I am using a STM32H743 to access a SD card using the ST micro driver code. I m NOT using interrupts for the MMC however if an interrupt occurs during a file access the code sometimes crashes. By crashes I mean the read routine times out.

[BBert]

Why isn't the SDMMC code tolerant to interrupts?

[TDK]

> Why isn't the SDMMC code tolerant to interrupts?

Because the hardware needs to be fed data (or have data read) with strict timing requirements to avoid overrun/underrun of the hardware buffer.

Disable interrupts during access or use DMA based accessing to avoid.

[Tesla DeLorean]

The FIFO adds some tolerance, but you can't go wandering off in the middle of the data transfer phase, the cards just don't have a mid-transfer abort protocol..

Figure you're interrupt routines are very tardy, or you're task switching to some completely alternate universe.

Use DMA, polled is very fragile, as I think I've expressed here multiple times.

[BBert]

Hi TDK,

Thanks for the quick reply. I have disabled interrupts during the read access which, as you said, solved the problem. However it raised a new problem. If the interrupts are disabled then the timeout, which uses the systick interrupt, no longer works :( I have not used DMA so far but I'm willing to try it. Do you have any examples showing how to use DMA with the SDMMC?

Thanks...

[Tesla DeLorean]

There should be example diskio drivers in the FatFs Middleware directories.

H7 going to want to be conscious of the memory being utilized, the alignment and cache coherency.

[BBert]

Hi Tesla,

I have searched all of the FatFs directories (including Middleware) for an example using DMA but I cannot find a single one :(

[AScha.3]

Hi Bert,

i was searching also (about 4 minutes) and see: sd_diskio_dma.c

(in STM32CubeH7-master\Projects\STM32H747I-EVAL\Applications\FatFs\FatFs_Dual_Instance\CM7\Src ) .

Maybe this is what you want.

😉

[BBert]

Hi AScha.3,

Thanks for the reply 🙂

The example you mentioned is for a dual-core STM32H7 device but it may work for my needs. I'll give it a try as time permits.