Booting U-Boot on a MXS processor
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=================================
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This document describes the MXS U-Boot port. This document mostly covers topics
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related to making the module/board bootable.
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Terminology
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-----------
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The term "MXS" refers to a family of Freescale SoCs that is composed by MX23
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and MX28.
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The dollar symbol ($) introduces a snipped of shell code. This shall be typed
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into the unix command prompt in U-Boot source code root directory.
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The (=>) introduces a snipped of code that should by typed into U-Boot command
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prompt
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Contents
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--------
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1) Prerequisites
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2) Compiling U-Boot for a MXS based board
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3) Installation of U-Boot for a MXS based board to SD card
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4) Installation of U-Boot into NAND flash on a MX28 based board
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5) Installation of U-Boot into SPI NOR flash on a MX28 based board
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1) Prerequisites
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----------------
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To make a MXS based board bootable, some tools are necessary. The only
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mandatory tool is the "mxsboot" tool found in U-Boot source tree. The
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tool is built automatically when compiling U-Boot for i.MX23 or i.MX28.
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The production of BootStream image is handled via "mkimage", which is
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also part of the U-Boot source tree. The "mkimage" requires OpenSSL
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development libraries to be installed. In case of Debian and derivates,
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this is installed by running:
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$ sudo apt-get install libssl-dev
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NOTE: The "elftosb" tool distributed by Freescale Semiconductor is no
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longer necessary for general use of U-Boot on i.MX23 and i.MX28.
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The mkimage supports generation of BootStream images encrypted
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with a zero key, which is the vast majority of use-cases. In
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case you do need to produce image encrypted with non-zero key
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or other special features, please use the "elftosb" tool,
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otherwise continue to section 2). The installation procedure of
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the "elftosb" is outlined below:
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Firstly, obtain the elftosb archive from the following location:
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ftp://ftp.denx.de/pub/tools/elftosb-10.12.01.tar.gz
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We use a $VER variable here to denote the current version. At the time of
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writing of this document, that is "10.12.01". To obtain the file from command
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line, use:
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$ VER="10.12.01"
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$ wget ftp://ftp.denx.de/pub/tools/elftosb-${VER}.tar.gz
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Extract the file:
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$ tar xzf elftosb-${VER}.tar.gz
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Compile the file. We need to manually tell the linker to use also libm:
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$ cd elftosb-${VER}/
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$ make LIBS="-lstdc++ -lm" elftosb
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Optionally, remove debugging symbols from elftosb:
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$ strip bld/linux/elftosb
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Finally, install the "elftosb" binary. The "install" target is missing, so just
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copy the binary by hand:
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$ sudo cp bld/linux/elftosb /usr/local/bin/
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Make sure the "elftosb" binary can be found in your $PATH, in this case this
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means "/usr/local/bin/" has to be in your $PATH.
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2) Compiling U-Boot for a MXS based board
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-------------------------------------------
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Compiling the U-Boot for a MXS board is straightforward and done as compiling
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U-Boot for any other ARM device. For cross-compiler setup, please refer to
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ELDK5.0 documentation. First, clean up the source code:
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$ make mrproper
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Next, configure U-Boot for a MXS based board
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$ make <mxs_based_board_name>_config
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Examples:
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1. For building U-Boot for Aries M28EVK board:
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$ make m28evk_config
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2. For building U-Boot for Freescale MX28EVK board:
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$ make mx28evk_config
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3. For building U-Boot for Freescale MX23EVK board:
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$ make mx23evk_config
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4. For building U-Boot for Olimex MX23 Olinuxino board:
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$ make mx23_olinuxino_config
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Lastly, compile U-Boot and prepare a "BootStream". The "BootStream" is a special
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type of file, which MXS CPUs can boot. This is handled by the following
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command:
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$ make u-boot.sb
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HINT: To speed-up the build process, you can add -j<N>, where N is number of
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compiler instances that'll run in parallel.
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The code produces "u-boot.sb" file. This file needs to be augmented with a
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proper header to allow successful boot from SD or NAND. Adding the header is
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discussed in the following chapters.
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NOTE: The process that produces u-boot.sb uses the mkimage to generate the
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BootStream. The BootStream is encrypted with zero key. In case you need
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some special features of the BootStream and plan on using the "elftosb"
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tool instead, the invocation to produce a compatible BootStream with the
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one produced by mkimage is outlined below. For further details, refer to
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the documentation bundled with the "elftosb" package.
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$ elftosb -zf imx23 -c arch/arm/cpu/arm926ejs/mxs/u-boot-imx23.bd \
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-o u-boot.sb
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$ elftosb -zf imx28 -c arch/arm/cpu/arm926ejs/mxs/u-boot-imx28.bd \
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-o u-boot.sb
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3) Installation of U-Boot for a MXS based board to SD card
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----------------------------------------------------------
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To boot a MXS based board from SD, set the boot mode DIP switches according to
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to MX28 manual, section 12.2.1 (Table 12-2) or MX23 manual, section 35.1.2
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(Table 35-3).
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The SD card used to boot U-Boot must contain a DOS partition table, which in
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turn carries a partition of special type and which contains a special header.
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The rest of partitions in the DOS partition table can be used by the user.
