Hello.
I hope this is the right place to post this problem.
I hope someone can help me with this problem.
I am writing a bios extension program (for 386+) and I need to create variable data in RAM. (Bios extension does not org 100h a local stack and pushing the variables onto the system stack won't work due to there being several hundred bytes of various sized data.)

what I would like to do it movsb all the data declarations from the rom to Ram. This is what I have, but manipulating the data and printing it to the display does not show any changes to the data occurring. Is there a better solution?

; movsb all the data to 8000h
pushad
push ds
push es

mov ax,8000h
mov es,ax ; now es and ax are pointing to the same place.
lea si,[begindata]
lea di,[begindata]
mov cx,812 ; 812 bytes ; move 300 bytes to ram - plus 512 bytes for buffer. (512 = 256 Dwords)
rep movsb ; move 100 bytes to 8000H
; end of movsb all the data to 8000h


Then I immediately change the variables, store them, and print them.

mov bx,01
xor bx,1021h
mov [storewd],bx
mov ax,[storewd]
call prntAX

mov bx,02
xor bx,1021h
mov [crc],bx
mov ax,[storewd]
call prntAX



I read somewhere that user accessible RAM starts at 80,000. That does not seem to work either.

Any help or advice is appreciated

Thank you and best regards

I'm may be wrong here but the only BIOS locations I know of are:

0x00400 - 0x00600
0x9FC00 - 0xA0000 (this can vary)
0xE0000 - 0xFFFFF

----

The accessible range is 0x00000 - 0xFFFFF unless you have less than 1MB of RAM.

Looking at your code, you've set es to 0x8000 which translates to linear address 0x80000 but your print routines don't access this buffer and simply move the constant 0x1020 to ax every time; you'd have to do something like mov ax, word [es:0].

I got the answer from someone. I have to set ds to the 8000 that's in es after the movsb: push es and pop ds. Now ds points to 8000h and the expansion rom chip now has dynamic RAM variables instead of static ROM values located at label begindata $ (for a total of 812 bytes of variable.)

Thank you cod3b453.

Now that that is resolved, Int 13 AH,42 returns ah=01, invalid parameter

mov ax,08000h ;8000h
mov es,ax ; now es and ax are pointing to the same place.
lea si,[begindata]
lea di,[begindata]
mov cx,812 ; bytes ; move 300 bytes to ram - plus 512 bytes for iobuff. (512 = 256 Dwords)
rep movsb ; move 100 bytes to 8000H
push es ; this pushed 812 onto the stack
pop ds ; now pop 8000h off the stack - ds now points to 8000h

mov dl,80h ; hard disk 1
lea si,[lbaio] ; lbaio
mov ah,42h ;read
int 13h
jc notok <<< jumps to Not Ok

>>> never gets here <<<<<<
Ah returns as 01
01h invalid function in AH or invalid parameter

Can anyone explain why this might be?

int 13h, AH 42h
parameters

dl-Drive number
ds:si-segment and offset to DAP

512 Bytes is 128 Dwords (in the x86-style of DWORD)

mov cx, 812
rep movsb

the movsb doesn't update ES it updates SI and DI..
the rep updates CX (at the end of the movsb it becomes zero).

Thank you typedef and BAiC. I'm a noob. I've got manuals to read! Like, what is the DAP?

As I read your response again I see: SI and DI!

So Int 13 return is telling the truth. The destination buffer parameter is not valid.

Thanks again!

calculating ROM addresses vs. physical addresses isn't particularly difficult.

it's information that's needed most of all: Where are you trying to Read From and where are you trying to write to?

The formula, by the way, is 16*Segment + LinearAddress.

Hi BAiC
Int 13 ah42 reads the hard disk 01 and should be putting the 512 byte sector idata nto lbaio. (I used 812 bytes to allow creation of additional variable data to be used above the 512 hd data: indexes, counts, strings, etc.) lbaio and other variables are declared in the ROM, but rom is an OTP with no stack or data space so I had to movsb it to RAM, which is where all the trouble starts!

Hi ouadji
No os, or maybe the bios uses a version of DOS assembly language. I'm programming a bios extension device.

I've been experimenting with how to set si and ds to point to the 8000h offset for use with int 13 ah42 hard drive read with no success. I always get ah=01 invalid parameter. does anyone have any ideas?

No matter what I set ds and si to I get that same error code.

push ds
push es

mov ax,08000h ;8000h
mov es,ax ; now es and ax are pointing to the same place.
lea si,[begindata]
lea di,[begindata]
mov cx,812 ; bytes ; move 300 bytes to ram - plus 512 bytes for iobuff. (512 = 256 Dwords)
rep movsb ; move 100 bytes to 8000H

mov ax,08000h ;8000h
mov es,ax ; now es and ax are pointing to the same place.
push es ; this pushed 800h onto the stack
pop ds ; now pop 8000h off the stack - ds now points to 8000h


mov dl,80h ; hard disk 1
lea si,[lbaio] ; lbaio
mov ah,42h ;read
int 13h

jc notok

ret

move variables first then code.

destination address=0800h

label_vars:
myword dw ? ;2 bytes here
mystring db 'hello world',0 ; 12 bytes here, 14 bytes total.

first copy those to ram @ SI like this. note this is rather slow than just using rep movsb.
mov si,label_vars
mov di,08000h ; segment + offset
mov cx,14
@@:
lodsb
cmp cx,0
je @F
movsb
dec cx
jmp @B
@@:
; now when in ram, myword will be at 08000h linear and my string will be at 08003h linear

your code should start at 080012h linear