DESK-MX6UL-L/Development/How to create a bootable microSD card

History
Version	Issue Date	Notes
1.0.1	Jun 2021	First DESK release

How to create a bootable SD card

The procedure described here was tested with a physical machine. In case of a virtual machine such as the MVM, it might not work properly. Also, it is worth remembering that USB controller of the MVM is disabled by default. See also this section.

This article shows how to create a bootable microSD for the [[DESK-MX6UL-L/General/Release_Notes|DESK-MX6UL-L Release Notes] kit by using a simple bash script.
Note: Starting from this release the support for the SPL has been introduced in U-Boot. Previous versions of this script will no longer produce a fully functional and bootable microSD card.

The procedure has been tested on a Linux PC running Ubuntu LTS (>=16.04) distribution with

• a 16 GB microSD card [1]
• the binary files delivered along with the DESK-MX6UL-L 1.0.1

The resulting card is partitioned as depicted here below:

• bootable partition (mmcblk0p1, vfat) containing:
  • binary images (u-boot and kernel images)
• root file system partition (mmcblk0p2, ext3)
  • root file system binaries and init scripts

The script - named mksd.sh - can be realized with the following code:

#!/bin/bash

if [[ -z $1 || -z $2 || -z $3 || -z $4 || -z $5 ]]
then
	echo "$0 Usage:"
	echo "	$0 <device> <u-boot.img> <SPL> <binaries directory> <rootfs tar.bz2>"
	echo "	Example: $0 /dev/sdc u-boot.img SPL binaries/ rootfs.tar.bz2"
	exit
fi

if [ "$(whoami)" != "root" ]
then
	echo "you must be root to run this script!"
	exit
fi

if ! [[ -b $1 ]]
then
	echo "$1 is not a valid block device!"
	exit
fi

if ! [[ -e $2 ]]
then
	echo "Incorrect u-boot.img location!"
	exit
fi

if ! [[ -e $3 ]]
then
	echo "Incorrect SPL location!"
	exit
fi

if ! [[ -d $4 ]]
then
	echo "Incorrect Binaries location!"
	exit
fi

if ! [[ -f $5 ]]
then
	echo "Incorrect rootfs location!"
	exit
fi

DRIVE=$1
if [[ "$DRIVE" == *"mmcblk"* ]]
then
	echo "You're using a mmc device, I need to fix partition names"
	PART="p"
else
	PART=""
fi
UBOOT=$2
SPL=$3
BINARIES=$4
RFS=$5

echo "All data on "$DRIVE" now will be destroyed! Continue? [y/n]"
read ans
if ! [ $ans == 'y' ]
then
	exit
fi

echo "[Partitioning $1...]"

dd if=/dev/zero of=$DRIVE bs=1024 count=1024

SIZE=`fdisk -l $DRIVE | grep Disk | awk '{print $5}'`

echo DISK SIZE - $SIZE bytes

CYLINDERS=`echo $SIZE/255/63/512 | bc`

# check if we're running an old (e.g. 2.20.x) or new (e.g. 2.24.x) sfdisk
sfdisk --help | grep -- -H

if [ "$?" -eq "0" ]
then
	{
		echo 40,1380,0x0c,*
		echo 1420,,83,-
	} | sfdisk -D -H 255 -S 63 -C $CYLINDERS $DRIVE
else
{
    echo 16M,8176M,0x0c,*
    echo 8192M,,83,-
} | sfdisk $DRIVE
fi

partprobe


echo "[Making filesystems...]"
mkfs.vfat -F 32 -n BOOT "$DRIVE$PART"1 #> /dev/null
mkfs.ext3 -F -L ROOTFS "$DRIVE$PART"2 #> /dev/null

echo "[Copying files...]"

binaries_dir=${BINARIES%/}
mount "$DRIVE$PART"1 /mnt
cp -av --no-preserve=ownership $binaries_dir/* /mnt/
umount "$DRIVE$PART"1

echo "[Extracting rfs (this may take a while...)]"
mount "$DRIVE$PART"2 /mnt
tar jxf $RFS -C /mnt > /dev/null
chmod 755 /mnt
umount "$DRIVE$PART"2

echo "[Programming SPL]"
dd if=$SPL of=$DRIVE bs=512 seek=2 conv=fsync

echo "[Programming u-boot.img]"
dd if=$UBOOT of=$DRIVE bs=1k seek=69 conv=fsync

echo "[Done]"

Here is an example that shows how to use this script. Let's assume that the binary files were downloaded in the desk subdirectory of the working directory. Before invoking the script, the following files has to be renamed in order to make them compatible with the default U-Boot environment variables:

• bootscript: boot.scr
• Linux kernel: uImage
• Device tree blob: imx6ul-lynx-som0013-cb002f.dtb (or imx6ul-axelulite-cb003a.dtb or imx6ul-axelulite-cb006c.dtb)

This is the list of the binary files that will be used by the script:

ll /tftpboot/desk-mx-l/

You can now run the script, by passing the following parameters:

• Device file of the microSD card (/dev/sdb in the example)
• U-Boot image
• SPL
• Path of the directory containing the bootscript file, the Linux kernel image, and the device tree blob files
• Archive of the target's root file system (compressed as .tar.bz2 file).

dvdk@vagrant:~/desk-mx-l$ ./mksd.sh /dev/sd<x> <u-boot.img> <SPL> <binaries_dir>/ <rfs_filename>
...
...
...

[1] In case you have a different size, you'll need to change the sfdisk parameters accordingly.

bootscr

Once you got the new binaries compiled from your modified sources, they have to be installed on first SD partition preserving the original file names used into boot.scr u-boot bootscript.

Here below there is an example on how to create a boot.scr file from the bootscript.txt for booting from SD card:

echo 'bootscript generated with command "mkimage -A ARM -T script -C none -n DESK-MX6UL -d bootscript.txt boot.scr"'

setenv desk_release 'desk-mx6ul-l-1.0.1'

if test 0x${som_configid#} = 0x00000013 && test 0x${cb_configid#} = 0x0000002f;
then
    setenv fdtfile ${desk_release}_imx6ul-lynx-som0013-cb002f.dtb
elif test 0x${cb_configid#} = 0x0000003a
then
	setenv fdtfile ${desk_release}_imx6ul-axelulite-cb003a.dtb
elif test 0x${cb_configid#} = 0x0000006c
then
	setenv fdtfile ${desk_release}_imx6ul-axelulite-cb006c.dtb
else
    echo Invalid CB! Autoreset ...
    sleep 30
	reset
fi

setenv bootfile ${desk_release}_uImage

setenv mmc_loadk 'fatload mmc ${mmcdev}:1 ${loadaddr} ${bootfile}'
setenv mmc_loadfdt 'fatload mmc ${mmcdev}:1 ${fdtaddr} ${fdtfile}'

echo Booting DESK-MX6UL via mmcboot with ${fdtfile} as device tree

run mmcboot

echo mmcboot FAILURE

and compile it using:

mkimage -A ARM -T script -C none -n DESK-MX6UL -d bootscript.txt boot.scr

Then copy the boot.scr into the <binaries_dir> directories used by the script to create the SD card.

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