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Suggestion: Work around Xi8088 BIOS bug by setting DS = 40h for 13.41 call #156
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Sounds reasonable. That is directly related to my question on the developer mailinglist some time ago to what DS should be set in this case. There is a (closed) related FDISK issue FDOS/fdisk#80. I may implement setting DS as well for FDISK.
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on May 11, 2024 Has this still not been added yet?
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on Oct 10, 2025 Added a Pull Request with this change: #224
@boeckmann It appears you patched fdisk in FDOS/fdisk@8126a21 - right?
@boeckmann It appears you patched fdisk in FDOS/fdisk@8126a21 - right?
At least that was the intention. I think I tested it via 86box.
The FAT12/FAT16 loaders using either CHS or LBA set
dsto 1FE0h:Line 210 in e3bfd6a
So it corrupts the
byte [1FE0h:41h]which is at linear 1FE41h, at 127 KiB. That's within the allocation for a large FAT or a large kernel file. If the FAT and file both are smaller, or the FAT entry that ends up at this address isn't used, then it will appear to work despite the memory corruption.SYS also uses 13.41:
Line 1265 in e3bfd6a
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on Oct 10, 2025 - added a commit that references this issue
on Oct 10, 2025 - added a commit that references this issue
on Nov 11, 2025
Circling back to the Xi8088 BIOS bug that affected at least some revisions of the Book8088:
The bug was described in http://www.bttr-software.de/forum/forum_entry.php?id=21275
This is where the kernel may call a ROM-BIOS that doesn't support LBA to detect that it doesn't support LBA:
kernel/kernel/initdisk.c
Lines 651 to 657 in 1b6de0f
My idea is to force DS = 40h for this call, which will work around the bug of the BIOS writing to offset 41h without setting up DS.
I didn't have this idea yet because my use of 13.42 without the proper 13.41 check call makes this more difficult, however I just added a workaround to the Xi8088 bug to the callers that are not as size constrained as the lDOS boot sector loaders, eg lDOS iniload: https://hg.pushbx.org/ecm/ldosboot/rev/4c929733a229
(I will upload a blog post that also addresses this later.)