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To prepare such partition, use your favourite partitioning tool. The partition
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must have the following parameters:
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* Start sector .......... sector 2048
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* Partition size ........ at least 1024 kb
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* Partition type ........ 0x53 (sometimes "OnTrack DM6 Aux3")
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For example in Linux fdisk, the sequence for a clear card follows. Be sure to
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run fdisk with the option "-u=sectors" to set units to sectors:
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* o ..................... create a clear partition table
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* n ..................... create new partition
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* p ............. primary partition
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* 1 ............. first partition
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* 2048 .......... first sector is 2048
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* +1M ........... make the partition 1Mb big
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* t 1 ................... change first partition ID
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* 53 ............ change the ID to 0x53 (OnTrack DM6 Aux3)
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* <create other partitions>
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* w ..................... write partition table to disk
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The partition layout is ready, next the special partition must be filled with
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proper contents. The contents is generated by running the following command
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(see chapter 2)):
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$ ./tools/mxsboot sd u-boot.sb u-boot.sd
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The resulting file, "u-boot.sd", shall then be written to the partition. In this
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case, we assume the first partition of the SD card is /dev/mmcblk0p1:
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$ dd if=u-boot.sd of=/dev/mmcblk0p1
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Last step is to insert the card into the MXS based board and boot.
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NOTE: If the user needs to adjust the start sector, the "mxsboot" tool contains
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a "-p" switch for that purpose. The "-p" switch takes the sector number as
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an argument.
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4) Installation of U-Boot into NAND flash on a MX28 based board
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---------------------------------------------------------------
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To boot a MX28 based board from NAND, set the boot mode DIP switches according
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to MX28 manual section 12.2.1 (Table 12-2), PORT=GPMI, NAND 1.8 V.
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There are two possibilities when preparing an image writable to NAND flash.
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I) The NAND wasn't written at all yet or the BCB is broken
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----------------------------------------------------------
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In this case, both BCB (FCB and DBBT) and firmware needs to be
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written to NAND. To generate NAND image containing all these,
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there is a tool called "mxsboot" in the "tools/" directory. The tool
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is invoked on "u-boot.sb" file from chapter 2):
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$ ./tools/mxsboot nand u-boot.sb u-boot.nand
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NOTE: The above invokation works for NAND flash with geometry of
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2048b per page, 64b OOB data, 128kb erase size. If your chip
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has a different geometry, please use:
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-w <size> change page size (default 2048 b)
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-o <size> change oob size (default 64 b)
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-e <size> change erase size (default 131072 b)
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The geometry information can be obtained from running U-Boot
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on the MX28 board by issuing the "nand info" command.
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The resulting file, "u-boot.nand" can be written directly to NAND
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from the U-Boot prompt. To simplify the process, the U-Boot default
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environment contains script "update_nand_full" to update the system.
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This script expects a working TFTP server containing the file
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"u-boot.nand" in it's root directory. This can be changed by
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adjusting the "update_nand_full_filename" variable.
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To update the system, run the following in U-Boot prompt:
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=> run update_nand_full
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In case you would only need to update the bootloader in future,
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see II) below.
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II) The NAND was already written with a good BCB
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------------------------------------------------
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This part applies after the part I) above was done at least once.
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If part I) above was done correctly already, there is no need to
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write the FCB and DBBT parts of NAND again. It's possible to upgrade
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only the bootloader image.
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To simplify the process of firmware update, the U-Boot default
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environment contains script "update_nand_firmware" to update only
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the firmware, without rewriting FCB and DBBT.
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This script expects a working TFTP server containing the file
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"u-boot.sb" in it's root directory. This can be changed by
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adjusting the "update_nand_firmware_filename" variable.
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To update the system, run the following in U-Boot prompt:
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=> run update_nand_firmware
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III) Special settings for the update scripts
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--------------------------------------------
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There is a slight possibility of the user wanting to adjust the
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STRIDE and COUNT options of the NAND boot. For description of these,
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see MX28 manual section 12.12.1.2 and 12.12.1.3.
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The update scripts take this possibility into account. In case the
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user changes STRIDE by blowing fuses, the user also has to change
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"update_nand_stride" variable. In case the user changes COUNT by
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blowing fuses, the user also has to change "update_nand_count"
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variable for the update scripts to work correctly.
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In case the user needs to boot a firmware image bigger than 1Mb, the
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user has to adjust the "update_nand_firmware_maxsz" variable for the
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update scripts to work properly.
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5) Installation of U-Boot into SPI NOR flash on a MX28 based board
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------------------------------------------------------------------
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The u-boot.sb file can be directly written to SPI NOR from U-Boot prompt.
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Load u-boot.sb into RAM, this can be done in several ways and one way is to use
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tftp:
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=> tftp u-boot.sb 0x42000000
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Probe the SPI NOR flash:
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=> sf probe
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(SPI NOR should be succesfully detected in this step)
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Erase the blocks where U-Boot binary will be written to:
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=> sf erase 0x0 0x80000
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Write u-boot.sb to SPI NOR:
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=> sf write 0x42000000 0 0x80000
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Power off the board and set the boot mode DIP switches to boot from the SPI NOR
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according to MX28 manual section 12.2.1 (Table 12-2)
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Last step is to power up the board and U-Boot should start from SPI NOR.
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