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eMMC

The MitySOM-QC6490 Development Kit has an eMMC (U3) that can be used for additional storage when booting from UFS and (in the future) as a boot media itself.

Caveats

  • Rev 1 and 2 of the MitySOM-QC6490 Development Kit does not have provisions to power the eMMC before the MitySOM-QC6490 is powered, which means eMMC cannot be used a boot media for these boards. Rev 3 of the MitySOM-QC6490 Development Kit will have this resolved.
  • Rev 1 and 2 of the MitySOM-QC6490 Development Kit does not have a return clock connected on SDC1 interface, thus limiting the eMMC interface to HS200 speeds. Rev 3 of the MitySOM-QC6490 Development Kit has this resolved.

Development Board Configuration

Ensure that Switch S5 is set properly.
  • Switch 1 should be set to enable MEM-EN, which is a top level enable to send 1.8 V to the eMMC
  • Switch 2 can be either set or not set
    • If Switch 2 is not set the 1.8V comes from the DC supply on the Development Kit
    • If Switch 2 is set the 1.8V comes from the SOM

Usage as Additional Storage

Device Enumeration

eMMC will always appear as /dev/mmcblk0. You can use lsblk to verify the device is recognized: 

root@qcs6490-mitysom-devkit:~# lsblk | grep mmcblk0
mmcblk0      179:0    0  58.3G  0 disk 
mmcblk0boot0 179:32   0     4M  1 disk 
mmcblk0boot1 179:64   0     4M  1 disk

Note that if you do not see mmcblk0, please verify the steps in Development Board Configuration were followed.

Partitioning, Formatting and Mounting

fdisk is recommended for partioning the eMMC.

We will move forward creating a single partition of the full size of the eMMC:
  1. Run the command fdisk /dev/mmcblk0.
  2. Type o and press enter.
  3. Type n and press enter.
  4. Press enter.
  5. Press enter.
  6. Press enter.
  7. Press enter.
  8. The next step will commit all changes; ensure there was no remaining data on the eMMC card that you need.
  9. Type w and press enter. A full transcript of the above partitioning steps should look something like the following:
    root@qcs6490-mitysom-devkit:~# fdisk /dev/mmcblk0

Welcome to fdisk (util-linux 2.39.3).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Command (m for help): o
Created a new DOS (MBR) disklabel with disk identifier 0x22119e45.

Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): 

Using default response p.
Partition number (1-4, default 1): 
First sector (2048-122314751, default 2048): 
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-122314751, default 122314751): 

Created a new partition 1 of type 'Linux' and of size 58.3 GiB.

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

lsblk can be used to verify the partition was created.

root@qcs6490-mitysom-devkit:~# lsblk | grep mmcblk0
mmcblk0      179:0    0  58.3G  0 disk 
`-mmcblk0p1  179:1    0  58.3G  0 part 
mmcblk0boot0 179:32   0     4M  1 disk 
mmcblk0boot1 179:64   0     4M  1 disk

Now you can make a file system on the eMMC partition you created.

We will move forward with an ext4 file system. 

root@qcs6490-mitysom-devkit:~# mkfs.ext4 /dev/mmcblk0p1 
mke2fs 1.47.0 (5-Feb-2023)
Discarding device blocks: done                            
Creating filesystem with 15289088 4k blocks and 3825664 inodes
Filesystem UUID: 149deef9-6556-48c6-9d1b-a158b6d0ccf8
Superblock backups stored on blocks: 
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
        4096000, 7962624, 11239424

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (65536 blocks): done
Writing superblocks and filesystem accounting information: done

You can now use the mount command to mount your partition:

root@qcs6490-mitysom-devkit:~# mount /dev/mmcblk0p1 /mnt 
root@qcs6490-mitysom-devkit:~# ls -l /mnt
lrwxrwxrwx    1 root     root            16 Oct 21  2025 /mnt -> var/rootdirs/mnt
root@qcs6490-mitysom-devkit:~# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/mmcblk0p1           57.1G      2.0M     54.2G   0% /var/rootdirs/mnt
root@qcs6490-mitysom-devkit:~# mount | grep mmcblk0
/dev/mmcblk0p1 on /var/rootdirs/mnt type ext4 (rw,relatime)

Performance

If you want to benchmark the eMMC, fio is a highly flexible benchmarking utility that comes installed on the MitySOM-QC6490 Development Kit. You can read more at the link, but below is a basic fio commands (which assumes eMMC partition is mounted to /mnt) for testing read and write performance:

fio --name=emmc --filename=/mnt/emmctest --size=1G --bs=256k --iodepth=4 --numjobs=1 --ioengine=libaio --direct=1 --rw=write --loops=5 --verify=crc32c

Additional Information from debugfs

You can get additional information on eMMC via debugfs. First, mount debugfs.

mount -t debugfs none /sys/kernel/debug/

The mmc0/ios file supplies data on the interface speed. For eMMC operating at HS200 you should expect to see the following:
root@qcs6490-mitysom-devkit:~# cat /sys/kernel/debug/mmc0/ios 
clock:          200000000 Hz
actual clock:   192000000 Hz
vdd:            18 (3.0 ~ 3.1 V)
bus mode:       2 (push-pull)
chip select:    0 (don't care)
power mode:     2 (on)
bus width:      3 (8 bits)
timing spec:    9 (mmc HS200)
signal voltage: 1 (1.80 V)
driver type:    0 (driver type B)

Usage as Boot Media

Caveats

  1. The following instructions require you have a MitySOM-QC rev4 or greater and MitySOM-QC Development Board rev4 or later.
  2. Critical Link BSP 1.2, and previous releases, do not support UFS as additional storage once booted from eMMC.
    1. Support for this is currently under investigation.

