MMC problems on (some?) SD cards

[tlongeri]

Commands on the SD Card do not work correctly when sent immediately after a response or after , without clocking the card by sending 0xFF through SPI. I was getting error status responses from the card for perfectly good commands. This Stack Overflow answer helped me solve this after spending hours on the problem. It seems this is only a problem with some SD cards (at least that's what the Stack Overflow answer suggests): I imagine it was tested on one that didn't suffer from this clocking requirement.

I was using a 16gb SanDisk Ultra SD Card (mounted on an Adalogger Featherwing).

For now I will leave my dirty debugging code that did manage to fix the problem for me, and will update when I have time to make it into something cleaner.