TS-7840 eMMC Controller

This board includes a Micron eMMC module. Our off the shelf builds are 4GiB, but up to 64GiB are available for larger builds. The eMMC flash appears to Linux as an SD card at /dev/mmcblk0. Our default programming will include one partition programmed with our Debian image.

The CPU boots out of the emmc's hardware boot partitions /dev/mmcblk0boot0 and /dev/mmcblk0boot1. These are both 16MB, and are separate from the mmcblk0 flash. Erasing or manipulating /dev/mmcblk0 and its partitions will not affect these hardware partitions. The board boots to /dev/mmcblk0boot0 by default, but boot1 can be selected if it has been written with a valid bootloader. This allows atomic updates in the field of u-boot, but should only be done with care as it can leave your board not booting if a bad image is written before switching the active boot partition.

WARNING:

This may need a development board or RMA to recover the board if the CPU fails to boot. Make certain a valid u-boot is present on a boot device before switching to it.

Write a u-boot to mmcblk0boot1 with:

echo 0 > /sys/block/mmcblk0boot1/force_ro
dd if=/path/to/u-boot.kwb bs=1M of=/dev/mmcblk0boot1

Once the data has been verified as written, the active boot partition can be switched to mmcblk0boot1:

# The argument after enable should be 2 for mmcblk0boot1, or 1 for mmcblk0boot0
mmc bootpart enable 2 1 /dev/mmcblk0

The active partition can be read as part of the extcsd read:

mmc extcsd read /dev/mmcblk0