Den Tue, 09 Apr 2019 20:03:49 +0200 skrev Michał Pleban <lists_at_michau.name>: > Ruud_at_Baltissen.org wrote: > > > Only today I found the part that determines how many drives are in > > the machine. The only thing I can (I think) is to compare all > > instructions one by one just in case my tool (or better: I as the > > programmer) made a mistake. > > What I would normally do would be to step through this code with a > debugger, once with a VGA card and once without, and see where they > differ. I agree. The PC20-III is probably similar enough to any standard PC compatible that you can run it's BIOS ROMs in some emulator, so you don't have to attach some kind of hardware debugger. I would however suggest trying to patch the 33 F6 / 31 F6, 2B CF / 29 F9 things to match the original rom. Although unlikely they might had used some parts of the ROM for both data and code. At least one byte should be possible to save here and there if a code block ends with the same byte as a data block starts with or the other way around. Btw I'd suggest trying to poke around in RAM to see if you can make it believe that it indeed has two drives and if both drives work. If only one drive work, then it's not really a problem with the detection but rather actual access to the second drive. Side track re PC and more than one drive: It would be a nice hack if someone would patch the bios of a 286 or higher to work with 4 drives. Not sure what it would be good for, but the original PC/XT floppy controller can use four drives but that only works with an XT class bios. The same card in a 286 or newer can only use the first two drives. Kind of useless to have more than two drives with a hard disk as that controller only can use DD format, but still :) -- (\_/) Copy the bunny to your mails to help (O.o) him achieve world domination. (> <) Come join the dark side. /_|_\ We have cookies.Received on 2020-05-29 21:37:44
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