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(C) Copyright 2000 - 2013

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

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SPDX-License-Identifier: GPL-2.0+

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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 and CREDITS files to find out who contributed the specific port. The boards.cfg file lists board maintainers.

Note: There is no CHANGELOG file in the actual U-Boot source tree; 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 http://lists.denx.de/pipermail/u-boot and http://dir.gmane.org/gmane.comp.boot-loaders.u-boot

Where to get source code:

The U-Boot source code is maintained in the git repository at git://www.denx.de/git/u-boot.git ; you can browse it online at http://www.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=summary

The "snapshot" links on this page allow you to download tarballs of any version you might be interested in. Official releases are also available for FTP download from the ftp://ftp.denx.de/pub/u-boot/ directory.

Pre-built (and tested) images are available from ftp://ftp.denx.de/pub/u-boot/images/

Where we come from:

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 "uboot" or on "UBOOT". 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 candiate 1 for September 2010 release

Directory Hierarchy:

/arch Architecture specific files /arc Files generic to ARC architecture /cpu CPU specific files /arc700 Files specific to ARC 700 CPUs /lib Architecture specific library files /arm Files generic to ARM architecture /cpu CPU specific files /arm720t Files specific to ARM 720 CPUs /arm920t Files specific to ARM 920 CPUs /at91 Files specific to Atmel AT91RM9200 CPU /imx Files specific to Freescale MC9328 i.MX CPUs /s3c24x0 Files specific to Samsung S3C24X0 CPUs /arm926ejs Files specific to ARM 926 CPUs /arm1136 Files specific to ARM 1136 CPUs /pxa Files specific to Intel XScale PXA CPUs /sa1100 Files specific to Intel StrongARM SA1100 CPUs /lib Architecture specific library files /avr32 Files generic to AVR32 architecture /cpu CPU specific files /lib Architecture specific library files /blackfin Files generic to Analog Devices Blackfin architecture /cpu CPU specific files /lib Architecture specific library files /m68k Files generic to m68k architecture /cpu CPU specific files /mcf52x2 Files specific to Freescale ColdFire MCF52x2 CPUs /mcf5227x Files specific to Freescale ColdFire MCF5227x CPUs /mcf532x Files specific to Freescale ColdFire MCF5329 CPUs /mcf5445x Files specific to Freescale ColdFire MCF5445x CPUs /mcf547x8x Files specific to Freescale ColdFire MCF547x8x CPUs /lib Architecture specific library files /microblaze Files generic to microblaze architecture /cpu CPU specific files /lib Architecture specific library files /mips Files generic to MIPS architecture /cpu CPU specific files /mips32 Files specific to MIPS32 CPUs /mips64 Files specific to MIPS64 CPUs /lib Architecture specific library files /nds32 Files generic to NDS32 architecture /cpu CPU specific files /n1213 Files specific to Andes Technology N1213 CPUs /lib Architecture specific library files /nios2 Files generic to Altera NIOS2 architecture /cpu CPU specific files /lib Architecture specific library files /openrisc Files generic to OpenRISC architecture /cpu CPU specific files /lib Architecture specific library files /powerpc Files generic to PowerPC architecture /cpu CPU specific files /mpc5xx Files specific to Freescale MPC5xx CPUs /mpc5xxx Files specific to Freescale MPC5xxx CPUs /mpc8xx Files specific to Freescale MPC8xx CPUs /mpc8260 Files specific to Freescale MPC8260 CPUs /mpc85xx Files specific to Freescale MPC85xx CPUs /ppc4xx Files specific to AMCC PowerPC 4xx CPUs /lib Architecture specific library files /sh Files generic to SH architecture /cpu CPU specific files /sh2 Files specific to sh2 CPUs /sh3 Files specific to sh3 CPUs /sh4 Files specific to sh4 CPUs /lib Architecture specific library files /sparc Files generic to SPARC architecture /cpu CPU specific files /leon2 Files specific to Gaisler LEON2 SPARC CPU /leon3 Files specific to Gaisler LEON3 SPARC CPU /lib Architecture specific library files /x86 Files generic to x86 architecture /cpu CPU specific files /lib Architecture specific library files /api Machine/arch independent API for external apps /board Board dependent files /common Misc architecture independent functions /disk Code for disk drive partition handling /doc Documentation (don't expect too much) /drivers Commonly used device drivers /dts Contains Makefile for building internal U-Boot fdt. /examples Example code for standalone applications, etc. /fs Filesystem code (cramfs, ext2, jffs2, etc.) /include Header Files /lib Files generic to all architectures /libfdt Library files to support flattened device trees /lzma Library files to support LZMA decompression /lzo Library files to support LZO decompression /net Networking code /post Power On Self Test /spl Secondary Program Loader framework /tools Tools to build S-Record or U-Boot images, etc.

