BIOS detection of floppy disk drives? \ VOGONS

BIOS detection of floppy disk drives?

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First post, by superfury

Posted on 2015-09-13, 13:40

superfury Offline

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How does the BIOS detect the amount of floppy disk drives attached to a floppy disk controller? In my emulator it always detects 4 floppy disk drives, instead of the 2 drives installed (A and B) when port 62&63 contain 0xFF by default, and no drives when 62&63 contain 0x00 by default.

Anyone knows what the correct value should be?

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Reply 1 of 4, by superfury

Posted on 2015-09-13, 16:02

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I've fixed the problem: For two floppy drives, PPI port 0x62 needs bit 2 set and bit bit 3 cleared (bit 2 meaning 2 floppy disks and bit 3 meaning 3/4 floppy disks when set). Although for some reason all sources of the PPI port 0x62 tell me that it's supposed to be bit 6&7?

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UniPCemu for Android, Windows, PSP, Vita and Switch on itch.io

Reply 2 of 4, by Jepael

Posted on 2015-09-13, 18:53

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What? For a real IBM PC5150, it is bits 6&7 (and 0) on port 0x60. But to read the switches instead of keyboard scancode shift register, the port 0x61 bit 7 must be set to one.

0x61&128==0 -> scancode on port 0x60
0x61&128==128 -> SW1 on port 0x60

Reply 3 of 4, by vladstamate

Posted on 2015-09-13, 19:42

vladstamate Offline

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I do not think he is emulating a 5150 but rather a 5160 (XT) hence he needs the port 63 to convey number of floppy disks. Basically you have to be careful what your BIOS is expecting: IBM PC vs IBM PC XT vs IBM PC AT, as they all report floppies differently.

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Reply 4 of 4, by superfury

Posted on 2015-09-14, 04:46

superfury Offline

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vladstamate wrote:
I do not think he is emulating a 5150 but rather a 5160 (XT) hence he needs the port 63 to convey number of floppy disks. Basically you have to be careful what your BIOS is expecting: IBM PC vs IBM PC XT vs IBM PC AT, as they all report floppies differently.

Vlad.

It's indeed a PC XT system (or AT BIOS when a 80286 processor is selected).

Author of the UniPCemu emulator.
UniPCemu Git repository
UniPCemu for Android, Windows, PSP, Vita and Switch on itch.io

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