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