Until now, my understanding of the PERCOM block (and send percom command) was that this block configures the drive with selected parameters.
If any of the parameters is wrong, percom block is discarded. If parameters match one of the drive's densities, they are set hard, until next
put percom. So after setting the drive to FM with put_percom command, the drive sits there in FM until commanded otherwise by another PUT PERCOM.
Is that understanding OK?
If configuration is read by percom, and not by get status, Mydos does not see the difference between
SD and ED other way than by sectors per track number. FM/MFM flag is discarded.
So if you have ED disk, and boot mydos off it, the percom block that is sent to the drive is
for the FM/ED (which is wrong). So the dos cannot read DUP.SYS because the drive is already in FM and the disk is ED.
Perhaps FM/MFM flag ( Percom.bit2 ) in PERCOM should be discarded? I don't know, it's there for a reason.
How does the original PERCOM drive handle this?