Can I use a CM3 without eMMC on a RPi CM4 carrier board?

#1

I have a Radxa CM3 v1.31A without eMMC, which I had hoped to use in a Raspberry Pi CM4 carrier board. However, I am unable to get it to boot, and judging from other people’s reports it seems there may be an actual fuck-up at the hardware level which renders the Radxa CM3 incompatible with the RPi CM4.
Is this true? If so, there is malfeasance on Radxa’s part, because the advertisement for the Radxa CM3 strongly implies it is a drop-in replacement for the Rpi CM4!

#2

It is an replacement on the HW side, which means you should not see “blue smoke” when you attach it. It should be capable of drive all the HW on the IO board, but it is not SW compatible. Neither you can boot Raspbian OS nor can use unmodified SW written for RPi CM4. There is even no 32bit userland by default. And honestly, I have not seen such a promise from Radxa (but I don’t read marketing “info” in general). Last but not least, I cannot find a variant without EMMC, it should always have a SPI flash and 8-128GB of soldered EMMC.

#3

Thank you for your reply. There is a variant without eMMC; checkout https://shop.allnetchina.cn/products/rock3-computing-module?variant=39486826709094
What I hear from your reply is that I shouldn’t be waiting for the Rock CM3 to eventually get proper support but instead I should be looking at alternatives, right?

#4

No. You should prepare for making your hands dirty by checking the SW for dependencies on the RPi platform and remove them before you switch. And that will happen with any other alternative too if it would not be a clone of the RPi. It is very similar HW, but by far not the same.

#5

But it doesn’t even boot using the images provided by Radxa! This seems to be a hardware problem, where the Rock CM3 can only be used with Radxa’s own IO board.

#6

To be honest, that could be, I have no clue if an EMMC less CM3 can boot from a CM4 base board. And it might be dead, that’s also true. I don’t think the CM4 io board support the Maskrom mode of the CM3 board, so probably fill an RMA.

#7

It should:

https://wiki.radxa.com/Rock3/installusb-install-radxa-cm3-rpi-cm4-io

So you could try this to check if the CM3 is alive.