Suggestion: Work around Xi8088 BIOS bug by setting DS = 40h for 13.41 call

[ecm-pushbx]

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

	/* check for LBA support */
	regs.b.x = 0x55aa;
	regs.a.b.h = 0x41;
	regs.d.b.l = drive;
	regs.flags = FLG_CARRY; /* ensure carry is set to force error if unsupported */
	init_call_intr(0x13, &regs);

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.)

[boeckmann]

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.