nesemu/test_roms/cpu_exec_space/source/common/delay.s

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2023-12-03 00:27:07 -05:00
; Delays in CPU clocks, milliseconds, etc. All routines are re-entrant
; (no global data). No routines touch X or Y during execution.
; Code generated by macros is relocatable; it contains no JMPs to itself.
zp_byte delay_temp_ ; only written to
; Delays n clocks, from 2 to 16777215
; Preserved: A, X, Y, flags
.macro delay n
.if (n) < 0 .or (n) = 1 .or (n) > 16777215
.error "Delay out of range"
.endif
delay_ (n)
.endmacro
; Delays n milliseconds (1/1000 second)
; n can range from 0 to 1100.
; Preserved: A, X, Y, flags
.macro delay_msec n
.if (n) < 0 .or (n) > 1100
.error "time out of range"
.endif
delay ((n)*CLOCK_RATE+500)/1000
.endmacro
; Delays n microseconds (1/1000000 second).
; n can range from 0 to 100000.
; Preserved: A, X, Y, flags
.macro delay_usec n
.if (n) < 0 .or (n) > 100000
.error "time out of range"
.endif
delay ((n)*((CLOCK_RATE+50)/100)+5000)/10000
.endmacro
.align 64
; Delays A clocks + overhead
; Preserved: X, Y
; Time: A+25 clocks (including JSR)
: sbc #7 ; carry set by CMP
delay_a_25_clocks:
cmp #7
bcs :- ; do multiples of 7
lsr a ; bit 0
bcs :+
: ; A=clocks/2, either 0,1,2,3
beq @zero ; 0: 5
lsr a
beq :+ ; 1: 7
bcc :+ ; 2: 9
@zero: bne :+ ; 3: 11
: rts ; (thanks to dclxvi for the algorithm)
; Delays A*256 clocks + overhead
; Preserved: X, Y
; Time: A*256+16 clocks (including JSR)
delay_256a_16_clocks:
cmp #0
bne :+
rts
delay_256a_11_clocks_:
: pha
lda #256-19-22
jsr delay_a_25_clocks
pla
clc
adc #-1&$FF
bne :-
rts
; Delays A*65536 clocks + overhead
; Preserved: X, Y
; Time: A*65536+16 clocks (including JSR)
delay_65536a_16_clocks:
cmp #0
bne :+
rts
delay_65536a_11_clocks_:
: pha
lda #256-19-22-13
jsr delay_a_25_clocks
lda #255
jsr delay_256a_11_clocks_
pla
clc
adc #-1&$FF
bne :-
rts
max_short_delay = 41
; delay_short_ macro jumps into these
.res (max_short_delay-12)/2,$EA ; NOP
delay_unrolled_:
rts
.macro delay_short_ n
.if n < 0 .or n = 1 .or n > max_short_delay
.error "Internal delay error"
.endif
.if n = 0
; nothing
.elseif n = 2
nop
.elseif n = 3
sta <delay_temp_
.elseif n = 4
nop
nop
.elseif n = 5
sta <delay_temp_
nop
.elseif n = 6
nop
nop
nop
.elseif n = 7
php
plp
.elseif n = 8
nop
nop
nop
nop
.elseif n = 9
php
plp
nop
.elseif n = 10
sta <delay_temp_
php
plp
.elseif n = 11
php
plp
nop
nop
.elseif n = 13
php
plp
nop
nop
nop
.elseif n & 1
sta <delay_temp_
jsr delay_unrolled_-((n-15)/2)
.else
jsr delay_unrolled_-((n-12)/2)
.endif
.endmacro
.macro delay_nosave_ n
; 65536+17 = maximum delay using delay_256a_11_clocks_
; 255+27 = maximum delay using delay_a_25_clocks
; 27 = minimum delay using delay_a_25_clocks
.if n > 65536+17
lda #^(n - 15)
jsr delay_65536a_11_clocks_
; +2 ensures remaining clocks is never 1
delay_nosave_ (((n - 15) & $FFFF) + 2)
.elseif n > 255+27
lda #>(n - 15)
jsr delay_256a_11_clocks_
; +2 ensures remaining clocks is never 1
delay_nosave_ (<(n - 15) + 2)
.elseif n >= 27
lda #<(n - 27)
jsr delay_a_25_clocks
.else
delay_short_ n
.endif
.endmacro
.macro delay_ n
.if n > max_short_delay
php
pha
delay_nosave_ (n - 14)
pla
plp
.else
delay_short_ n
.endif
.endmacro