Hi, the LBA detection of the FAT12/FAT16 boot sectors (both for the FreeDOS and "OEM" kernels) could misdetect that a BIOS does support LBA if it doesn't really. This is the used code (after calling Int13.41 for the boot unit):
> shr cx, 1 > ; CX must have 1 bit set > sbb bx, 0aa55h - 1 > ; tests for carry (from shr) too! > jne read_normal_BIOS This test succeeds if (cx&1) && (bx==AA55h) as intended but also succeeds if (!(cx&1)) && (bx==AA54h). This is a highly unlikely case but nonetheless an error which should be corrected. Example: > sub bx, 0AA55h > jne read_normal_BIOS > shr cx, 1 > jnc read_normal_BIOS Note that the code after this expects bx to be zero, so sub must be used here instead of cmp. I exchanged the order of the test for cx bit 0 (disk access support) and the correct signature in bx since it's easier to understand the code this way. (It would work the other way around as well.) Regards, Christian ------------------------------------------------------------------------------ Join us December 9, 2009 for the Red Hat Virtual Experience, a free event focused on virtualization and cloud computing. Attend in-depth sessions from your desk. Your couch. Anywhere. http://p.sf.net/sfu/redhat-sfdev2dev _______________________________________________ Freedos-kernel mailing list Freedos-kernel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-kernel
