Booting U-boot on a MX28 processor
==================================

This document describes the MX28 U-Boot port. This document mostly
covers topics related to making the module/board bootable.

Terminology
-----------

The dollar symbol ($) introduces a snipped of shell code. This shall be typed
into the unix command prompt in U-Boot source code root directory.

The (=>) introduces a snipped of code that should by typed into U-Boot command
prompt

Contents
--------

1) Prerequisites
2) Compiling U-Boot for a MX28 based board
3) Installation of U-Boot for a MX28 based board to SD card

1) Prerequisites
----------------

To make a MX28 based board bootable, some tools are necessary. The first one
is the "elftosb" tool distributed by Freescale Semiconductor. The other one
is the "mxsboot" tool found in U-Boot source tree.

Firstly, obtain the elftosb archive from the following location:

	http://foss.doredevelopment.dk/mirrors/imx/elftosb-10.12.01.tar.gz

We use a $VER variable here to denote the current version. At the time of
writing of this document, that is "10.12.01". To obtain the file from command
line, use:

	$ VER="10.12.01"
	$ wget http://foss.doredevelopment.dk/mirrors/imx/elftosb-${VER}.tar.gz

Extract the file:

	$ tar xzf elftosb-${VER}.tar.gz

Compile the file. We need to manually tell the linker to use also libm:

	$ cd elftosb-${VER}/
	$ make LIBS="-lstdc++ -lm" elftosb

Optionally, remove debugging symbols from elftosb:

	$ strip bld/linux/elftosb

Finally, install the "elftosb" binary. The "install" target is missing, so just
copy the binary by hand:

	$ sudo cp bld/linux/elftosb /usr/local/bin/

Make sure the "elftosb" binary can be found in your $PATH, in this case this
means "/usr/local/bin/" has to be in your $PATH.

2) Compiling U-Boot for a MX28 based board
-------------------------------------------

Compiling the U-Boot for a MX28 board is straightforward and done as compiling U-Boot
for any other ARM device. For cross-compiler setup, please refer to ELDK5.0
documentation. First, clean up the source code:

	$ make mrproper

Next, configure U-Boot for a MX28 based board

	$ make <mx28_based_board_name>_config

Examples:

1. For building U-boot for Denx M28EVK board:

	$ make m28evk_config

2. For building U-boot for Freescale MX28EVK board:

	$ make mx28evk_config

Lastly, compile U-Boot and prepare a "BootStream". The "BootStream" is a special
type of file, which the i.MX28 CPU can boot. This is handled by the following
command:

	$ make u-boot.sb

HINT: To speed-up the build process, you can add -j<N>, where N is number of
      compiler instances that'll run in parallel.

The code produces "u-boot.sb" file. This file needs to be augmented with a
proper header to allow successful boot from SD or NAND. Adding the header is
discussed in the following chapters.

3) Installation of U-Boot for a MX28 based board to SD card
-----------------------------------------------------------

To boot a MX28 based board from SD, set the boot mode DIP switches according
to i.MX28 manual chapter 12.2.1 (Table 12-2), PORT=SSP0, SD/MMC master on
SSP0, 3.3V.


An SD card the i.MX28 CPU can use to boot U-Boot must contain a DOS partition
table, which in turn carries a partition of special type and which contains a
special header. The rest of partitions in the DOS partition table can be used
by the user.

To prepare such partition, use your favourite partitioning tool. The partition
must have the following parameters:

	* Start sector .......... sector 2048
	* Partition size ........ at least 1024 kb
	* Partition type ........ 0x53 (sometimes "OnTrack DM6 Aux3")

For example in Linux fdisk, the sequence for a clear card follows. Be sure to
run fdisk with the option "-u=sectors" to set units to sectors:

