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172 lines
3.8 KiB
ArmAsm
172 lines
3.8 KiB
ArmAsm
; timer routines
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; this implementation is for Atari and C64.
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; it uses parts of the C runtime library
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;
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; the timer should be a 16-bit counter that's incremented by about
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; 1000 units per second. it doesn't have to be particularly accurate.
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.include "../inc/common.inc"
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.export timer_init
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.export timer_read
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.export timer_seconds
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.import __clocks_per_sec, _clock
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.import tosumodeax, tosudiveax
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.import pusheax, incsp4
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.importzp sp, sreg
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.bss
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timer_freq: .res 1 ; VBLANK frequency: 50 - PAL, 60 - NTSC (Atari); always 60 (C64)
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mult_temp: .res 2 ; temp var for multiplication routines
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mult_temp_x:.res 1 ; another temp var for multiplication routines
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.data
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mult: .byte $4C ; JMP opcode
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.res 2 ; address
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.code
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; get timer frequency and patch multiplication routine pointer
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; inputs: none
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; outputs: none
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timer_init:
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jsr __clocks_per_sec
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sta timer_freq
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cmp #50
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beq @timer50
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lda #<mult17
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ldx #>mult17
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bne @timerset ; jmp always
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@timer50:
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lda #<mult20
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ldx #>mult20
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@timerset:
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sta mult+1
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stx mult+2
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rts
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; read the current timer value
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; inputs: none
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; outputs: AX = current timer value in milliseconds
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timer_read = mult
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; get current seconds clock hand
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; inputs: none
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; outputs: A = seconds hand (in BCD, range $00..$59)
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timer_seconds:
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jsr _clock ; return current tick count in sreg:AX (high:low 16bits)
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jsr pusheax ; push tick count onto stack
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ldx #0
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stx sreg
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stx sreg+1
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lda timer_freq
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jsr tosudiveax ; dividend on stack, divisor in sreg:AX
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jsr pusheax
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ldx #0
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stx sreg
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stx sreg+1
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lda #60
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jsr tosumodeax ; result modulo 60
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; convert to BCD, a poor man's conversion here....
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cmp #50
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bcs @rs_50
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cmp #40
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bcs @rs_40
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cmp #30
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bcs @rs_30
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cmp #20
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bcs @rs_20
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cmp #10
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bcs @rs_10
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rts
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@rs_10:
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sbc #10
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ora #$10
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rts
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@rs_20:
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sbc #20
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ora #$20
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rts
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@rs_30:
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sbc #30
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ora #$30
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rts
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@rs_40:
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sbc #40
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ora #$40
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rts
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@rs_50:
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sbc #50
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ora #$50
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rts
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; get the current tick count, multiply it by 20, and return the lower 16 bits
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; x*20 = x*16 + x*4
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; inputs: none
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; outputs: AX - tick count times 20 ('milliseconds')
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mult20:
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jsr _clock ; return current tick count in sreg:AX (high:low 16bits)
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stx mult_temp_x ; remember high byte of lower 16bits
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asl a
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rol mult_temp_x
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asl a
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rol mult_temp_x
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sta mult_temp
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ldx mult_temp_x
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stx mult_temp+1 ; mult_temp = ticks * 4
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asl a
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rol mult_temp_x
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asl a
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rol mult_temp_x ; mult_temp_x:A = 'ticks * 16'
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clc ; AX - tick count * 16, mult_temp - tick count * 4
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adc mult_temp
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sta mult_temp
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lda mult_temp+1
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adc mult_temp_x
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tax
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lda mult_temp
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rts
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; get the current tick count, multiply it by 17, and return the lower 16 bits
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; x*17 = x*16 + x
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; inputs: none
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; outputs: AX - tick count times 17 ('milliseconds')
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mult17:
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jsr _clock ; return current tick count in sreg:AX (high:low 16bits)
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sta mult_temp
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stx mult_temp+1
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stx mult_temp_x
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.repeat 4
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asl a
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rol mult_temp_x
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.endrepeat ; mult_temp_x:A = 'ticks * 16'
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clc
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adc mult_temp
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sta mult_temp
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lda mult_temp+1
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adc mult_temp_x
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tax
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lda mult_temp
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rts
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;-- LICENSE FOR clk_timer.s --
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; The contents of this file are subject to the Mozilla Public License
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; Version 1.1 (the "License"); you may not use this file except in
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; compliance with the License. You may obtain a copy of the License at
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; http://www.mozilla.org/MPL/
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;
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; Software distributed under the License is distributed on an "AS IS"
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; basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
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; License for the specific language governing rights and limitations
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; under the License.
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; -- LICENSE END --
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