I would like this thread to become a "How to do it" tutorial thread.
I had sorta hoped spin2 might be ready but it seems it's still a way off.
As an exercise I am going to use a modified version of Kye's FAT Driver that I use in my P1 Prop OS.
It has a couple of extra spin calls, and I have the P2 PASM cog driver version of the P1 PASM driver working.
For reference: I have attached the whole P1 OS v114 source but we are interested in _SD_FAT2.spin (reduced version of _SD_FAT.spin) and _SD_PASM.spin (P2ASM working without interface to _SD_FAT).