Compute Module 4: eMMC vs Lite issues

I have been trying to set up a CM4 Lite module with a standard ROM, and have hit some issues. It seems that anything after about February 2023 no longer works with the Lite version, but works perfectly with the eMMC versions. After a very frustrating six hours, having tried several versions of both firmware and the ROM with several peices of hardware, here is where I’ve ended up:

5.28 (Feb 2022) – works with Lite versions – SD card shows up as SDFS::4
5.29 (Dec 2020) – works with Lite versions – SD card shows up as SDFS::4
5.29 (Feb 2023) – does not work with Lite – “disc drive is empty”
5.29 (23 July 2023) – does not work with Lite – “disc drive is empty”

5.28 (Feb 2022) – does not work with eMMC versions – no drive seen
5.29 (Dec 2020) – does not work with eMMC versions – no drive seen
5.29 (Feb 2023) – works with eMMC – eMMC shows up as SDFS::0
5.29 (23 July 2023) – works with eMMC – eMMC shows up as SDFS::0

In all failing cases, it manages to boot to the BootFX screen, and drops to the Supervisor prompt. Any attempt to check the disc comes up with a “disc drive is empty” error.

In all working cases, as long as SDFSDrive is set to the number shown above, it boots normally.

What’s happenend?! Can anyone else replicate confirm my findings, perhaps with 5.28 and the recent nightly ROM?

5.28 (Feb 2022) – works with Lite versions – SD card shows up as SDFS::4
5.29 (Dec 2020) – works with Lite versions – SD card shows up as SDFS::4
5.29 (Feb 2023) – does not work with Lite – “disc drive is empty”
5.29 (23 July 2023) – does not work with Lite – “disc drive is empty”

5.29 (Feb 2023) – works with eMMC – eMMC shows up as SDFS::0
5.29 (23 July 2023) – works with eMMC – eMMC shows up as SDFS::0

In all failing cases, it manages to boot to the BootFX screen, and drops to the Supervisor prompt.

Before 1 Feb 2023 the rom does not support eMMc. So ignore ROMS before this date (excluded above).

Before June 2023 recent revisions were not known so GPIO module stayed dormant.

Feb 2023 and Jul 2023 ROMs do work on Lite with suitable SD cards, all ID’d as SDFS::0.

Booting as far as the supervisor prompt reads the SD card using the EEPROM firmware.

Reading the SD card using RISC OS or Linux fails on certain card types listed at https://elinux.org/RPi_SD_cards

ROMS after Sep 2022 seem to bork on CM4 Lite with SD cards larger than 16GB (work on earlier roms but identify as SDFS::4 which does not affect booting). Those before Feb 2023 can’t see eMMc.

After quite a bit of to-ing and fro-ing with Chris by email, it looks like newer ROMs are very sensitive to the card in use on the Lite model.

SanDisk ones seen to work at 32GB and 16GB but Kioxia ones don’t, and neither do some Samsung ones.

It all seems a bit too picky…

Have you found any cards that work that are 64GB or larger? Some 32GB cards are SDHC and some are SDXC: below this size are SDHC and above this size are SDXC. I have tried a Samsung 128GB card and it works on roms before the Jan 2023 changes but will not read under roms after 1 Feb 2023.

Is it this commit here that broke it? ‘Back out part-implemented DDR support for eMMC devices’ which got eMMc working on the Pi CM4.

Have you found any cards that work that are 64GB or larger?

Nope. Tried a 64GB Kioxia, a 64GB Kingston, and a 256GB Samsung Evo (green one) – all dropped to Supervisor. To be fair, I tried a 4GB SanDisk Class 4 and that didn’t work either.

Is it this commit here that broke it?

The date seems about right. But beyond that, I’d be largely clueless.

Have you found any cards that work that are 64GB or larger? Some 32GB cards are SDHC and some are SDXC: below this size are SDHC and above this size are SDXC. I have tried a Samsung 128GB card and it works on roms before the Jan 2023 changes but will not read under roms after 1 Feb 2023.

So far as I can tell, the only difference between the two is that SDHC is natively formatted FAT32 and SDXC natively formatted exFAT. Both of which you blow away when you write Pi disc image to the card. So that itself doesn’t matter, but it may be that different cards support different speeds, and maybe one of those doesn’t work.

It worked prior tothe commit, but not afterwards. Reverting to pre commit rm and SD card works again.

Have you found any cards that work that are 64GB or larger?

I have now! I took a punt on buying a 128GB version of the same model of SanDisk card that worked at 16GB and 32GB, and lo and behold – it works! So this looks like it only works with a very small subset of SDs, and much smaller subset than works with the Pi 4. I wonder if the author of that commit used the same card?

After quite a bit of to-ing and fro-ing with Chris by email, it looks like newer ROMs are very sensitive to the card in use on the Lite model.

This makes an interesting story and an updated rom and firmware can be downloaded whilst the various bug fixes work their way through the system. The last of these has now been merged (three hours ago!) so daily roms should contain these fixes from tomorrow.