timer.asm

一个小型的操作系统,采用gcc进行开发,几千行的代码,方便初学者学习

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;
; Snixos Project version 1.0, 2003.6
; (C) Copyright 2003,2004,2005 Jockeyson,KeqiangGao <[e-mail]>
; All Rights Reserved.
; Distributed under the terms of the GNU General Public License.
;
; This program is a free and open source software and you can redistribute 
; it and/or modify it under the terms of the GNU General Public License as
; published by the Free Software Foundation. As no any liability is assumed 
; for any incidental or consequential damages in connection with the 
; information or program fragments contained herein,so any exception arised
; is at your own risk. It is ABSOLUTELY WITHOUT ANY WARRANTY.
; Bug report please send to [e-mail] .
;
;  timer.asm : Programmable Interval Timer 8253 code for Snixos Project
;  Author  : [e-mail]
;  Time    : 2003.6
;
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bits 32
global setPITspeed, delayMS
extern tickcount

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; setPITspeed
; 	Set's the PIT Frequemcy, you'll get a timer interrupt 
;	Hz times per second.  
; args: Push the frequency in Hz on to the stack
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setPITspeed:
	push ebp
	mov ebp,esp
	push eax
	push ebx
	push edx
	xor edx, edx
	mov eax, 0x1234DC		; PIT Frequency
	mov ebx, [esp+20]
	div ebx			        ; Our frequency
	mov ebx, eax			; Save frequency
	xor eax, eax
	mov al, 0x36			; Command word
	out 0x43, al		
	mov ax, bx
	out 0x40, al			; New Frequency
	mov al, ah
	out 0x40, al
	pop edx
	pop ebx
	pop eax
	leave
	ret 
; End setPITspeed

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; delayMS
; 	void delayMS( int duration)
; args: Push the amount of MS you want to delay on the stack
; to call in C: delayMS(100)
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delayMS:
	push ebp
	mov ebp,esp
	push eax
	push ebx
	push ecx
	mov eax, [tickcount]		; Get Current tickcount
	mov ecx, 1
	mul ecx				; Mul 10 to get ms
	mov ecx, [esp+20]		; Get arg
.continue:
	push eax			; Save the prvious tickcount
	mov eax, [tickcount]		; Get current tickcount
	mov ebx, 1
	mul ebx				; Mul 10 to get ms
	mov ebx, eax
	pop eax				; Restore eax
	sub ebx, eax			; Subtract earlier value
	cmp ebx, ecx			; Are they equal yet?
	jb .continue			; Nope, one more time
	pop ecx
	pop eax
	pop ebx
	leave
	ret 
; end of delayMS