Software Configuration:

Configuration is usually done using C preprocessor defines; the rationale behind that is to avoid dead code whenever possible.

There are two classes of configuration variables:

Later we will add a configuration tool - probably similar to or even identical to what's used for the Linux kernel. Right now, we have to do the configuration by hand, which means creating some symbolic links and editing some configuration files. We use the TQM8xxL boards as an example here.

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

For the Cogent platform, you need to specify the CPU type as well; e.g. "make cogentmpc8xxdefconfig". And also configure the cogent directory according to the instructions in cogent/README.

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 board/sandbox/README.sandbox 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). At present SPL mostly uses a separate code path, but the funtion 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 CONFIGSPLFRAMEWORK conform to this.

Execution starts with start.S with three functions called during init after that. The purpose and limitations of each is described below.

lowlevelinit(): - purpose: essential init to permit execution to reach boardinitf() - no globaldata 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 boardinitf() - this is almost never needed - return normally from this function

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

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
- these is no need to clear BSS, it will be done by crt0.S
- must return normally from this function (don't call board_init_r()
    directly)

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

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

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_SPL_STACK_R_ADDR points into SDRAM
- preloader_console_init() can be called here - typically this is
    done by defining CONFIG_SPL_BOARD_INIT and then supplying a
    spl_board_init() function containing this call
- loads U-Boot or (in falcon mode) Linux

Configuration Options:

Configuration depends on the combination of board and CPU type; all such information is kept in a configuration file "include/configs/.h".

Example: For a TQM823L module, all configuration settings are in "include/configs/TQM823L.h".

Many of the options are named exactly as the corresponding Linux kernel configuration options. The intention is to make it easier to build a config tool - later.

The following options need to be configured:

CBFS (Coreboot Filesystem) support CONFIGCMDCBFS

    Define this to enable support for reading from a Coreboot
    filesystem. Available commands are cbfsinit, cbfsinfo, cbfsls
    and cbfsload.

Legacy uImage format:

Arg Where When 1 common/cmdbootm.c before attempting to boot an image -1 common/cmdbootm.c Image header has bad magic number 2 common/cmdbootm.c Image header has correct magic number -2 common/cmdbootm.c Image header has bad checksum 3 common/cmdbootm.c Image header has correct checksum -3 common/cmdbootm.c Image data has bad checksum 4 common/cmdbootm.c Image data has correct checksum -4 common/cmdbootm.c Image is for unsupported architecture 5 common/cmdbootm.c Architecture check OK -5 common/cmdbootm.c Wrong Image Type (not kernel, multi) 6 common/cmdbootm.c Image Type check OK -6 common/cmdbootm.c gunzip uncompression error -7 common/cmdbootm.c Unimplemented compression type 7 common/cmdbootm.c Uncompression OK 8 common/cmdbootm.c No uncompress/copy overwrite error -9 common/cmdbootm.c Unsupported OS (not Linux, BSD, VxWorks, QNX)

9   common/image.c      Start initial ramdisk verification

-10 common/image.c Ramdisk header has bad magic number -11 common/image.c Ramdisk header has bad checksum 10 common/image.c Ramdisk header is OK -12 common/image.c Ramdisk data has bad checksum 11 common/image.c Ramdisk data has correct checksum 12 common/image.c Ramdisk verification complete, start loading -13 common/image.c Wrong Image Type (not PPC Linux ramdisk) 13 common/image.c Start multifile image verification 14 common/image.c No initial ramdisk, no multifile, continue.

