eMMC
An embedded Multi-Media Card (eMMC) flash device is populated on the phyCORE-AM62x SOM as a programmable nonvolatile storage. The eMMC flash is connected to the MMC0 8-bit interface of the phyCORE-AM62x, which supports the JEDEC eMMC electrical standard v5.1. This guide will show how to view partition information, read from, and write to the eMMC featured on the phyCORE-AM62x SOM. To learn more information about the phyCORE-AM62x eMMC flash memory, please see section 6.1.3 in the Hardware Manual.
Note
In order to follow this guide your phyCORE-AM62x development kit must be booting from SD Card.
Viewing eMMC Partition Information
You can verify the eMMC partitions by using the following command to list the partition information of known MMC devices:
Target (Linux)fdisk -l
Expected OutputDisk /dev/mmcblk1: 15 GB, 15931539456 bytes, 31116288 sectors 243096 cylinders, 4 heads, 32 sectors/track Units: sectors of 1 * 512 = 512 bytes Device Boot StartCHS EndCHS StartLBA EndLBA Sectors Size Id Type /dev/mmcblk1p1 * 16,0,1 1023,3,32 2048 264191 262144 128M c Win95 FAT32 (LBA) /dev/mmcblk1p2 1023,3,32 1023,3,32 264192 2330587 2066396 1008M 83 Linux Disk /dev/mmcblk0: 30 GB, 31826378752 bytes, 62160896 sectors 485632 cylinders, 4 heads, 32 sectors/track Units: sectors of 1 * 512 = 512 bytes Device Boot StartCHS EndCHS StartLBA EndLBA Sectors Size Id Type /dev/mmcblk0p1 * 16,0,1 1023,3,32 2048 273063 271016 132M c Win95 FAT32 (LBA) /dev/mmcblk0p2 1023,3,32 1023,3,32 274432 5799513 5525082 2697M 83 Linux Disk /dev/mmcblk0boot0: 31 MB, 33030144 bytes, 64512 sectors 1008 cylinders, 4 heads, 16 sectors/track Units: sectors of 1 * 512 = 512 bytes Disk /dev/mmcblk0boot0 doesn't contain a valid partition table Disk /dev/mmcblk0boot1: 31 MB, 33030144 bytes, 64512 sectors 1008 cylinders, 4 heads, 16 sectors/track Units: sectors of 1 * 512 = 512 bytes Disk /dev/mmcblk0boot1 doesn't contain a valid partition table
As can be seen in the above Example Output, this eMMC has already been formatted with a data partition, /dev/mmcblk0p1. To follow the rest of this guide, one data partition will be required.
If you did not see a /dev/mmcblk0p* partition refer to the following commands in order to create one:
Warning
Be careful using the “fdisk” command. If you aren’t careful, it can easily delete a partition of a flash device you didn’t intend to, and this could be your root filesystem! Just be sure to specify /dev/mmcblk0, not the SD card you are booting from.
fdisk /dev/mmcblk0
# Enter into fdisk interactive session:
# Use the following commands in order to create a Linux partition.
n # create new partition
p # partition type
1 # partition number
2048 # first sector
30777310 # last sector
t # change partition type
83 # linux filesystem
w # write changes
Now reboot the system and you should see the eMMC device mounted automatically in the following steps.
Target (Linux)reboot
Setup a Root Filesystem on the eMMC
In order to interact with the eMMC, the eMMC has to be partitioned and a rootfilesystem needs to be setup.
Create a ext4 type root filesystem
Target (Linux)mkfs.ext4 /dev/mmcblk0p1
Expected Outputroot@phyboard-lyra-am62xx-3:~# mkfs.ext4 /dev/mmcblk0p1 mke2fs 1.45.7 (28-Jan-2021) /dev/mmcblk0p1 contains a vfat file system labelled 'boot' Proceed anyway? (y,N) y Discarding device blocks: done Creating filesystem with 135508 1k blocks and 34000 inodes Filesystem UUID: 2cb4ccd0-ea94-4c61-a547-bdd264c6d600 Superblock backups stored on blocks: 8193, 24577, 40961, 57345, 73729 Allocating group tables: done Writing inode tables: done Creating journal (4096 blocks): done Writing superblocks and filesystem accounting information: done
Mounting the eMMC
Mount the eMMC to a volatile tmp folder
Writing to eMMC
Reading from the eMMC
Use the copy (cp) or move (mv) command to put this file back onto your SD card.
Target (Linux)cp /tmp/emmc/test.txt ~/test-READ.txt
Make sure the file was not corrupted during the transfer using md5sum.