dos33fsprogs/pt3_player/interrupt_handler.s

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;================================
;================================
; mockingboard interrupt handler
;================================
;================================
; On Apple II/6502 the interrupt handler jumps to address in 0xfffe
; This is in the ROM, which saves the registers
; on older IIe it saved A to $45 (which could mess with DISK II)
; newer IIe doesn't do that.
; It then calculates if it is a BRK or not (which trashes A)
; Then it sets up the stack like an interrupt and calls 0x3fe
; Note: the IIc is much more complicated
; its firmware tries to decode the proper source
; based on various things, including screen hole values
; we bypass that by switching out ROM and replacing the
; $fffe vector with this, but that does mean we have
; to be sure status flag and accumulator set properly
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TIME_OFFSET = 13
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interrupt_handler:
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php
pha ; save A ; 3
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; A is saved in $45 by firmware
txa
pha ; save X
tya
pha ; save Y
; inc $0404 ; debug (flashes char onscreen)
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.include "pt3_lib_irq_handler.s"
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;==============================================
; only update time counter if not done playing
;==============================================
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lda DONE_PLAYING ; 3
bne check_keyboard
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;=====================
; Update time counter
;=====================
; self-modifying version via qkumba
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update_time:
inc frame_count_smc+1 ; 5
frame_count_smc:
lda #$0 ; 2
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eor #50 ; 3
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bne done_time ; 3/2nt
sta frame_count_smc+1 ; 3
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ldx $7d0+TIME_OFFSET+3 ; 4
cpx #'9'+$80 ; 2
bne update_second_ones ; 3/2nt
ldx $7d0+TIME_OFFSET+2 ; 4
cpx #'5'+$80 ; 6-1 (for 60 seconds) ; 2
bne update_second_tens ; 3/2nt
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update_minutes:
inc $7d0+TIME_OFFSET ; 6
inc $bd0+TIME_OFFSET ; 6
ldx #'0'+$80-1 ; 2
update_second_tens:
inx ; 2
stx $7d0+TIME_OFFSET+2 ; 4
stx $bd0+TIME_OFFSET+2 ; 4
ldx #'0'+$80-1 ; 2
update_second_ones:
inx ; 2
stx $7d0+TIME_OFFSET+3 ; 4
stx $bd0+TIME_OFFSET+3 ; 4
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; we don't handle > 9:59 songs yet
done_time:
;=============
; 52 worst
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;=================================
; Handle keyboard
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;=================================
check_keyboard:
jsr get_key
tax
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beq exit_interrupt
;====================
; space pauses
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cmp #(' '+$80) ; set carry if true
bne key_M
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key_space:
lda #$80
eor DONE_PLAYING
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; disable fire when paused
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sta DONE_PLAYING
beq yes_bar
lda #0
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beq lowbar ; branch always
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yes_bar:
lda #7
lowbar:
jsr fire_setline
ldx DONE_PLAYING
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bcs quiet_exit ; branch always
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;===========================
; M key switches MHz mode
key_M:
cmp #'M'
bne key_L ; set carry if true
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ldx #'0'+$80
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lda convert_177_smc1
eor #$20
sta convert_177_smc1
sta convert_177_smc2
sta convert_177_smc3
sta convert_177_smc4
sta convert_177_smc5
cmp #$18
beq at_MHz
; update text on screen
ldx #'7'+$80
at_MHz:
stx $7F4
stx $BF4
bcs done_key ; branch always
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;===========================
; L enables loop mode
key_L:
cmp #'L'
bne key_left ; set carry if true
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ldx #'/'+$80
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lda LOOP
eor #$1
sta LOOP
beq music_looping
; update text on screen
ldx #'L'+$80
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music_looping:
stx $7D0+18
stx $BD0+18
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bcs done_key ; branch always
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;======================
; left key, to prev song
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key_left:
ldx #$40
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cmp #'A'
beq quiet_exit
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;========================
; right key, to next song
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key_right:
ldx #$20
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cmp #'D'
bne done_key
;========================
; stop playing for now
; quiet down the Mockingboard
; (otherwise will be stuck on last note)
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quiet_exit:
stx DONE_PLAYING
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jsr clear_ay_both
;ldx #$ff ; also mute the channel
stx AY_REGISTERS+7 ; just in case
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done_key:
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exit_interrupt:
pla
tay ; restore Y
pla
tax ; restore X
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pla ; restore a ; 4
; this is needed on II+/IIe not not IIc
interrupt_smc:
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lda $45 ; restore A
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plp
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rti ; return from interrupt ; 6
;============
; typical
; ???? cycles