with it like that:

=> loads
## Ready for S-Record download ...
~>examples/hello_world.srec
1 2 3 4 5 6 7 8 9 10 11 ...
[file transfer complete]
[connected]
## Start Addr = 0x00040004

=> go 40004 Hello World! This is a test.
## Starting application at 0x00040004 ...
Hello World
argc = 7
argv[0] = "40004"
argv[1] = "Hello"
argv[2] = "World!"
argv[3] = "This"
argv[4] = "is"
argv[5] = "a"
argv[6] = "test."
argv[7] = "<NULL>"
Hit any key to exit ...

## Application terminated, rc = 0x0

Another example, which demonstrates how to register a CPM interrupt handler with the U-Boot code, can be found in ‘examples/timer.c’. Here, a CPM timer is set up to generate an interrupt every second. The interrupt service routine is trivial, just printing a ‘.’ character, but this is just a demo program. The application can be controlled by the following keys:

? - print current values og the CPM Timer registers
b - enable interrupts and start timer
e - stop timer and disable interrupts
q - quit application

=> loads
## Ready for S-Record download ...
~>examples/timer.srec
1 2 3 4 5 6 7 8 9 10 11 ...
[file transfer complete]
[connected]
## Start Addr = 0x00040004

=> go 40004
## Starting application at 0x00040004 ...
TIMERS=0xfff00980
Using timer 1
  tgcr @ 0xfff00980, tmr @ 0xfff00990, trr @ 0xfff00994, tcr @ 0xfff00998, tcn @ 0xfff0099c, ter @ 0xfff009b0

Hit ‘b’: [q, b, e, ?] Set interval 1000000 us Enabling timer Hit ‘?’: [q, b, e, ?] …….. tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0xef6, ter=0x0 Hit ‘?’: [q, b, e, ?] . tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x2ad4, ter=0x0 Hit ‘?’: [q, b, e, ?] . tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x1efc, ter=0x0 Hit ‘?’: [q, b, e, ?] . tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x169d, ter=0x0 Hit ‘e’: [q, b, e, ?] …Stopping timer Hit ‘q’: [q, b, e, ?] ## Application terminated, rc = 0x0

Minicom warning:

Over time, many people have reported problems when trying to use the “minicom” terminal emulation program for serial download. I (wd) consider minicom to be broken, and recommend not to use it. Under Unix, I recommend to use C-Kermit for general purpose use (and especially for kermit binary protocol download (“loadb” command), and use “cu” for S-Record download (“loads” command). See https://www.denx.de/wiki/view/DULG/SystemSetup#Section_4.3. for help with kermit.

Nevertheless, if you absolutely want to use it try adding this configuration to your “File transfer protocols” section:

   Name       Program            Name U/D FullScr IO-Red. Multi
X  kermit  /usr/bin/kermit -i -l %l -s     Y    U       Y       N      N
Y  kermit  /usr/bin/kermit -i -l %l -r     N    D       Y       N      N

NetBSD Notes:

Starting at version 0.9.2, U-Boot supports NetBSD both as host (build U-Boot) and target system (boots NetBSD/mpc8xx).

Building requires a cross environment; it is known to work on NetBSD/i386 with the cross-powerpc-netbsd-1.3 package (you will also need gmake since the Makefiles are not compatible with BSD make). Note that the cross-powerpc package does not install include files; attempting to build U-Boot will fail because <machine/ansi.h> is missing. This file has to be installed and patched manually:

# cd /usr/pkg/cross/powerpc-netbsd/include
# mkdir powerpc
# ln -s powerpc machine
# cp /usr/src/sys/arch/powerpc/include/ansi.h powerpc/ansi.h
# ${EDIT} powerpc/ansi.h    ## must remove __va_list, _BSD_VA_LIST

Native builds don’t work due to incompatibilities between native and U-Boot include files.

Booting assumes that (the first part of) the image booted is a stage-2 loader which in turn loads and then invokes the kernel proper. Loader sources will eventually appear in the NetBSD source tree (probably in sys/arc/mpc8xx/stand/u-boot_stage2/); in the meantime, see ftp://ftp.denx.de/pub/u-boot/ppcboot_stage2.tar.gz

Implementation Internals:

The following is not intended to be a complete description of every implementation detail. However, it should help to understand the inner workings of U-Boot and make it easier to port it to custom hardware.

