I am making a PS1 Memcard using a Teensy 2.0 and SD card. The memcard receives commands 52(read), 57(write) and 58(read that this command is for checking if a Pocketstation is inserted). The cmd 52 implementation is somewhat complete(shows all saves on Browser). I'm still working on cmd 57(in-game saving but no copying in Browser). For cmd 58 I haven't found anything other that it is 5 bytes long and that returning 0 at every byte appears as a Pocketstation.
So if anyone knows anything about these commands specially about cmd 58(the return values from Sony Memcard and Pocketstation) and if there is a time to read and write to SD card other than in between bytes received.