Bug (or at least a limitation) in CUBE / Fat File System found and solved

[mycall]

I hope this is a good place for this.

I had difficulty getting an SD card read to work with FATFs code generated by CUBE. The file at first appeared to get corrupted after about 20K bytes and I spent considerable time trying to figure out what I was doing wrong.

It turned out to be an issue with the function sd_read_block in file sd.c. Specifically there is a call to sd_delay with an argument of 5. This would cause 5 nulls to be sent to the SD card to pump its internal state machine. In my case I needed to change the delay to 10.

Using Windows 10, CUBE version 5.6.1 and Keil 5.34.0.0.

My SD card is embedded in the HW and I am unable to get to it so I can't report the brand but it is a 4GB card.

I hope this helps someone else.

[BParh.1]

Thanks @mycall​  for the initiative to potentially help other developers to save form potential trouble :thumbs_up:

[Amel NASRI]

Hi @mycall​ ,

Thanks for reporting this issue.

In order to confirm it and fix it for all other users who may face such a problem, could you please;

• confirm that issue is still there with latest STM32CubeMX version?
• precise the selected STM32 part number?

-Amel