| 1 | ;; ----------------------------------------------------------------------- |
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| 2 | ;; |
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| 3 | ;; Copyright 2009 Intel Corporation; author: H. Peter Anvin |
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| 4 | ;; |
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| 5 | ;; This program is free software; you can redistribute it and/or modify |
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| 6 | ;; it under the terms of the GNU General Public License as published by |
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| 7 | ;; the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, |
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| 8 | ;; Boston MA 02110-1301, USA; either version 2 of the License, or |
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| 9 | ;; (at your option) any later version; incorporated herein by reference. |
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| 10 | ;; |
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| 11 | ;; ----------------------------------------------------------------------- |
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| 12 | |
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| 13 | ;; |
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| 14 | ;; timer.inc |
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| 15 | ;; |
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| 16 | ;; Very simple counting timer |
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| 17 | ;; |
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| 18 | ;; This lets us have a simple incrementing variable without worrying |
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| 19 | ;; about the BIOS_timer variable wrapping around at "midnight" and other |
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| 20 | ;; weird things. |
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| 21 | ;; |
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| 22 | ;; This also maintains a timer variable calibrated in milliseconds |
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| 23 | ;; (wraparound time = 49.7 days!) |
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| 24 | ;; |
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| 25 | |
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| 26 | section .text16 |
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| 27 | |
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| 28 | timer_init: |
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| 29 | ; Hook INT 1Ch |
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| 30 | mov eax,[BIOS_timer_hook] |
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| 31 | mov [BIOS_timer_next],eax |
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| 32 | mov dword [BIOS_timer_hook],timer_irq |
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| 33 | ret |
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| 34 | |
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| 35 | global bios_timer_cleanup:function hidden |
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| 36 | bios_timer_cleanup: |
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| 37 | ; Unhook INT 1Ch |
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| 38 | mov eax,[BIOS_timer_next] |
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| 39 | mov [BIOS_timer_hook],eax |
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| 40 | ret |
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| 41 | |
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| 42 | ; |
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| 43 | ; The specified frequency is 14.31818 MHz/12/65536; this turns out |
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| 44 | ; to be a period of 54.92542 ms, or 0x36.ece8(187c) hexadecimal. |
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| 45 | ; |
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| 46 | global timer_irq:function hidden |
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| 47 | timer_irq: |
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| 48 | inc dword [cs:__jiffies] |
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| 49 | add word [cs:__ms_timer_adj],0xece8 |
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| 50 | adc dword [cs:__ms_timer],0x36 |
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| 51 | jmp 0:0 |
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| 52 | global BIOS_timer_next:data hidden |
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| 53 | BIOS_timer_next equ $-4 |
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| 54 | |
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| 55 | section .data16 |
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| 56 | alignz 4 |
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| 57 | global __jiffies:data hidden, __ms_timer |
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| 58 | __jiffies dd 0 ; Clock tick timer |
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| 59 | __ms_timer dd 0 ; Millisecond timer |
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| 60 | __ms_timer_adj dw 0 ; Millisecond timer correction factor |
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