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-rw-r--r--core/timer.inc15
1 files changed, 13 insertions, 2 deletions
diff --git a/core/timer.inc b/core/timer.inc
index 728812b1..b01ff917 100644
--- a/core/timer.inc
+++ b/core/timer.inc
@@ -19,6 +19,9 @@
;; 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
@@ -35,12 +38,20 @@ timer_cleanup:
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
-__jiffies dd 0 ; The actual timer variable
+ 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