f_open returns FR_OK but doesn't create a file

[WellLeithed]

I'm simply trying to do:

res = f_open(&fil, "file.txt", FA_CREATE_ALWAYS | FA_WRITE);

but nothing is created despite the return message. Could it be my SD card? I'm able to read from it in 4B mode.

Any suggestions would be gratefully received.

[WellLeithed · Accepted solution]

It turns out that it was as simple as enabling hardware flow control in the MX. I had been unable to get it to mount without the clock divider being 4, but I imagined that may have been creating timing issues as I see the recommended value is 0. May this have caused underrun issues that hardware flow control can prevent?

Thanks for all your willingness to help.