Programmable Interrupt Timer

[cipek]

I don't know how reprogramable PIT to 100Hz frequency. Please help me !!!
I've got this code in C but i don't know how change it into asembly

Code: Select all

void ChangePITfrequency(unsigned long hz)
{
 unsigned long val=1193180/hz;
 outb(0x36,0x43);
 outb(val&0xff,0x40);
 outb((val>>8)&0xff,0x40);
}

[Daidalos]

The "outb function" above is just a macro that emits inline assembly. Translate them directly into OUT assembly language instructions with an 8-bit data operand.

[cipek]

yes i know what is outb. It's asembly out istruction. but i don't know how trenslate it into asembly:

Code: Select all

 outb(val&0xff,0x40);
 outb((val>>8)&0xff,0x40);

[Anton]

I don't know how reprogramable PIT to 100Hz frequency. Please help me !!!
I've got this code in C but i don't know how change it into asembly

Code: Select all

void ChangePITfrequency(unsigned long hz)
{
 unsigned long val=1193180/hz;
 outb(0x36,0x43);
 outb(val&0xff,0x40);
 outb((val>>8)&0xff,0x40);
}

I havent programed in asm for a long time, so i am trying my best:

mov eax,1193180
mov edx,0
div hz;
mov ebx,eax;//saving-it better be 2 bytes!

mov dx,0x43;
mov al,0x36;
out dx,al;

mov dx,0x40;
mov al,bl;
out dx,al;
mov al,bh;
out dx,al;

[chase]

Instead of converting the code to assembly you could also do the assembly inside of the C code with inline assembly. We've got a quick tutorial for doing this type of thing located at http://www.osdev.org/howtos/2/index.html

[rexlunae]

Instead of converting the code to assembly you could also do the assembly inside of the C code with inline assembly. We've got a quick tutorial for doing this type of thing located at http://www.osdev.org/howtos/2/index.html

I agree. It would be much better in most cases to use inline assembly where necessary rather than converting entire functions to assembly. However if you are dead-set on converting the code to assembly, you could just use the -S option to gcc to do it.

gcc -S foo.c

will make a file called foo.s which is the assembly for your file.

[cipek]

Thank's everybody! I do that

Code: Select all

 mov al,0b6h
 out 42h,al
 mov ax,11930
 out 40h,al
 mov al,ah
 out 40h,al
 ret

I don't testing it but i think it's work

[pepito]

I use this code:

mov al, 0x36 ; Couter-0, LSB-MSB, Onda-4, n-Binary
out 0x43, al

mov ax, 11931 ; Divisor for 100MHz
out 0x40, al ; Send LSB
shr ax, 8
out 0x40, al ; Send MSB

[Anton]

shr ax, 8
out 0x40, al ; Send MSB

=
out 0x40,ah
(I think )

[Da_Maestro]

shr ax, 8
out 0x40, al ; Send MSB

=
out 0x40,ah
(I think )

That instruction is an invalid combination of opcodes and operands. The out instruction uses only AL or an immediate operand. It cannot use a memory location or any other registers either.

[dr_watts]

Could always use the Local APIC if you have one...