Initial Stack, Global Data:

The implementation of U-Boot is complicated by the fact that U-Boot starts running out of ROM (flash memory), usually without access to system RAM (because the memory controller is not initialized yet). This means that we don’t have writable Data or BSS segments, and BSS is not initialized as zero. To be able to get a C environment working at all, we have to allocate at least a minimal stack. Implementation options for this are defined and restricted by the CPU used: Some CPU models provide on-chip memory (like the IMMR area on MPC8xx and MPC826x processors), on others (parts of) the data cache can be locked as (mis-) used as memory, etc.

Chris Hallinan posted a good summary of these issues to the
U-Boot mailing list:

Subject: RE: [U-Boot-Users] RE: More On Memory Bank x (nothingness)?
From: "Chris Hallinan" <clh@net1plus.com>
Date: Mon, 10 Feb 2003 16:43:46 -0500 (22:43 MET)
...

Correct me if I'm wrong, folks, but the way I understand it
is this: Using DCACHE as initial RAM for Stack, etc, does not
require any physical RAM backing up the cache. The cleverness
is that the cache is being used as a temporary supply of
necessary storage before the SDRAM controller is setup. It's
beyond the scope of this list to explain the details, but you
can see how this works by studying the cache architecture and
operation in the architecture and processor-specific manuals.

OCM is On Chip Memory, which I believe the 405GP has 4K. It
is another option for the system designer to use as an
initial stack/RAM area prior to SDRAM being available. Either
option should work for you. Using CS 4 should be fine if your
board designers haven't used it for something that would
cause you grief during the initial boot! It is frequently not
used.

CONFIG_SYS_INIT_RAM_ADDR should be somewhere that won't interfere
with your processor/board/system design. The default value
you will find in any recent u-boot distribution in
walnut.h should work for you. I'd set it to a value larger
than your SDRAM module. If you have a 64MB SDRAM module, set
it above 400_0000. Just make sure your board has no resources
that are supposed to respond to that address! That code in
start.S has been around a while and should work as is when
you get the config right.

-Chris Hallinan
DS4.COM, Inc.

It is essential to remember this, since it has some impact on the C code for the initialization procedures:

• Initialized global data (data segment) is read-only. Do not attempt to write it.

• Do not use any uninitialized global data (or implicitly initialized as zero data - BSS segment) at all - this is undefined, initiali- zation is performed later (when relocating to RAM).

• Stack space is very limited. Avoid big data buffers or things like that.

Having only the stack as writable memory limits means we cannot use normal global data to share information between the code. But it turned out that the implementation of U-Boot can be greatly simplified by making a global data structure (gd_t) available to all functions. We could pass a pointer to this data as argument to all functions, but this would bloat the code. Instead we use a feature of the GCC compiler (Global Register Variables) to share the data: we place a pointer (gd) to the global data into a register which we reserve for this purpose.

When choosing a register for such a purpose we are restricted by the relevant (E)ABI specifications for the current architecture, and by GCC’s implementation.

For PowerPC, the following registers have specific use: R1: stack pointer R2: reserved for system use R3-R4: parameter passing and return values R5-R10: parameter passing R13: small data area pointer R30: GOT pointer R31: frame pointer

(U-Boot also uses R12 as internal GOT pointer. r12
is a volatile register so r12 needs to be reset when
going back and forth between asm and C)

==> U-Boot will use R2 to hold a pointer to the global data

Note: on PPC, we could use a static initializer (since the
address of the global data structure is known at compile time),
but it turned out that reserving a register results in somewhat
smaller code - although the code savings are not that big (on
average for all boards 752 bytes for the whole U-Boot image,
624 text + 127 data).

On ARM, the following registers are used:

R0:    function argument word/integer result
R1-R3:    function argument word
R9:    platform specific
R10:    stack limit (used only if stack checking is enabled)
R11:    argument (frame) pointer
R12:    temporary workspace
R13:    stack pointer
R14:    link register
R15:    program counter

==> U-Boot will use R9 to hold a pointer to the global data

Note: on ARM, only R_ARM_RELATIVE relocations are supported.

