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Revision 75d4dec2f651c9f25fa95d6b6960db7c4dcfd7a0, 1.2 KB
(checked in by H. Peter Anvin <hpa@…>, 3 years ago)
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core: hook INT 1Ch for a simple monotonic timer
The BIOS_timer variable at 4C6h is somewhat unreliable... it is
documented to wrap at "midnight", norminally after 1627419 ticks
(0x18d51b), which is a rather awkward number to deal with modulo.
Instead, hook the INT 1Ch secondary timer interrupt and just count a
simple incrementing variable.
Signed-off-by: H. Peter Anvin <hpa@…>
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| 1 | ;; ----------------------------------------------------------------------- |
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| 2 | ;; |
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| 3 | ;; Copyright 1994-2008 H. Peter Anvin - All Rights Reserved |
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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., 53 Temple Place Ste 330, |
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| 8 | ;; Boston MA 02111-1307, 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 | ;; bios.inc |
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| 15 | ;; |
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| 16 | ;; Header file for the BIOS data structures etc. |
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| 17 | ;; |
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| 18 | |
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| 19 | %ifndef _BIOS_INC |
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| 20 | %define _BIOS_INC |
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| 21 | global BIOS_fbm, BIOS_timer |
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| 22 | |
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| 23 | ; Interrupt vectors |
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| 24 | absolute 4*1Ch |
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| 25 | BIOS_timer_hook resd 1 |
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| 26 | |
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| 27 | absolute 4*1Eh |
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| 28 | fdctab equ $ |
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| 29 | fdctab1 resw 1 |
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| 30 | fdctab2 resw 1 |
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| 31 | |
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| 32 | absolute 0400h |
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| 33 | serial_base resw 4 ; Base addresses for 4 serial ports |
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| 34 | absolute 0413h |
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| 35 | BIOS_fbm resw 1 ; Free Base Memory (kilobytes) |
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| 36 | absolute 0462h |
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| 37 | BIOS_page resb 1 ; Current video page |
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| 38 | absolute 046Ch |
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| 39 | BIOS_timer resw 1 ; Timer ticks |
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| 40 | absolute 0472h |
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| 41 | BIOS_magic resw 1 ; BIOS reset magic |
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| 42 | absolute 0484h |
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| 43 | BIOS_vidrows resb 1 ; Number of screen rows |
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| 44 | |
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| 45 | %endif ; _BIOS_INC |
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