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

History
Version	Issue Date	Notes
1.0.1	Jun 2021	First DESK release
3.0.0	Feb 2022	3.0.0 DESK release

How to create a bootable SD card

The procedure described here was tested with a virtual machine such as the MVM. The USB controller of the MVM should be enabled by default. If you are using Linux-based distribution and are having trouble detecting a USB device in virtual machine, please make sure your user belongs to the vboxusers group.

This article shows how to create a bootable microSD for the DESK-MX6UL-L Release Notes kit by using a simple bash script.
Note: Note: Starting from DESK-MX6UL-L 1.0.1 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 MVM released with DESK-MX6-L 3.0.0 release with

• a 16 GB microSD card [1]
• a USB SD card reader
• the binary files delivered along with the DESK-MX6UL-L 3.0.0

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. We use here files delivered with DESK-MX6UL-L 3.0.0 release. 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
• splash image: splash_image.bmp
• Linux kernel: desk-mx6ul-l-3.0.0_uImage
• Device tree blob: desk-mx6ul-l-3.0.0_imx6ul-axelulite-cb003a.dtb.

We will copy them into ~/desk-mx-l/desk directory. Needed binary files can be found on MVM in the following location:

dvdk@vagrant:~$ ll /tftpboot/desk-mx-l/
total 12180
drwxr-xr-x 2 dvdk root    4096 Feb 27 18:54 ./
drwxr-xr-x 3 dvdk root    4096 Feb 27 18:52 ../
-rw-r--r-- 1 dvdk root   32441 Feb 27 18:54 desk-mx6ul-l-3.0.0_imx6ul-axelulite-cb003a.dtb
-rw-r--r-- 1 dvdk root   31479 Feb 27 18:54 desk-mx6ul-l-3.0.0_imx6ul-axelulite-cb006c.dtb
-rw-r--r-- 1 dvdk root   32518 Feb 27 18:54 desk-mx6ul-l-3.0.0_imx6ul-lynx-som0013-cb002f.dtb
-rw-r--r-- 1 dvdk root   44032 Feb 27 18:52 desk-mx6ul-l-3.0.0_mx6uldesk_axelulite_spi_SPL
-rw-r--r-- 1 dvdk root  600280 Feb 27 18:52 desk-mx6ul-l-3.0.0_mx6uldesk_axelulite_spi_u-boot.img
-rw-r--r-- 1 dvdk root   44032 Feb 27 18:52 desk-mx6ul-l-3.0.0_mx6uldesk_axelulite_SPL
-rw-r--r-- 1 dvdk root  600280 Feb 27 18:52 desk-mx6ul-l-3.0.0_mx6uldesk_axelulite_u-boot.img
-rw-r--r-- 1 dvdk root   44032 Feb 27 18:52 desk-mx6ul-l-3.0.0_mx6uldesk_lynx_spi_SPL
-rw-r--r-- 1 dvdk root  564844 Feb 27 18:52 desk-mx6ul-l-3.0.0_mx6uldesk_lynx_spi_u-boot.img
-rw-r--r-- 1 dvdk root   44032 Feb 27 18:52 desk-mx6ul-l-3.0.0_mx6uldesk_lynx_SPL
-rw-r--r-- 1 dvdk root  564244 Feb 27 18:52 desk-mx6ul-l-3.0.0_mx6uldesk_lynx_u-boot.img
-rw-r--r-- 1 dvdk root   44032 Feb 27 18:52 desk-mx6ul-l-3.0.0_mx6uldesk_lynx_usb_SPL
-rw-r--r-- 1 dvdk root  457216 Feb 27 18:52 desk-mx6ul-l-3.0.0_mx6uldesk_lynx_usb_u-boot.img
-rw-r--r-- 1 dvdk root 8189464 Feb 27 18:54 desk-mx6ul-l-3.0.0_uImage
dvdk@vagrant:~$ ll ~/desk-mx-l/desk-mx6ul-l-3.0.0_boot.scr
-rw-rw-r-- 1 dvdk dvdk 936 Feb 28 07:36 /home/dvdk/desk-mx-l/desk-mx6ul-l-3.0.0_boot.scr
dvdk@vagrant:~$ cp /tftpboot/desk-mx-l/desk-mx6ul-l-3.0.0_uImage ~/desk-mx-l/desk/desk-mx6ul-l-3.0.0_uImage
dvdk@vagrant:~$ cp /tftpboot/desk-mx-l/desk-mx6ul-l-3.0.0_imx6ul-axelulite-cb003a.dtb ~/desk-mx-l/desk/desk-mx6ul-l-3.0.0_imx6ul-axelulite-cb003a.dtb
dvdk@vagrant:~$ cp /tftpboot/desk-mx-l/splash_image.bmp ~/desk-mx-l/desk/
dvdk@vagrant:~$ cp ~/desk-mx-l/desk-mx6ul-l-3.0.0_boot.scr ~/desk-mx-l/desk/boot.scr

