need some help with VGA (bios interrupts)

[Pyrofan1]

video.s

Code: Select all

.globl _init_graphics
.globl _init_text

.type _init_graphics,@function
_init_graphics:
    mov $0x00, %ah
    mov $0x13, %al
    int $0x10

.type _init_text,@function
_init_text:
    mov $0x00, %ah
    mov $0x03, %al
    int $0x10

when I try to use any of these functions it causes the computer to reboot, but I don't know why.

[Brynet-Inc]

video.s

Code: Select all

.globl _init_graphics
.globl _init_text

.type _init_graphics,@function
_init_graphics:
    mov $0x00, %ah
    mov $0x13, %al
    int $0x10

.type _init_text,@function
_init_text:
    mov $0x00, %ah
    mov $0x03, %al
    int $0x10

when I try to use any of these functions it causes the computer to reboot, but I don't know why.

You really should "clarify" more about your OS, We are not physic buddy lol..

I'll give hints:
1) You cannot use BIOS interrupts in protected mode...
2) GAS requires that .code16 be used when generating realmode code..

I hope this helps in some way.. I also found an example on creating a boot sector program using GAS.
http://www.cs.usfca.edu/~cruse/cs630f06/ldscript
http://www.cs.usfca.edu/~cruse/cs630f06/memsize.s

(Most of the BSD's use GAS for this purpose as well...)

Have fun

[Pyrofan1]

You really should "clarify"

What should I clarify?

[Brynet-Inc]

You really should "clarify"

What should I clarify?

...Was that follow up post really necessary? I clearly stated that in my initial post.

Anyway, It doesn't matter now.. I hope I helped some..

[Pyrofan1]

I hope I helped some..

you didn't, I already knew that I need to be in real mode and I already has .code16 in my code

[Kevin McGuire]

video.s

Code: Select all

.globl _init_graphics
.globl _init_text

.type _init_graphics,@function
_init_graphics:
    mov $0x00, %ah
    mov $0x13, %al
    int $0x10

.type _init_text,@function
_init_text:
    mov $0x00, %ah
    mov $0x03, %al
    int $0x10

when I try to use any of these functions it causes the computer to reboot, but I don't know why.

A Slightly Better Question, But Not Real Good One Since I Do Not Ask Questions Much

I am using a real computer to boot my kernel with GRUB into protected mode. I am calling these assembler function from C by:

Code: Select all

init_graphics();
init_text();

I have created and loaded the: IDT and GDT. There are no exceptions or interrupts before the computer reboots. My stack is located at 0x100000, the current ESP was 0x100087 before I made the calls. My kernel is loaded at 0x1400000. I have also tried my kernel in a emulator such as BOCHS and QEMU with the same problem (reboot).

I have inserted test code to ensure that the functions are being called correctly, and that the problem is after the interrupt instruction. I have put BOCHS into debug mode and stepped through the function call to also verify that the problem happens after the interrupt instruction... but there are so many instructions afterwards that I can never step through all of them to find exactly where the problem happens.

I have also tested my IDT by causing a "divide by zero" exception, and issued software interrupts also with success. I have tested my GDT with a long jump and changing the DS and SS segments with success (and issuing memory accesses with the DS and SS segments).

[urxae]

Try putting a "ret" at the end of each of those functions...

[Pyrofan1]

GRUB into protected mode

Wait, GRUB boot into protected mode?

[urxae]

GRUB into protected mode

Wait, GRUB boot into protected mode?

If you're using it as a multiboot bootloader, yes. If you're using it as a chainloader, no. I'm not sure about the other boot protocols it supports ("Linux zImage or bzImage, FreeBSD a.out, NetBSD a.out, etc.", according to the manual).

GRUB supports a few boot protocols . Multiboot is the preferred one though, the rest is mostly for (backward?) compatibility IIRC (so it would actually be useful without requiring everyone to switch to Multiboot).

[Pyrofan1]

Then how do I switch to real mode?

[Brynet-Inc]

Then how do I switch to real mode?

1) Load the segment registers with real-mode compatible values..
2) Reset the Protection Enable (PE) bit in CR0..
3) Load the segment registers with real mode values..
4) Inhibit A20 from the address bus (gate A20 off)..

Note that leaving protected mode requires loading the segment registers twice..

The segment registers are loaded the first time to assure that real-mode compatible values are stored in the hidden descriptor cache registers -- as the descriptor cache registers "honour" the access attributes, and segment size limit, from protected mode, even when loaded in real mode. The segment registers are loaded the second time to define them with real-mode segment values.

[Combuster]

@Brynet: You forgot the details

@Pyrofan1: Don't bother with the segment limit and A20. There isn't any reason why you should. That brynet-inc is a purist doesnt mean you are not allowed to make your life easier by running unreal mode instead. Also, the BIOS should be sensible enough to not depend on one specific A20 setting. More so for the VGA bios

- you'd need to set up a GDT with both 32 and 16 bit code+data segments
- then you'd need to reload cs to enter 16 bit protected mode. You need a far jump for this. Since GRUB won't allow loading to <1M you have to copy code to the realmode area yourself.
- then you need to clear PE
- then you need to reload CS again so that it holds a real-mode value.
- reload the remaining segment registers. This'll mean you end up in unreal mode, but since that doesnt change anything from the bios' perspective, why bother.
- you might as well enable interrupts by now

now you can call bios interrupts

then,
- disable interrupts
- set PE bit again
- flush cs and jump back to 32-bit code
- reload the remaining segments registers

You might want to consider asking GRUB to set a mode for you instead (see documentation), or postpone changing modes to a later stage when you can run Virtual 8086 tasks. Graphics mode is hardly a prerequisite for a functional system.