mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-11-18 06:09:08 +00:00
70 lines
1.6 KiB
ArmAsm
70 lines
1.6 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:
|
|
php ; save status flags
|
|
cld ; clear decimal mode
|
|
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:
|
|
|
|
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
|
|
|