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$ sudo ./desk-mx6ul-l-3.0.0_mksd.sh /dev/sdb /tftpboot/desk-mx-l/desk-mx6ul-l-3.0.0_mx6uldesk_axelulite_u-boot.img /tftpboot/desk-mx-l/desk-mx6ul-l-3.0.0_mx6uldesk_axelulite_SPL ~/desk-mx-l/desk ./rfs/desk-mx6ul-l-3.0.0_dave-image-devel-desk-mx6ul.tar.bz2 
All data on /dev/sdb now will be destroyed! Continue? [y/n]
y
[Partitioning /dev/sdb...]
1024+0 records in
1024+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 2.05358 s, 511 kB/s
DISK SIZE - 15931539456 bytes
Checking that no-one is using this disk right now ... OK

Disk /dev/sdb: 14.86 GiB, 15931539456 bytes, 31116288 sectors
Disk model: Transcend       
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

>>> Created a new DOS disklabel with disk identifier 0x3adbf72f.
/dev/sdb1: Created a new partition 1 of type 'W95 FAT32 (LBA)' and of size 8 GiB.
/dev/sdb2: Created a new partition 2 of type 'Linux' and of size 6.9 GiB.
/dev/sdb3: Done.

New situation:
Disklabel type: dos
Disk identifier: 0x3adbf72f

Device     Boot    Start      End  Sectors  Size Id Type
/dev/sdb1  *       32768 16777215 16744448    8G  c W95 FAT32 (LBA)
/dev/sdb2       16777216 31116287 14339072  6.9G 83 Linux

The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.
[Making filesystems...]
mkfs.fat 4.1 (2017-01-24)
mke2fs 1.45.5 (07-Jan-2020)
Creating filesystem with 1792384 4k blocks and 448800 inodes
Filesystem UUID: 3f65294a-899d-417c-9092-e8bf209ec6b2
Superblock backups stored on blocks: 
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done 

[Copying files...]
'/home/dvdk/desk-mx-l/desk/boot.scr' -> '/mnt/boot.scr'
'/home/dvdk/desk-mx-l/desk/desk-mx6ul-l-3.0.0_imx6ul-axelulite-cb003a.dtb' -> '/mnt/desk-mx6ul-l-3.0.0_imx6ul-axelulite-cb003a.dtb'
'/home/dvdk/desk-mx-l/desk/desk-mx6ul-l-3.0.0_uImage' -> '/mnt/desk-mx6ul-l-3.0.0_uImage'
'/home/dvdk/desk-mx-l/desk/splash_image.bmp' -> '/mnt/splash_image.bmp'
[Extracting rfs (this may take a while...)]
[Programming SPL]
86+0 records in
86+0 records out
44032 bytes (44 kB, 43 KiB) copied, 0.0930599 s, 473 kB/s
[Programming u-boot.img]
586+1 records in
586+1 records out
600280 bytes (600 kB, 586 KiB) copied, 1.64853 s, 364 kB/s
[Done]

[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-3.0.0'

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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