Boot Linux operating system from the SD card

You can boot up Qualcomm development kits from the SD card.

1. Prepare the SD card by flashing it with efi.bin and rootfs.img.
2. Insert the prepared SD card into the SD card slot of the development kit.

The development kit boots up from the SD card, which contains a backup or redundant operating system to ensure continuous operation.

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Supported platforms

To prepare a bootable SD card, do the following: Prerequisites Use a Linux desktop system to perform steps 1 through 5 and prepare a bootable SD card. Procedure

1. Verify the device node for the inserted SD card on any Linux system, for example, /dev/mmcblk1 or /dev/mmcblk2.
2. To format the SD card, run the mkfs.ext4 <sdcard slot> command on the Linux terminal. In the following example, the dev node for the SD card is /dev/mmcblk1.
   mkfs.ext4 /dev/mmcblk1
   
   Output:
   mke2fs 1.46.5 (30-Dec-2021)
   Found a dos partition table in /dev/mmcblk1
   Proceed anyway? (y,N) y
   Discarding device blocks: done
   Creating filesystem with 3889536 4k blocks and 972944 inodes
   Filesystem UUID: 069e04f8-0b72-4a94-aa93-f5ec03bea38d
   Superblock backups stored on blocks:
      32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208
   Allocating group tables: done
   Writing inode tables: done
   Creating journal (16384 blocks): done
   Writing superblocks and filesystem accounting information: done
   
3. Use the fdisk command to create two partitions on the SD card to copy efi.bin and rootfs.img.
   1. Create the first partition with the vfat file system to copy efi.bin. To create the partition, run the following command (for example, the dev node is /dev/mmcblk1): In this example, leave the First sector field empty and ensure that Last sector is large enough to copy efi.bin.
      fdisk /dev/mmcblk1
      
      Output:
      Welcome to fdisk (util-linux 2.37.4).
      Changes will remain in memory only, until you decide to write them.
      Be careful before using the write command.
      The device contains 'ext4' signature and it will be removed by a write command.
      See fdisk(8) man page and --wipe option for more details.
      Device doesn't contain a recognized partition table.
      Created a new DOS disklabel with disk identifier 0xa5fa6b03.
      Command (m for help): n
      Partition type
         p   primary (0 primary, 0 extended, 4 free)
         e   extended (container for logical partitions)
      Select (default p): p
      Partition number (1-4, default 1): 1
      First sector (2048-31116287, default 2048):
      Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-31116287, default 31116287): +512M
      Created a new partition 1 of type 'Linux' and of size 512 MiB.
      Command (m for help): w
      The partition table has been altered.
      Calling ioctl() to re-read partition table.
      Syncing disks.
      
      To convert the partition to the vfat file system, run the following command:
      mkfs.vfat /dev/mmcblk1p1
      
      Output:
      mkfs.fat 4.2 (2021-01-31)
      
   2. Create the second partition with the ext4 file system to copy rootfs.img as follows: To create the partition, run the following command (for example, the dev node is /dev/mmcblk1): In this example, leave the First sector field empty and ensure that Last sector is large enough to copy rootfs.img.
      fdisk /dev/mmcblk1
      
      Output:
      Welcome to fdisk (util-linux 2.37.4).
      Changes will remain in memory only, until you decide to write them.
      Be careful before using the write command.
      Command (m for help): n
      Partition type
         p   primary (1 primary, 0 extended, 3 free)
         e   extended (container for logical partitions)
      Select (default p): p
      Partition number (2-4, default 2): 2
      First sector (1050624-31116287, default 1050624):
      Last sector, +/-sectors or +/-size{K,M,G,T,P} (1050624-31116287, default 31116287): +10G
      Created a new partition 2 of type 'Linux' and of size 10 GiB.
      Command (m for help): w
      The partition table has been altered.
      Calling ioctl() to re-read partition table.
      Syncing disks.
      
      To convert the partition to the ext4 file system, run the following command:
      mkfs.ext4 /dev/mmcblk1p2
      
      Output:
      mke2fs 1.46.5 (30-Dec-2021)
      Discarding device blocks: done
      Creating filesystem with 2621440 4k blocks and 655360 inodes
      Filesystem UUID: 9e470d01-77fe-4382-a273-ab8b022bdd8b
      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
      
4. Verify the partitions were created:
   lsblk -f /dev/mmcblk1
   
   Output:
   NAME FSTYPE FSVER LABEL UUID                                 FSAVAIL FSUSE% MOUNTPOINTS
   mmcblk1
   |
   |-mmcblk1p1
   |    vfat               1EAC-8FF8
   `-mmcblk1p2
        ext4               9e470d01-77fe-4382-a273-ab8b022bdd8b
   
5. Copy efi.bin and rootfs.img from the successfully built Qualcomm Linux image on the host computer to the partitions on the SD card. Run the following commands on the host computer:
   • dd if=<path>/efi.bin of=<sdcard slot> bs=4M
   • dd if=<path>/rootfs.img of=<sdcard slot> bs=4M To copy both images from the /tmp path, following is an example of how to copy them to the SD card: In this command, the dev node for the SD card is /dev/mmcblk1.
   dd if=/tmp/efi.bin of=/dev/mmcblk1p1 bs=4M
   dd if=/tmp/rootfs.img of=/dev/mmcblk1p2 bs=4M
   

Result The SD card is now ready to be used as boot media for a Qualcomm Linux development kit. When an SD card is inserted, it is used as fallback boot media only if the primary flash storage (UFS or eMMC) on the development kit is unbootable.

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Simulate an unbootable condition

To verify that the SD card is used as fallback boot media, you can force the primary flash storage (UFS or eMMC) into an unbootable state by erasing its EFI partition. Perform the following steps on the development kit while it’s still running from the primary storage, before inserting the SD card:

1. Log in to the development kit over the UART console or SSH.
2. Confirm the EFI partition is exposed as /dev/disk/by-partlabel/efi. This partition name comes from the --name=efi entry in the partitions.conf file for your platform. For more information, see Manage partitions in Qualcomm Linux.
   ls -l /dev/disk/by-partlabel/efi
   
3. Erase the EFI partition by overwriting it with zeros:
   dd if=/dev/zero of=/dev/disk/by-partlabel/efi bs=4M
   
4. Insert the prepared SD card into the SD card slot and reboot the development kit. Because the EFI partition on the primary storage is now erased, the bootloader falls back to booting from the SD card.