int 13 and el torito floppy boot image

Hi, I'm hoping someone here has some El Torito experience. I'm using
mkisofs to burn a bootable CDROM of the colorForth operating system as
if it were a 1.44MB floppy. I could probably get it to work by setting
-boot-load-size to the full image, but for various reasons I'd like to
avoid that, and my reading of the spec doesn't give me any reason to
believe I'd have to resort to that.

However, when I attempt to read the first cylinder with this code:

mov ebx, iobuffer
mov ax, (2 8) + 36 ;# 18 sectors per head, 2 heads
mov dx, 0x0000 ;# head 0, drive 0
mov ch, [cylinder + loadaddr]
mov cl, 1 ;# sector number is 1-based, and we always read from
first
int 0x13

int 13 returns with carry set, and AX=0124 (36 sectors read, and
"invalid function in AH or invalid parameter". The iobuffer is all
zeroes after the read.

I may well be doing something wrong, but meanwhile I'd like to find
out if anybody has made this work by treating the virtual floppy as a
real one, and using int 13 to read blocks from the CDROM. Thanks -- jc

On Apr 27, 10:43 pm, jcomeau_ictx wrote:
Hi, I'm hoping someone here has some El Torito experience. I'm using
mkisofs to burn a bootable CDROM of the colorForth operating system as
if it were a 1.44MB floppy. I could probably get it to work by setting
-boot-load-size to the full image, but for various reasons I'd like to
avoid that, and my reading of the spec doesn't give me any reason to
believe I'd have to resort to that.


I beginning to think it's not just my programming, especially since it
boots from a floppy with no problem. I downloaded the win98 boot disk
from http://freepctech.com/pc/002/files010.shtml, made an ISO image
using:

mkisofs -b win98.img -c boot.catalog -o win98.iso README.txt

Bochs can boot it, as it can my colorForth ISO. VMware cannot boot
either, which I don't think is a bug in VMware, it usually does just
what my laptop would do. I guess I could waste another CD and check
but I'm pretty sure my laptop won't boot win98 from the CDROM either.
Are there a bunch of buggy El Torito BIOSes out there? Hard to
believe, this many years after the spec was published.