f5dbe46060
irq_set_status can be used to clear the irq status bit so that the interrupt will stop occuring.
58 lines
2.0 KiB
ArmAsm
58 lines
2.0 KiB
ArmAsm
; ---------------------------------------------------------------------------
|
|
; interrupt.s
|
|
; ---------------------------------------------------------------------------
|
|
;
|
|
; Interrupt handler.
|
|
;
|
|
; Checks for a BRK instruction and returns from all valid interrupts.
|
|
|
|
.import _handle_irq
|
|
|
|
.export _irq_int, _nmi_int
|
|
.export _irq_get_status, _irq_set_status
|
|
|
|
.include "io.inc65"
|
|
|
|
.segment "CODE"
|
|
|
|
.PC02 ; Force 65C02 assembly mode
|
|
|
|
; ---------------------------------------------------------------------------
|
|
; Non-maskable interrupt (NMI) service routine
|
|
|
|
_nmi_int: RTI ; Return from all NMI interrupts
|
|
|
|
; ---------------------------------------------------------------------------
|
|
; Maskable interrupt (IRQ) service routine
|
|
|
|
_irq_int: PHX ; Save X register contents to stack
|
|
TSX ; Transfer stack pointer to X
|
|
PHA ; Save accumulator contents to stack
|
|
INX ; Increment X so it points to the status
|
|
INX ; register value saved on the stack
|
|
LDA $100,X ; Load status register contents
|
|
AND #$10 ; Isolate B status bit
|
|
BNE break ; If B = 1, BRK detected
|
|
|
|
; ---------------------------------------------------------------------------
|
|
; IRQ detected, return
|
|
|
|
irq: PLA ; Restore accumulator contents
|
|
PLX ; Restore X register contents
|
|
jsr _handle_irq ; Handle the IRQ
|
|
RTI ; Return from all IRQ interrupts
|
|
|
|
; ---------------------------------------------------------------------------
|
|
; BRK detected, stop
|
|
|
|
break: JMP break ; If BRK is detected, something very bad
|
|
; has happened, so stop running
|
|
|
|
_irq_get_status:
|
|
lda IRQ_STATUS
|
|
ldx #$00
|
|
rts
|
|
|
|
_irq_set_status:
|
|
sta IRQ_STATUS
|
|
rts |