stm32L5 SDMMC interface as memory card

[ChrisP]

Moin,

is it possible to run the stm32L5 Series mcus (or other stm32s) not in SDMMC host mode, but be used like a normal SDcard for storage?

I looked over the documentation and only found host mode descriptions. I feel like I missed some details, so greatly appreciate pointers.

Cheers

[Tesla DeLorean]

No, this generally requires IP to act as a state machine, or buffering/protocol engine.

You could be a SPI slave, and respond/interface that way, but the performance would be incredibly lackluster.

[ChrisP]

Thanks!

I had the naive assumption it "should" be possible and hence kept looking.

Cheers

[Tesla DeLorean]

Generally specialized devices used as NAND controllers, or interfacing WiFi controller IC.

The mechanics could probably be plumbed via an FPGA/CPLD, but STM32 parts don't really provide for an external DMA interface (ie inbound/outbound interface to internal memories), but only an external memory interface into which you could map your own peripherals or memory buffers.

SPI would be a means to act like a faux SD Card, but generally the effort would be high and the rewards low, and why there's probably no pre-package solution

[ChrisP]

yes. totally agree. Once I realized sdmmc was running at 25MHz I started to have doubts. Without the corresponding (lacking) IP it will just be a mess. A small fpga will most likely be used in this project then.

I will try it with SPI for fun, but I doubt to get meaningful results in terms of speed and will push it to weekend project with an stm32.

Thanks again!