Raspberry mmc hat

Good morning, I apologize for my bad english. I have recently bought this product https://www.8086.net/product/mmc-hat. It does work with raspberry pi os (model 3b+) but it does not work on risc os (sd cards inserted aren’t accessible, I can only see sd card 0).
Does anyone know how to use the hat on risc os? I am not quite sure how to debug …

Welcome!

Your English is almost faultless so far, better than many “native” contributors! Very picky people would want RISC OS in capitals, and English traditionally has a leading capital when a language.

None of these things affect the clarity of your posting. I hope someone with the necessary expertise to assist you will arrive soon.

Reading the description of the MMC-Hat, it sounds like the RPi actually has more than one SD card controller inside, and the MMC-Hat attaches to the second.

So it would need changes to SDFS to handle more than one controller on the RPi. I guess. Waiting for Jeffrey, Sprow or Ben to go into the details…

I seem to recall that the second SDIO was significantly nobbled. I looked into it when the first Compute module came out and concluded that it couldn’t effectively be used. It appears things have changed on later Pi’s.

Hello, thank you all for the answers. I was afraid it would not be a simple fix. Rewriting parts of RISC OS (thank you John) to support this particular piece of hardware is too much to ask.
Good night and I hope you all had a nice weekend.