15 arch//lib/bootm.c All preparation done, transferring control to OS

-30 arch/powerpc/lib/board.c Fatal error, hang the system -31 post/post.c POST test failed, detected by postoutputbacklog() -32 post/post.c POST test failed, detected by postrunsingle()

34 common/cmddoc.c before loading a Image from a DOC device -35 common/cmddoc.c Bad usage of "doc" command 35 common/cmddoc.c correct usage of "doc" command -36 common/cmddoc.c No boot device 36 common/cmddoc.c correct boot device -37 common/cmddoc.c Unknown Chip ID on boot device 37 common/cmddoc.c correct chip ID found, device available -38 common/cmddoc.c Read Error on boot device 38 common/cmddoc.c reading Image header from DOC device OK -39 common/cmddoc.c Image header has bad magic number 39 common/cmddoc.c Image header has correct magic number -40 common/cmddoc.c Error reading Image from DOC device 40 common/cmddoc.c Image header has correct magic number 41 common/cmdide.c before loading a Image from a IDE device -42 common/cmdide.c Bad usage of "ide" command 42 common/cmdide.c correct usage of "ide" command -43 common/cmdide.c No boot device 43 common/cmdide.c boot device found -44 common/cmdide.c Device not available 44 common/cmdide.c Device available -45 common/cmdide.c wrong partition selected 45 common/cmdide.c partition selected -46 common/cmdide.c Unknown partition table 46 common/cmdide.c valid partition table found -47 common/cmdide.c Invalid partition type 47 common/cmdide.c correct partition type -48 common/cmdide.c Error reading Image Header on boot device 48 common/cmdide.c reading Image Header from IDE device OK -49 common/cmdide.c Image header has bad magic number 49 common/cmdide.c Image header has correct magic number -50 common/cmdide.c Image header has bad checksum 50 common/cmdide.c Image header has correct checksum -51 common/cmdide.c Error reading Image from IDE device 51 common/cmdide.c reading Image from IDE device OK 52 common/cmdnand.c before loading a Image from a NAND device -53 common/cmdnand.c Bad usage of "nand" command 53 common/cmdnand.c correct usage of "nand" command -54 common/cmdnand.c No boot device 54 common/cmdnand.c boot device found -55 common/cmdnand.c Unknown Chip ID on boot device 55 common/cmdnand.c correct chip ID found, device available -56 common/cmdnand.c Error reading Image Header on boot device 56 common/cmdnand.c reading Image Header from NAND device OK -57 common/cmdnand.c Image header has bad magic number 57 common/cmdnand.c Image header has correct magic number -58 common/cmdnand.c Error reading Image from NAND device 58 common/cmd_nand.c reading Image from NAND device OK

-60 common/env_common.c Environment has a bad CRC, using default

64 net/eth.c starting with Ethernet configuration. -64 net/eth.c no Ethernet found. 65 net/eth.c Ethernet found.

-80 common/cmdnet.c usage wrong 80 common/cmdnet.c before calling netloop() -81 common/cmdnet.c some error in netloop() occurred 81 common/cmdnet.c netloop() back without error -82 common/cmdnet.c size == 0 (File with size 0 loaded) 82 common/cmdnet.c trying automatic boot 83 common/cmdnet.c running "source" command -83 common/cmdnet.c some error in automatic boot or "source" command 84 common/cmdnet.c end without errors

FIT uImage format:

