dos33fsprogs/demos/logo_demo/interrupt_handler.s
2021-11-07 23:31:56 -05:00

159 lines
2.6 KiB
ArmAsm

;================================
;================================
; 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
interrupt_handler:
cld ; must be first in ProDOS handler
; no need to save, ProDOS does it for us?
; php ; save status flags
; pha ; save A ; 3
; A is saved in $45 by firmware
; txa
; pha ; save X
; tya
; pha ; save Y
; inc $0404 ; debug (flashes char onscreen)
.include "pt3_lib_irq_handler.s"
jmp exit_interrupt
;=================================
; Finally done with this interrupt
;=================================
quiet_exit:
stx DONE_PLAYING
jsr clear_ay_both
ldx #$ff ; also mute the channel
stx AY_REGISTERS+7 ; just in case
exit_interrupt:
; update time
; inc ticks
; lda ticks
; cmp #50
; bne no_tick_oflo
; lda #0
; sta ticks
; inc seconds
no_tick_oflo:
; if done, no timeout
; lda command
; cmp #DONE
; beq handle_credits
; trigger at timeout value
; lda seconds
; cmp timeout
; bne handle_credits
; inc trigger
; lda which
; asl
; tax
; lda todo_list,x
; sta command
; cmp #DO_CREDITS
; bne itsnot
; jsr switch_to_credits
; lda command
itsnot:
; cmp #DONE
; beq handle_credits
; lda todo_list+1,x
; sta timeout
; point to next
; inc which
; reset seconds
; lda #0
; sta seconds
; HUGE HACK
; return to our code instead of BASIC
; ldx original_stack
; txs
; lda #>command_loop
; pha
; lda #<command_loop
; pha
; lda #0 ; program status word
; pha
; rti
;handle_credits:
; lda command
; cmp #DONE
; bne done_match
; jsr display_credits
done_match:
clc ; tell ProDOS we handled things
rts ; ProDOS handles rti?
; pla
; tay ; restore Y
; pla
; tax ; restore X
; pla ; restore a ; 4
; on II+/IIe (but not IIc) we need to do this?
interrupt_smc:
; lda $45 ; restore A
; plp
; rti ; return from interrupt ; 6
;============
; typical
; ???? cycles
seconds: .byte $00
ticks: .byte $00