If you have any questions please post them on the forums.

Prepare the Hardware

  • Set the BOOT select pins (S1) as seen below
  • Set the eMMC power selection (S5) as seen below
  • Set the DC EN SRC switch (S15) as seen below

Prepare the Software Image

  1. Acquire a copy of the software image to program eMMC with (for example a pre-built qcom-multimedia-image from Repositories and Pre-built Images)).
    1. Note: This image will need to be modified so make a copy if preserving the original state is desired.
  2. Enter the image directory (e.g. qcom-multimedia-image) and run the follow command: 
    1.  cp ./partition_emmc/gpt_main*.bin ./partition_emmc/gpt_backup*.bin ./partition_emmc/rawprogram[0-9].xml ./partition_emmc/patch*.xml ./partition_emmc/zeros_*sectors.bin ./

Program the CDT

  1. Make and enter a cdt_emmc directory 
    1. mkdir cdt_emmc
    2. cd cdt_emmc
  2. Copy files from the BSP cdt directory: 
    1. cp {bsp_directory}/cdt/mitysom-qc6490-devkit_CDT.bin . 
    2. cp {bsp_directory}/cdt/prog_firehose_ddr.elf .
  3. Copy files from the qcom-multimedia-image directory: 
    1. cp {qcom-multimedia-image_dir}/partition_emmc/gpt_*1* . 
    2. cp {qcom-multimedia-image_dir}/rawprogram1.xml . 
    3. cp {qcom-multimedia-image_dir}/patch1.xml .
  4. Modify the copied ‘rawprogram1.xml’ with a text editor of choice to point at the CDT binary: 
    1. -- <program start_sector="34" size_in_KB="4.0" physical_partition_number="1" partofsingleimage="false" file_sector_offset="0" num_partition_sectors="8" readbackverify="false" filename="" sparse="false" start_byte_hex="0x4400" SECTOR_SIZE_IN_BYTES="512" label="cdt"/>
++ <program start_sector="34" size_in_KB="4.0" physical_partition_number="1" partofsingleimage="false" file_sector_offset="0" num_partition_sectors="8" readbackverify="false" filename="mitysom-qc6490-devkit_CDT.bin" sparse="false" start_byte_hex="0x4400" SECTOR_SIZE_IN_BYTES="512" label="cdt"/>
  5. Program the ‘cdt’ with QDL:
    1. Use lsusb to verify the system is in QDL mode.
    2. {path_to_qdl}/qdl --storage emmc prog_firehose_ddr.elf rawprogram1.xml patch1.xml
    3. Successful programming should look similar to the following:
      waiting for programmer...
flashed "cdt" successfully                                                                                               
flashed "PrimaryGPT" successfully
flashed "BackupGPT" successfully
13 patches applied                                                                                                      
no boot partition found

Program Filesystem, etc.

  1. Change directory back into the qcom-multimedia-image directory and program with QDL:
    1. Use lsusb to verify the system is in QDL mode.
    2.  {path_to_qdl}/qdl --storage emmc prog_firehose_ddr.elf rawprogram0.xml patch0.xml
    3. Successful programming should look similar to the following:
      waiting for programmer...
flashed "xbl_a" successfully                                                                                             
flashed "xbl_b" successfully
flashed "dtb_a" successfully at 65536kB/s                                                                               
flashed "dtb_b" successfully at 32768kB/s                                                                               
flashed "efi" successfully at 40329kB/s                                                                                 
flashed "xbl_config_a" successfully                                                                                      
flashed "xbl_config_b" successfully
flashed "xbl_ramdump_a" successfully
flashed "uefi_a" successfully                                                                                           
flashed "shrm_a" successfully
flashed "tz_a" successfully                                                                                             
flashed "tz_b" successfully                                                                                             
flashed "aop_a" successfully
flashed "aop_b" successfully
flashed "hyp_a" successfully
flashed "hyp_b" successfully                                                                                            
flashed "imagefv_a" successfully
flashed "imagefv_b" successfully
flashed "uefisecapp_a" successfully
flashed "uefisecapp_b" successfully
flashed "multiimgoem_a" successfully
flashed "cpucp_a" successfully
flashed "devcfg_a" successfully
flashed "devcfg_b" successfully
flashed "qupfw_a" successfully
flashed "qupfw_b" successfully
flashed "toolsfv" successfully
flashed "system" successfully at 41339kB/s                                                                               
flashed "PrimaryGPT" successfully
flashed "BackupGPT" successfully
13 patches applied
partition 0 is now bootable
  2. Boot the SOM, but note that this boot will take longer than normal as you will need to wait for some timeouts (~2 minutes).
  3. Make modification to prevent the timeouts from occurring in the future:
    1. Login
    2. mount -o remount, rw /usr
    3. rm /usr/lib/systemd/system/local-fs.target.wants/var-usbfw.mount
    4. rm /usr/lib/systemd/system/var-usbfw.mount
  4. Reboot
  5. Login and verify you are booted from eMMC. 
    1.  df -h | grep -w "/"
    2. You should see root is mounted to mmcblk0p67:
      /dev/mmcblk0p67          36.7G      3.9G     31.1G  11% /

References

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