Arg Where When 100 common/cmdbootm.c Kernel FIT Image has correct format -100 common/cmdbootm.c Kernel FIT Image has incorrect format 101 common/cmdbootm.c No Kernel subimage unit name, using configuration -101 common/cmdbootm.c Can't get configuration for kernel subimage 102 common/cmdbootm.c Kernel unit name specified -103 common/cmdbootm.c Can't get kernel subimage node offset 103 common/cmdbootm.c Found configuration node 104 common/cmdbootm.c Got kernel subimage node offset -104 common/cmdbootm.c Kernel subimage hash verification failed 105 common/cmdbootm.c Kernel subimage hash verification OK -105 common/cmdbootm.c Kernel subimage is for unsupported architecture 106 common/cmdbootm.c Architecture check OK -106 common/cmdbootm.c Kernel subimage has wrong type 107 common/cmdbootm.c Kernel subimage type OK -107 common/cmdbootm.c Can't get kernel subimage data/size 108 common/cmdbootm.c Got kernel subimage data/size -108 common/cmdbootm.c Wrong image type (not legacy, FIT) -109 common/cmdbootm.c Can't get kernel subimage type -110 common/cmdbootm.c Can't get kernel subimage comp -111 common/cmdbootm.c Can't get kernel subimage os -112 common/cmdbootm.c Can't get kernel subimage load address -113 common/cmdbootm.c Image uncompress/copy overwrite error

120 common/image.c Start initial ramdisk verification -120 common/image.c Ramdisk FIT image has incorrect format 121 common/image.c Ramdisk FIT image has correct format 122 common/image.c No ramdisk subimage unit name, using configuration -122 common/image.c Can't get configuration for ramdisk subimage 123 common/image.c Ramdisk unit name specified -124 common/image.c Can't get ramdisk subimage node offset 125 common/image.c Got ramdisk subimage node offset -125 common/image.c Ramdisk subimage hash verification failed 126 common/image.c Ramdisk subimage hash verification OK -126 common/image.c Ramdisk subimage for unsupported architecture 127 common/image.c Architecture check OK -127 common/image.c Can't get ramdisk subimage data/size 128 common/image.c Got ramdisk subimage data/size 129 common/image.c Can't get ramdisk load address -129 common/image.c Got ramdisk load address

-130 common/cmddoc.c Incorrect FIT image format 131 common/cmddoc.c FIT image format OK

-140 common/cmdide.c Incorrect FIT image format 141 common/cmdide.c FIT image format OK

-150 common/cmdnand.c Incorrect FIT image format 151 common/cmdnand.c FIT image format OK

Modem Support:

[so far only for SMDK2400 boards]

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/yourarchitecture/lib/board.c typically in boardinitf() and boardinit_r().

Configuration Settings:

The following definitions that deal with the placement and management of environment data (variable area); in general, we support the following configurations: 08a8a1ac14812b9fb3c0bb33b02eb505

b) Sometimes flash chips have few, equal sized, BIG sectors. In such a case you don't want to spend a whole sector for the environment.

BE CAREFUL! Any changes to the flash layout, and some changes to the source code will make it necessary to adapt /u-boot.lds* accordingly!

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.

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 getenv_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.

Low Level (hardware related) configuration options:

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.

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.

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 http://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

Note: If you wish to generate Windows versions of the utilities in the tools directory you can use the MinGW toolchain (http://www.mingw.org). Set your HOST tools to the MinGW toolchain and execute 'make tools'. For example:

   $ make HOSTCC=i586-mingw32msvc-gcc HOSTSTRIP=i586-mingw32msvc-strip tools

  Binaries such as tools/mkimage.exe will be created which can
  be executed on computers running Windows.

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 boards.cfg for supported names.

Note: for some board 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:

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 KBUILDOUTPUT=/tmp/build make distclean make NAMEdefconfig make all

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

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. Add a new configuration option for your board to the toplevel "boards.cfg" file, using the existing entries as examples. Follow the instructions there to keep the boards in order.
  2. 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", a ".c", "flash.c" and "u-boot.lds".
  3. Create a new configuration file "include/configs/.h" for your board
  4. 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.
  5. Run "make _defconfig" with your new name.
  6. Type "make", and you should get a working "u-boot.srec" file to be installed on your target system.
  7. 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 "MAKEALL" script, which will configure and build U-Boot for ALL supported system. Be warned, this will take a while. You can select which (cross) compiler to use by passing a `CROSS_COMPILE' environment variable to the script, i. e. to use the ELDK cross tools you can type

CROSS_COMPILE=ppc_8xx- MAKEALL

or to build on a native PowerPC system you can type

CROSS_COMPILE=' ' MAKEALL

When using the MAKEALL script, the default behaviour is to build U-Boot in the source directory. This location can be changed by setting the BUILDDIR environment variable. Also, for each target built, the MAKEALL script saves two log files (.ERR and .MAKEALL) in the /LOG directory. This default location can be changed by setting the MAKEALLLOGDIR environment variable. For example:

export BUILD_DIR=/tmp/build
export MAKEALL_LOGDIR=/tmp/log
CROSS_COMPILE=ppc_8xx- MAKEALL

With the above settings build objects are saved in the /tmp/build, log files are saved in the /tmp/log and the source tree remains clean during the whole build process.

