[Freedos-devel] stack setup in BIOS, prior to loading FreeDOS

[<reh...@gm...>]

I am working to get FreeDOS running on my 286 system. As part of this, I am
trying to improve my BIOS code. As I look at the stack setup when the system
initializes, I am using the following.

	; org 0x0000
	xor		ax,	ax
	mov		ds, 	ax
	mov		bp, 	0x8000
	mov		ss,	ax
	mov		sp,	bp
	mov		ax, 	0xf000				; ROM data
	mov		es,	ax

Based on https://en.wikibooks.org/wiki/X86_Assembly/Bootloaders and
https://github.com/kaneton/appendix-bios (and as I understand it), 0x8000 is
used for bp and sp upon system initialization. I expect FreeDOS changes the
location of the stack multiple times during boot as the boot sector is
loaded/moved and as the kernel is loaded.

Am I OK with the stack setup I am using prior to loading FreeDOS, or should
I consider a different/better approach?

Thanks!

Rich


; *286 system physical memory map*
; -------------------------------
; -       ROM  (256 KB)		-
; -      0xC0000-0xFFFFF		-
; -------------------------------
; -   I/O & Expansion  (64 KB)	-
; -      0xB0000-0xBFFFF		-
; -------------------------------
; -       VIDEO  (64 KB)		-
; -      0xA0000-0xAFFFF		-
; -------------------------------
; -       RAM  (640 KB)		-
; -      0x00000-0x9FFFF		-
; -------------------------------
;
; **************************************
; from boot32lb.asm (fat32 lba):
;	...
;	|-------| 		1FE0:7E00
;	|BOOTSEC|
;	|RELOC.|
;	|-------| 		1FE0:7C00
;	...
;	|-------| 		2000:0200
;	|  FAT  | 		(only 1 sector buffered)
;	|-------| 		2000:0000
;	...
;	|-------| 		0000:7E00
;	|BOOTSEC| 		overwritten by the kernel, so the
;	|ORIGIN | 		bootsector relocates itself up...
;	|-------| 		0000:7C00
;	...
;	|-------|
;	|KERNEL| 		maximum size 134k (overwrites bootsec
origin)
;	|LOADED| 		(holds 1 sector directory buffer before
kernel load)
;	|-------| 		0060:0000
;	...