Just a quick update: After spending a few hours playing with the Adafruit version of TinyUSB for Arduino, I can now see a Psion SSDs as block devices in Linux!

The status is:

• ROM SSDs: Readable, but no FEFS drivers in Linux. However, DD works fine, so you can use SIBOIMG to extract files.
• Flash SSDs: Same as ROM SSDs. No writing as yet because I haven't implemented that in libsibo.
• RAM SSDs: These are FAT formatted so they can be mounted directly in Linux! Fully readable, although a few weird issues like files showing up twice (see the screenshot below). Writing is a mess: ASIC4 SSDs corrupt on write, ASIC5 SSDs just ignore writes. This could be a timing issue on my part, where the code is just going too fast for the RAM chips.

This is a screenshot of a RAM SSD mounted from /dev/sda (note: no partition table on these), being read by Linux like it was just another USB drive.

So yeah, this is the closest I've come to having an actual USB SSD Drive. I have a lot to learn about TinyUSB, as I feel like I'm just scratching the surface of its potential. I also still need to write the routines for writing to Flash I and Flash II SSDs in libsibo, plus rig up a 17.5v supply. I'm also quite far into designing a test PCB with through-hole components.

More to come soon!