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) md - memory display mm - memory modify (auto-incrementing) nm - memory modify (constant address) mw - memory write (fill) 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 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 ".

Environment Variables:

U-Boot supports user configuration using Environment Variables which can be made persistent by saving to Flash memory.

Environment Variables are set using "setenv", printed using "printenv", and saved to Flash using "saveenv". Using "setenv" without a value can be used to delete a variable from the environment. As long as you don't save the environment you are working with an in-memory copy. In case the Flash area containing the environment is erased by accident, a default environment is provided.

Some configuration options can be set using Environment Variables.

List of environment variables (most likely not complete):

baudrate - see CONFIG_BAUDRATE

bootdelay - see CONFIG_BOOTDELAY

bootcmd - see CONFIG_BOOTCOMMAND

bootargs - Boot arguments when booting an RTOS image

bootfile - Name of the image to load with TFTP

bootmlow - Memory range available for image processing in the bootm command can be restricted. This variable is given as a hexadecimal number and defines lowest address allowed for use by the bootm command. See also "bootmsize" environment variable. Address defined by "bootmlow" is also the base of the initial memory mapping for the Linux kernel -- see the description of CONFIGSYSBOOTMAPSZ and bootmmapsize.

bootmmapsize - Size of the initial memory mapping for the Linux kernel. This variable is given as a hexadecimal number and it defines the size of the memory region starting at base address bootmlow that is accessible by the Linux kernel during early boot. If unset, CONFIGSYSBOOTMAPSZ is used as the default value if it is defined, and bootm_size is used otherwise.

bootmsize - Memory range available for image processing in the bootm command can be restricted. This variable is given as a hexadecimal number and defines the size of the region allowed for use by the bootm command. See also "bootmlow" environment variable.

updatefile - Location of the software update file on a TFTP server, used by the automatic software update feature. Please refer to documentation in doc/README.update for more details.

autoload - if set to "no" (any string beginning with 'n'), "bootp" will just load perform a lookup of the configuration from the BOOTP server, but not try to load any image using TFTP

autostart - if set to "yes", an image loaded using the "bootp", "rarpboot", "tftpboot" or "diskboot" commands will be automatically started (by internally calling "bootm")

      If set to "no", a standalone image passed to the
      "bootm" command will be copied to the load address
      (and eventually uncompressed), but NOT be started.
      This can be used to load and uncompress arbitrary
      data.

fdthigh - if set this restricts the maximum address that the flattened device tree will be copied into upon boot. For example, if you have a system with 1 GB memory at physical address 0x10000000, while Linux kernel only recognizes the first 704 MB as low memory, you may need to set fdthigh as 0x3C000000 to have the device tree blob be copied to the maximum address of the 704 MB low memory, so that Linux kernel can access it during the boot procedure.

      If this is set to the special value 0xFFFFFFFF then
      the fdt will not be copied at all on boot.  For this
      to work it must reside in writable memory, have
      sufficient padding on the end of it for u-boot to
      add the information it needs into it, and the memory
      must be accessible by the kernel.

fdtcontroladdr- if set this is the address of the control flattened device tree used by U-Boot when CONFIGOFCONTROL is defined.

i2cfast - (PPC405GP|PPC405EP only) if set to 'y' configures Linux I2C driver for fast mode (400kHZ). This environment variable is used in initialization code. So, for changes to be effective it must be saved and board must be reset.

initrdhigh - restrict positioning of initrd images: If this variable is not set, initrd images will be copied to the highest possible address in RAM; this is usually what you want since it allows for maximum initrd size. If for some reason you want to make sure that the initrd image is loaded below the CONFIGSYS_BOOTMAPSZ limit, you can set this environment variable to a value of "no" or "off" or "0". Alternatively, you can set it to a maximum upper address to use (U-Boot will still check that it does not overwrite the U-Boot stack and data).

