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 [SOLVED] Setting es:bp 
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Joined: Mon Oct 26, 2009 2:33 pm
Posts: 38
Location: United Kingdom
Post [SOLVED] Setting es:bp
Hi guys,

I'm going back and changing some of my previous boot code and things to make them better. Now back when I started I would output status messages to the screen like this:

Loading 2nd Stage Bootloader [ Ok ]

Now to do this I was manually loading each character into memory and calling Int 0x10 / AH = 0x09.

This worked fine but was horrendously rubbish.

What I want to do is use Int 0x10 / AH = 0x13, having loaded a pointer to a string into ES:BP.

This is what I have so far:

mov cx, #21
mov bh, #0x0
mov bl, #0x1f

mov bp, #mymsg
mov ah, #0x13
mov al, #%00000001

int 0x10.

The message part

mymsg:
.byte 13,10
.ascii "Welcome To PandoraOS"

Now this works....sort of.

It displays in the correct colour etc, but it displays the wrong characters, it's obviously pointing to some random place in memory.

I'm using as86 and can't find a good example.

I'm being stupid, please correct me.

Cheers,

_________________
Andy Esser
neogenix Broadcast


Last edited by AndyEsser on Sat Nov 14, 2009 3:08 pm, edited 1 time in total.



Wed Nov 04, 2009 3:09 pm
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Joined: Sat Jul 25, 2009 7:44 am
Posts: 274
Location: United Kingdom
Post Re: Setting es:bp
I always remember using MOV SI, String

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Thank you for reading,

Kieran C G Foot


Thu Nov 05, 2009 4:20 am
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Joined: Mon Oct 26, 2009 2:33 pm
Posts: 38
Location: United Kingdom
Post Re: Setting es:bp
Nope, no joy.

I think I'm missing something obvious.

Cheers,

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Andy Esser
neogenix Broadcast


Thu Nov 05, 2009 1:51 pm
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Post Re: Setting es:bp
you did not load ES
fixed:
Code:
mov ax,cs ;here is where you went wrong
mov es,ax
mov cx, #21
mov bh, #0x0
mov bl, #0x1f
mov bp, #mymsg
mov ah, #0x13
mov al, #%00000001
int 0x10.


Sat Nov 07, 2009 2:46 am

Joined: Mon Oct 26, 2009 2:33 pm
Posts: 38
Location: United Kingdom
Post Re: Setting es:bp
Sadly I'm still no closer.

I've tried with snippets of other people's code for printing strings etc and still nothing. I'll post my entire assembly program and see whether someone can show me what i'm doing wrong.

I'm assembling with

as86 boot.asm -o bootloader.o
ld86 -d bootloader.o -o bootloader
Code:
entry start

start:
mov ah, #0x02
xor bh, bh
int 0x10

mov ax, cs
mov es, ax
mov cx, #21
mov bx, #0x001f
mov ax, #0x1301
mov bp, #mymsg

int 0x10

mymsg:
.ascii "Welcome to PandoraOS"
.byte 0

_________________
Andy Esser
neogenix Broadcast


Sat Nov 07, 2009 3:05 pm
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Post Re: Setting es:bp
what if you replace
Code:
.ascii "Welcome to PandoraOS"
.byte 0

with
Code:
db 'Welcome to PandoraOS'
db 0

i just dont trust the assembler


Sat Nov 07, 2009 7:40 pm

Joined: Mon Oct 26, 2009 2:33 pm
Posts: 38
Location: United Kingdom
Post Re: Setting es:bp
I get an error

"Junk after operands" and it's pointing to the W after the '. It doesn't happen on the db 0 line though.

Should I use a different assembler? NASM or something?

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Andy Esser
neogenix Broadcast


Sun Nov 08, 2009 6:21 am
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Joined: Sat Jul 25, 2009 11:26 am
Posts: 81
Post Re: Setting es:bp
The deal is that both ES and DS must be zeroed out (xor ax, ax / mov es, eax / mov ds, eax <-- alternatively, use "ax" instead of "eax" if you're generating code for 16-bit machines and can't get a size override prefix).

Another common problem is that people know better how programs like notepad work rather than how the video card does. You need to point to the string itself "13h 10h" is not by any means a new line sequence. If you want a new line you need to get the current cursor position, clear the column, increment the row and set the cursor again.

Cheers,
Bogdan


Mon Nov 09, 2009 1:17 am
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Joined: Mon Oct 26, 2009 2:33 pm
Posts: 38
Location: United Kingdom
Post Re: Setting es:bp
Hi mate,

Thanks for the suggestions. I've done that, but still no joy. Just random characters displayed. Grr. This is getting frustrating now.

I was a little dubious about the 13, 10 and I've now replaced it with a 0 so that the string is 'null-terminated' for later use.

Any other suggestions?

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Andy Esser
neogenix Broadcast


Mon Nov 09, 2009 11:13 am
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Joined: Mon Oct 26, 2009 2:33 pm
Posts: 38
Location: United Kingdom
Post Re: Setting es:bp
In case anyone was wandering, I've still not solved this problem.

Open to any suggestions.

Cheers,

_________________
Andy Esser
neogenix Broadcast


Sat Nov 14, 2009 12:19 pm
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