[syslinux] MEMDISK without floppy drive

[Robert Wruck]

I tried to use memdisk 2.06 to boot a floppy image on my notebook which 
doesn't have a floppy drive.

The boot failed, because the bootstrap code tried to reset the floppy 
drive (int13, ah=00). Memdisk passes reset calls on to the original 
int13 handler, which returns failure, because there is no floppy drive 
to reset (#1).

Also i noted that some boot records (notably some created by win9x) use 
the extended int13 calls (ah=4x) without checking for presence (ah=41).
memdisk doesn't implement those (#2).


Workaround for #1: only hand reset calls down to the original handler if 
it is meant for hard disks, too (high bit in dl set).

i added the following lines to the Reset code:

Reset:
	TRACER 'R'
	test dl,80h
	jnz .passon
	xor ax,ax
	ret

.passon:
	[ original Reset code here ]


Workaround for #2: I implemented the int13 ah=41,42,43,44,47 and 48 
functions (not well tested, though!).
If someone is interested in those, i could post the patch.

cheers,
robert