On Nios II, the ABI is documented here: https://www.altera.com/literature/hb/nios2/n2cpu_nii51016.pdf

==> U-Boot will use gp to hold a pointer to the global data

Note: on Nios II, we give "-G0" option to gcc and don't use gp
to access small data sections, so gp is free.

On RISC-V, the following registers are used:

x0: hard-wired zero (zero)
x1: return address (ra)
x2:    stack pointer (sp)
x3:    global pointer (gp)
x4:    thread pointer (tp)
x5:    link register (t0)
x8:    frame pointer (fp)
x10-x11:    arguments/return values (a0-1)
x12-x17:    arguments (a2-7)
x28-31:     temporaries (t3-6)
pc:    program counter (pc)

==> U-Boot will use gp to hold a pointer to the global data

Memory Management:

U-Boot runs in system state and uses physical addresses, i.e. the MMU is not used either for address mapping nor for memory protection.

The available memory is mapped to fixed addresses using the memory controller. In this process, a contiguous block is formed for each memory type (Flash, SDRAM, SRAM), even when it consists of several physical memory banks.

U-Boot is installed in the first 128 kB of the first Flash bank (on TQM8xxL modules this is the range 0x40000000 … 0x4001FFFF). After booting and sizing and initializing DRAM, the code relocates itself to the upper end of DRAM. Immediately below the U-Boot code some memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN configuration setting]. Below that, a structure with global Board Info data is placed, followed by the stack (growing downward).

Additionally, some exception handler code is copied to the low 8 kB of DRAM (0x00000000 … 0x00001FFF).

So a typical memory configuration with 16 MB of DRAM could look like this:

0x0000 0000    Exception Vector code
      :
0x0000 1FFF
0x0000 2000    Free for Application Use
      :
      :

      :
      :
0x00FB FF20    Monitor Stack (Growing downward)
0x00FB FFAC    Board Info Data and permanent copy of global data
0x00FC 0000    Malloc Arena
      :
0x00FD FFFF
0x00FE 0000    RAM Copy of Monitor Code
...        eventually: LCD or video framebuffer
...        eventually: pRAM (Protected RAM - unchanged by reset)
0x00FF FFFF    [End of RAM]

System Initialization:

In the reset configuration, U-Boot starts at the reset entry point (on most PowerPC systems at address 0x00000100). Because of the reset configuration for CS0# this is a mirror of the on board Flash memory. To be able to re-map memory U-Boot then jumps to its link address. To be able to implement the initialization code in C, a (small!) initial stack is set up in the internal Dual Ported RAM (in case CPUs which provide such a feature like), or in a locked part of the data cache. After that, U-Boot initializes the CPU core, the caches and the SIU.

Next, all (potentially) available memory banks are mapped using a preliminary mapping. For example, we put them on 512 MB boundaries (multiples of 0x20000000: SDRAM on 0x00000000 and 0x20000000, Flash on 0x40000000 and 0x60000000, SRAM on 0x80000000). Then UPM A is programmed for SDRAM access. Using the temporary configuration, a simple memory test is run that determines the size of the SDRAM banks.

When there is more than one SDRAM bank, and the banks are of different size, the largest is mapped first. For equal size, the first bank (CS2#) is mapped first. The first mapping is always for address 0x00000000, with any additional banks following immediately to create contiguous memory starting from 0.

Then, the monitor installs itself at the upper end of the SDRAM area and allocates memory for use by malloc() and for the global Board Info data; also, the exception vector code is copied to the low RAM pages, and the final stack is set up.

Only after this relocation will you have a “normal” C environment; until that you are restricted in several ways, mostly because you are running from ROM, and because the code will have to be relocated to a new address in RAM.

U-Boot Porting Guide:

[Based on messages by Jerry Van Baren in the U-Boot-Users mailing list, October 2002]

int main(int argc, char *argv[]) { sighandler_t no_more_time;

signal(SIGALRM, no_more_time);
alarm(PROJECT_DEADLINE - toSec (3 * WEEK));

if (available_money > available_manpower) {
    Pay consultant to port U-Boot;
    return 0;
}

Download latest U-Boot source;