      For instance, when you have a system with 16 MB
      RAM, and want to reserve 4 MB from use by Linux,
      you can do this by adding "mem=12M" to the value of
      the "bootargs" variable. However, now you must make
      sure that the initrd image is placed in the first
      12 MB as well - this can be done with

      setenv initrd_high 00c00000

      If you set initrd_high to 0xFFFFFFFF, this is an
      indication to U-Boot that all addresses are legal
      for the Linux kernel, including addresses in flash
      memory. In this case U-Boot will NOT COPY the
      ramdisk at all. This may be useful to reduce the
      boot time on your system, but requires that this
      feature is supported by your Linux kernel.

ipaddr - IP address; needed for tftpboot command

loadaddr - Default load address for commands like "bootp", "rarpboot", "tftpboot", "loadb" or "diskboot"

loadsecho - see CONFIGLOADS_ECHO

serverip - TFTP server IP address; needed for tftpboot command

bootretry - see CONFIGBOOTRETRY_TIME

bootdelaykey - see CONFIGAUTOBOOTDELAY_STR

bootstopkey - see CONFIGAUTOBOOTSTOP_STR

ethprime - controls which interface is used first.

ethact - controls which interface is currently active. For example you can do the following

      => setenv ethact FEC
      => ping 192.168.0.1 # traffic sent on FEC
      => setenv ethact SCC
      => ping 10.0.0.1 # traffic sent on SCC

ethrotate - When set to "no" U-Boot does not go through all available network interfaces. It just stays at the currently selected interface.

netretry - When set to "no" each network operation will either succeed or fail without retrying. When set to "once" the network operation will fail when all the available network interfaces are tried once without success. Useful on scripts which control the retry operation themselves.

npe_ucode - set load address for the NPE microcode

silent_linux - If set then Linux will be told to boot silently, by changing the console to be empty. If "yes" it will be made silent. If "no" it will not be made silent. If unset, then it will be made silent if the U-Boot console is silent.

tftpsrcport - If this is set, the value is used for TFTP's UDP source port.

tftpdstport - If this is set, the value is used for TFTP's UDP destination port instead of the Well Know Port 69.

tftpblocksize - Block size to use for TFTP transfers; if not set, we use the TFTP server's default block size

tftptimeout - Retransmission timeout for TFTP packets (in milli- seconds, minimum value is 1000 = 1 second). Defines when a packet is considered to be lost so it has to be retransmitted. The default is 5000 = 5 seconds. Lowering this value may make downloads succeed faster in networks with high packet loss rates or with unreliable TFTP servers.

vlan - When set to a value < 4095 the traffic over Ethernet is encapsulated/received over 802.1q VLAN tagged frames.

The following image location variables contain the location of images used in booting. The "Image" column gives the role of the image and is not an environment variable name. The other columns are environment variable names. "File Name" gives the name of the file on a TFTP server, "RAM Address" gives the location in RAM the image will be loaded to, and "Flash Location" gives the image's address in NOR flash or offset in NAND flash.

Note - these variables don't have to be defined for all boards, some boards currently use other variables for these purposes, and some boards use these variables for other purposes.

Image File Name RAM Address Flash Location ----- --------- ----------- -------------- u-boot u-boot u-bootaddrr u-bootaddr Linux kernel bootfile kerneladdrr kerneladdr device tree blob fdtfile fdtaddrr fdtaddr ramdisk ramdiskfile ramdiskaddrr ramdiskaddr

The following environment variables may be used and automatically updated by the network boot commands ("bootp" and "rarpboot"), depending the information provided by your boot server:

bootfile - see above dnsip - IP address of your Domain Name Server dnsip2 - IP address of your secondary Domain Name Server gatewayip - IP address of the Gateway (Router) to use hostname - Target hostname ipaddr - see above netmask - Subnet Mask rootpath - Pathname of the root filesystem on the NFS server serverip - see above

There are two special Environment Variables:

serial# - contains hardware identification information such as type string and/or serial number ethaddr - Ethernet address

These variables can be set only once (usually during manufacturing of the board). U-Boot refuses to delete or overwrite these variables once they have been set once.

