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| author | H. Peter Anvin <hpa@zytor.com> | 2009-09-02 17:44:32 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2009-09-02 17:44:32 -0700 |
| commit | 75d4dec2f651c9f25fa95d6b6960db7c4dcfd7a0 (patch) | |
| tree | 1fc477d5f43577a31eaaff7c5a17f719c4e69e1d /core/timer.inc | |
| parent | 94a6e382a7a253fdab67a3bff981844dd5f6d4cb (diff) | |
| download | syslinux-75d4dec2f651c9f25fa95d6b6960db7c4dcfd7a0.tar.gz | |
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@zytor.com>
Diffstat (limited to 'core/timer.inc')
| -rw-r--r-- | core/timer.inc | 45 |
1 files changed, 45 insertions, 0 deletions
diff --git a/core/timer.inc b/core/timer.inc new file mode 100644 index 00000000..caae8265 --- /dev/null +++ b/core/timer.inc @@ -0,0 +1,45 @@ +;; ----------------------------------------------------------------------- +;; +;; 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. +;; + + 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 + +timer_irq: + inc dword [cs:__jiffies] + jmp 0:0 +BIOS_timer_next equ $-4 + + section .bss16 + global __jiffies +__jiffies resd 1 ; The actual timer variable |