Subscribe to u-boot mailing list;

if (clueless)
    email("Hi, I am new to U-Boot, how do I get started?");

while (learning) {
    Read the README file in the top level directory;
    Read https://www.denx.de/wiki/bin/view/DULG/Manual;
    Read applicable doc/README.*;
    Read the source, Luke;
    /* find . -name "*.[chS]" | xargs grep -i <keyword> */
}

if (available_money > toLocalCurrency ($2500))
    Buy a BDI3000;
else
    Add a lot of aggravation and time;

if (a similar board exists) {    /* hopefully... */
    cp -a board/<similar> board/<myboard>
    cp include/configs/<similar>.h include/configs/<myboard>.h
} else {
    Create your own board support subdirectory;
    Create your own board include/configs/<myboard>.h file;
}
Edit new board/<myboard> files
Edit new include/configs/<myboard>.h

while (!accepted) {
    while (!running) {
        do {
            Add / modify source code;
        } until (compiles);
        Debug;
        if (clueless)
            email("Hi, I am having problems...");
    }
    Send patch file to the U-Boot email list;
    if (reasonable critiques)
        Incorporate improvements from email list code review;
    else
        Defend code as written;
}

return 0;

}

void no_more_time (int sig) { hire_a_guru(); }

Coding Standards:

All contributions to U-Boot should conform to the Linux kernel coding style; see the kernel coding style guide at https://www.kernel.org/doc/html/latest/process/coding-style.html, and the script “scripts/Lindent” in your Linux kernel source directory.

Source files originating from a different project (for example the MTD subsystem) are generally exempt from these guidelines and are not reformatted to ease subsequent migration to newer versions of those sources.

Please note that U-Boot is implemented in C (and to some small parts in Assembler); no C++ is used, so please do not use C++ style comments (//) in your code.

Please also stick to the following formatting rules:

• remove any trailing white space
• use TAB characters for indentation and vertical alignment, not spaces
• make sure NOT to use DOS ‘\r\n’ line feeds
• do not add more than 2 consecutive empty lines to source files
• do not add trailing empty lines to source files

Submissions which do not conform to the standards may be returned with a request to reformat the changes.

Submitting Patches:

Since the number of patches for U-Boot is growing, we need to establish some rules. Submissions which do not conform to these rules may be rejected, even when they contain important and valuable stuff.

Please see https://www.denx.de/wiki/U-Boot/Patches for details.

Patches shall be sent to the u-boot mailing list u-boot@lists.denx.de; see https://lists.denx.de/listinfo/u-boot

When you send a patch, please include the following information with it:

• For bug fixes: a description of the bug and how your patch fixes this bug. Please try to include a way of demonstrating that the patch actually fixes something.

• For new features: a description of the feature and your implementation.

• For major contributions, add a MAINTAINERS file with your information and associated file and directory references.

• When you add support for a new board, don’t forget to add a maintainer e-mail address to the boards.cfg file, too.

• If your patch adds new configuration options, don’t forget to document these in the README file.

• The patch itself. If you are using git (which is strongly recommended) you can easily generate the patch using the “git format-patch”. If you then use “git send-email” to send it to the U-Boot mailing list, you will avoid most of the common problems with some other mail clients.

  If you cannot use git, use “diff -purN OLD NEW”. If your version of diff does not support these options, then get the latest version of GNU diff.

  The current directory when running this command shall be the parent directory of the U-Boot source tree (i. e. please make sure that your patch includes sufficient directory information for the affected files).

  We prefer patches as plain text. MIME attachments are discouraged, and compressed attachments must not be used.

• If one logical set of modifications affects or creates several files, all these changes shall be submitted in a SINGLE patch file.

• Changesets that contain different, unrelated modifications shall be submitted as SEPARATE patches, one patch per changeset.

Notes:

• Before sending the patch, run the buildman script on your patched source tree and make sure that no errors or warnings are reported for any of the boards.

• Keep your modifications to the necessary minimum: A patch containing several unrelated changes or arbitrary reformats will be returned with a request to re-formatting / split it.

• If you modify existing code, make sure that your new code does not add to the memory footprint of the code ;-) Small is beautiful! When adding new features, these should compile conditionally only (using #ifdef), and the resulting code with the new feature disabled must not need more memory than the old code without your modification.

• Remember that there is a size limit of 100 kB per message on the u-boot mailing list. Bigger patches will be moderated. If they are reasonable and not too big, they will be acknowledged. But patches bigger than the size limit should be avoided.