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time.pas
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Pascal/Delphi Source File
|
1993-04-19
|
4KB
|
78 lines
UNIT Time; { Copyright (c) 1989-1993 Norbert Juffa }
INTERFACE
FUNCTION Clock: LONGINT; { same as VMS; time in milliseconds }
IMPLEMENTATION
FUNCTION Clock: LONGINT; ASSEMBLER;
ASM
PUSH DS { save caller's data segment }
MOV AX, 0040h { set DS to BIOS data segment to }
MOV DS, AX { access ticker counter }
MOV BX, 6Ch { offset of ticker counter in segm.}
MOV DX, 43h { timer chip control port }
MOV AL, 4 { freeze timer 0 }
PUSHF { save caller's int flag setting }
CLI { make reading counter an atomic operation}
MOV DI, DS:[BX] { read BIOS ticker counter lo word }
MOV CX, DS:[BX+2] { read BIOS ticker counter hi word }
STI { enable update of ticker counter }
OUT DX, AL { latch timer 0 }
NOP { wait for }
NOP { possible ticker }
NOP { counter update }
NOP { interrupt }
NOP { to arrive }
CLI { make reading counter an atomic operation}
MOV SI, DS:[BX] { read BIOS ticker counter lo word }
MOV BX, DS:[BX+2] { read BIOS ticker counter hi word }
IN AL, 40h { read latched timer 0 lo-byte }
MOV AH, AL { save lo-byte }
IN AL, 40h { read latched timer 0 hi-byte }
POPF { restore caller's int flag }
XCHG AL, AH { correct order of hi and lo }
CMP DI, SI { ticker counter updated ? }
JE @no_update { no }
OR AX, AX { update before timer freeze ? }
JNS @no_update { no }
MOV DI, SI { use second }
MOV CX, BX { ticker counter }
@no_update: NOT AX { counter counts down }
MOV BX, 36EDh { load multiplier }
MUL BX { W1 * M }
MOV SI, DX { save W1 * M (hi) }
MOV AX, BX { get M }
MUL DI { W2 * M }
XCHG BX, AX { AX = M, BX = W2 * M (lo) }
MOV DI, DX { DI = W2 * M (hi) }
ADD BX, SI { accumulate }
ADC DI, 0 { result }
XOR SI, SI { load zero }
MUL CX { W3 * M }
ADD AX, DI { accumulate }
ADC DX, SI { result in DX:AX:BX }
MOV DH, DL { move result }
MOV DL, AH { from DL:AX:BX }
MOV AH, AL { to }
MOV AL, BH { DX:AX:BH }
MOV DI, DX { save result }
MOV CX, AX { in DI:CX }
MOV AX, 25110 { calculate correction }
MUL DX { factor }
SUB CX, DX { subtract correction }
SBB DI, SI { factor }
XCHG AX, CX { result back }
MOV DX, DI { to DX:AX }
POP DS { restore caller's data segment }
END;
BEGIN
Port [$43] := $34; { need rate generator, not square wave }
Port [$40] := 0; { generator as programmed by some BIOSes }
Port [$40] := 0; { for timer 0 }
END. { Time }