	* o ..................... create a clear partition table
	* n ..................... create new partition
		* p ............. primary partition
		* 1 ............. first partition
		* 2048 .......... first sector is 2048
		* +1M ........... make the partition 1Mb big
	* t 1 ................... change first partition ID
		* 53 ............ change the ID to 0x53 (OnTrack DM6 Aux3)
	* <create other partitions>
	* w ..................... write partition table to disk

The partition layout is ready, next the special partition must be filled with
proper contents. The contents is generated by running the following command
(see chapter 2)):

	$ ./tools/mxsboot sd u-boot.sb u-boot.sd

The resulting file, "u-boot.sd", shall then be written to the partition. In this
case, we assume the first partition of the SD card is /dev/mmcblk0p1:

	$ dd if=u-boot.sd of=/dev/mmcblk0p1

Last step is to insert the card into MX28 based board and boot.

NOTE: If the user needs to adjust the start sector, the "mxsboot" tool contains
      a "-p" switch for that purpose. The "-p" switch takes the sector number as
      an argument.

4) Installation of U-Boot for NAND flash
-----------------------------------------------

To boot a MX28 based board from NAND, set the boot mode DIP switches according to i.MX28
manual chapter 12.2.1 (Table 12-2), PORT=GPMI, NAND 1.8 V.

There are two possibilities when preparing an image writable to NAND flash.

	I) The NAND wasn't written at all yet or the BCB is broken
	----------------------------------------------------------
	   In this case, both BCB (FCB and DBBT) and firmware needs to be
	   written to NAND. To generate NAND image containing all these,
	   there is a tool called "mxsboot" in the "tools/" directory. The tool
	   is invoked on "u-boot.sb" file from chapter 2):

		 $ ./tools/mxsboot nand u-boot.sb u-boot.nand

	   NOTE: The above invokation works for NAND flash with geometry of
		 2048b per page, 64b OOB data, 128kb erase size. If your chip
		 has a different geometry, please use:

		 -w <size>	change page size (default 2048 b)
		 -o <size>	change oob size (default 64 b)
		 -e <size>	change erase size (default 131072 b)

		 The geometry information can be obtained from running U-Boot
		 on the MX28 board by issuing the "nand info" command.

	   The resulting file, "u-boot.nand" can be written directly to NAND
	   from the U-Boot prompt. To simplify the process, the U-Boot default
	   environment contains script "update_nand_full" to update the system.

	   This script expects a working TFTP server containing the file
	   "u-boot.nand" in it's root directory. This can be changed by
	   adjusting the "update_nand_full_filename" varible.

	   To update the system, run the following in U-Boot prompt:

		 => run update_nand_full

	   In case you would only need to update the bootloader in future,
	   see II) below.

	II) The NAND was already written with a good BCB
	------------------------------------------------
	   This part applies after the part I) above was done at least once.

	   If part I) above was done correctly already, there is no need to
	   write the FCB and DBBT parts of NAND again. It's possible to upgrade
	   only the bootloader image.

	   To simplify the process of firmware update, the U-Boot default
	   environment contains script "update_nand_firmware" to update only
	   the firmware, without rewriting FCB and DBBT.

	   This script expects a working TFTP server containing the file
	   "u-boot.sb" in it's root directory. This can be changed by
	   adjusting the "update_nand_firmware_filename" varible.

	   To update the system, run the following in U-Boot prompt:

		 => run update_nand_firmware

	III) Special settings for the update scripts
	--------------------------------------------
	   There is a slight possibility of the user wanting to adjust the
	   STRIDE and COUNT options of the NAND boot. For description of these,
	   see i.MX28 manual section 12.12.1.2 and 12.12.1.3.

	   The update scripts take this possibility into account. In case the
	   user changes STRIDE by blowing fuses, the user also has to change
	   "update_nand_stride" variable. In case the user changes COUNT by
	   blowing fuses, the user also has to change "update_nand_count"
	   variable for the update scripts to work correctly.

	   In case the user needs to boot a firmware image bigger than 1Mb, the
	   user has to adjust the "update_nand_firmware_maxsz" variable for the
	   update scripts to work properly.