FWIW I hacked together something here for reading a 1571 with an U64. https://github.com/michielboland/c64stuff/blob/master/asm/serial.s (Build with vasm - you will also need bootstrap.s from the same repo, or just clone the whole thing and type make.) Reading a 360K floppy with interleave=4 takes about 1m52s. (see picture) Cheers Michiel
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