Further special Environment Variables:

ver - Contains the U-Boot version string as printed with the "version" command. This variable is readonly (see CONFIGVERSIONVARIABLE).

Please note that changes to some configuration parameters may take only effect after the next boot (yes, that's just like Windoze :-).

Callback functions for environment variables:

For some environment variables, the behavior of u-boot needs to change when their values are changed. This functionality allows functions to be associated with arbitrary variables. On creation, overwrite, or deletion, the callback will provide the opportunity for some side effect to happen or for the change to be rejected.

The callbacks are named and associated with a function using the UBOOTENV_CALLBACK macro in your board or driver code.

These callbacks are associated with variables in one of two ways. The static list can be added to by defining CONFIGENVCALLBACKLISTSTATIC in the board configuration to a string that defines a list of associations. The list must be in the following format:

entry = variable_name[:callback_name]
list = entry[,list]

If the callback name is not specified, then the callback is deleted. Spaces are also allowed anywhere in the list.

Callbacks can also be associated by defining the ".callbacks" variable with the same list format above. Any association in ".callbacks" will override any association in the static list. You can define CONFIGENVCALLBACKLISTDEFAULT to a list (string) to define the ".callbacks" environment variable in the default or embedded environment.

If CONFIGREGEX is defined, the variablename above is evaluated as a regular expression. This allows multiple variables to be connected to the same callback without explicitly listing them all out.

Command Line Parsing:

There are two different command line parsers available with U-Boot: the old "simple" one, and the much more powerful "hush" shell:

Old, simple command line parser:

Hush shell:

General rules:

(1) If a command line (or an environment variable executed by a "run" command) contains several commands separated by semicolon, and one of these commands fails, then the remaining commands will be executed anyway.

(2) If you execute several variables with one call to run (i. e. calling run with a list of variables as arguments), any failing command will cause "run" to terminate, i. e. the remaining variables are not executed.

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 CONFIGNETRANDOM_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:

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:

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 IMAPADDR uses the same value as your U-Boot configuration in CONFIGSYS_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:

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:

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" is a tool to disassemble images built by mkimage. Its "-i" option performs the converse operation of the mkimage's second form (the "-d" option). Given an image built by mkimage, the dumpimage extracts a "data file" from the image:

tools/dumpimage -i image -T type -p position data_file
  -i ==> extract from the 'image' a specific 'data_file'
  -T ==> set image type to 'type'
  -p ==> 'position' (starting at 0) of the 'data_file' inside the 'image'

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 CONFIGSUPPORTRAW_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 http://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 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-bootstage2/); in the meantime, see ftp://ftp.denx.de/pub/u-boot/ppcbootstage2.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:

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 (gdt) 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 Blackfin, the normal C ABI (except for P3) is followed as documented here: http://docs.blackfin.uclinux.org/doku.php?id=applicationbinaryinterface

==> U-Boot will use P3 to hold a pointer to the global 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: http://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 NDS32, the following registers are used:

R0-R1:  argument/return
R2-R5:  argument
R15:    temporary register for assembler
R16:    trampoline register
R28:    frame pointer (FP)
R29:    global pointer (GP)
R30:    link register (LP)
R31:    stack pointer (SP)
PC: program counter (PC)

==> U-Boot will use R10 to hold a pointer to the global data

NOTE: DECLAREGLOBALDATA_PTR must be used with file-global scope, or current versions of GCC may "optimize" the code too much.

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 CONFIGSYSMALLOC_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 MPC8xx or MPC8260), 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[]) { sighandlert nomore_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 http://www.denx.de/twiki/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 nomoretime (int sig) { hireaguru(); }

Coding Standards:

All contributions to U-Boot should conform to the Linux kernel coding style; see the file "Documentation/CodingStyle" 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 http://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 http://lists.denx.de/mailman/listinfo/u-boot

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

Notes: