Mailing List Archive: isolinux source, detecting 8086 cpu

isolinux source, detecting 8086 cpu

Feb 27, 2002, 6:44 PM

Post #1 of 3 (1467 views)

Hi, I was looking through isolinux and noticed you had trouble detecting
8086 cpu's. I have some experience with this so I thought you might
like some different info. The behavior of the "push sp" instruction
changed after the 8086 to pushing sp before updating it. I've included
a snippet of one of my bootstraps in case you want to use it (or just
want to understand better). I also use a different method for detecting
the 386. Basically I just attempt a 32-bit instruction and hook the
invalid opcode exception. Hope this helps. :)

Mike

push sp
; save sp
pop ax
; ax = saved sp
cmp ax, sp
; 8086 modifies sp before pushing
je .not_8086
; processor is not an 8086

;
.invalid_cpu: ;
mov si, .err_cpu ; si
points to error message
jmp .error_handler ;
display message and reboot

;
.not_8086:
;
mov W [6 << 2], .invalid_cpu ; store offset of
invalid opcode handler
mov [(6 << 2) + 2], cs ; store
segment of handler
xor eax, eax
; test a 32-bit instruction

isolinux source, detecting 8086 cpu [ In reply to ]

hpa at zytor

Feb 27, 2002, 8:49 PM

Post #2 of 3 (1258 views)

Permalink

Michael K Ter Louw wrote:

> Hi, I was looking through isolinux and noticed you had trouble detecting
> 8086 cpu's.

... ? ...

The only comment is "I hope this catches 80186 CPU's as well"... I'm
well aware of the push sp thing and the code uses it.

(FWIW, 80186's *should* be handled correctly by my code. Not that it
matters AT ALL for anything but SYSLINUX, since no system exists which
would be affected otherwise...)

-hpa

isolinux source, detecting 8086 cpu [ In reply to ]

hpa at zytor

Feb 27, 2002, 9:46 PM

Post #3 of 3 (1258 views)

Permalink

Michael K Ter Louw wrote:
>
> BTW, I'm thinking of using isolinux/memdisk for a project I'm working
> on. I was wondering if you or anyone else had started working on the
> simple API for COMBOOT images yet. If not, I'm thinking of going at it.
>
> At this point I need at least the ability to instruct isolinux to boot
> an image with memdisk. Beyond that I would like to use the open
> file/getc/ungetc functions, maybe implement an unfiltered getline, and
> possibly make a findfirst/findnext routine for listing directories.
>

The sensible thing would be to implement a subset of the DOS API (INT
21h), so that it could be invoked either via COMBOOT or from DOS
directly. I have looked at it several times, but it's been one of those
things "in case there is ever interest."

-hpa