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Diffstat (limited to 'contrib/syslinux-4.02/core/timer.inc')
| -rw-r--r-- | contrib/syslinux-4.02/core/timer.inc | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/contrib/syslinux-4.02/core/timer.inc b/contrib/syslinux-4.02/core/timer.inc new file mode 100644 index 0000000..b01ff91 --- /dev/null +++ b/contrib/syslinux-4.02/core/timer.inc @@ -0,0 +1,57 @@ +;; ----------------------------------------------------------------------- +;; +;; 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 |