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;; -----------------------------------------------------------------------
;;
;; Copyright 2009 Intel Corporation; author: H. Peter Anvin
;;
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
;; Boston MA 02110-1301, USA; either version 2 of the License, or
;; (at your option) any later version; incorporated herein by reference.
;;
;; -----------------------------------------------------------------------
;;
;; timer.inc
;;
;; Very simple counting timer
;;
;; This lets us have a simple incrementing variable without worrying
;; about the BIOS_timer variable wrapping around at "midnight" and other
;; weird things.
;;
;; This also maintains a timer variable calibrated in milliseconds
;; (wraparound time = 49.7 days!)
;;
section .text16
timer_init:
; Hook INT 1Ch
mov eax,[BIOS_timer_hook]
mov [BIOS_timer_next],eax
mov dword [BIOS_timer_hook],timer_irq
ret
timer_cleanup:
; Unhook INT 1Ch
mov eax,[BIOS_timer_next]
mov [BIOS_timer_hook],eax
ret
;
; The specified frequency is 14.31818 MHz/12/65536; this turns out
; to be a period of 54.92542 ms, or 0x36.ece8(187c) hexadecimal.
;
timer_irq:
inc dword [cs:__jiffies]
add word [cs:__ms_timer_adj],0xece8
adc dword [cs:__ms_timer],0x36
jmp 0:0
BIOS_timer_next equ $-4
section .data16
alignz 4
global __jiffies, __ms_timer
__jiffies dd 0 ; Clock tick timer
__ms_timer dd 0 ; Millisecond timer
__ms_timer_adj dw 0 ; Millisecond timer correction factor
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