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irq.inc
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;*******************************************************************************
;Copyright 2022-2024, Stefan Jakobsson
;
;Redistribution and use in source and binary forms, with or without modification,
;are permitted provided that the following conditions are met:
;
;1. Redistributions of source code must retain the above copyright notice, this
; list of conditions and the following disclaimer.
;
;2. Redistributions in binary form must reproduce the above copyright notice,
; this list of conditions and the following disclaimer in the documentation
; and/or other materials provided with the distribution.
;
;THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS”
;AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
;IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
;DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
;FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
;DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
;SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
;CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
;OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
;OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
;*******************************************************************************
;******************************************************************************
;Function name.......: irq_init
;Purpose.............: Initializes the custom interrupt handler
;Input...............: None
;Returns.............: Nothing
;Error returns.......: None
.if target_mem=target_ram
.proc irq_init
;Backup default interrupt handler
lda $0314
sta irq_default_handler
lda $0315
sta irq_default_handler+1
;Set vectors to our custom handler
sei
stz irq_flag
lda #<irq_handler
sta $0314
lda #>irq_handler
sta $0315
cli
rts
.endproc
.endif
.if target_mem=target_rom
.proc irq_init
;Backup default interrupt handler
lda $0314
sta irq_default_handler
lda $0315
sta irq_default_handler+1
;Set vectors to our custom handler
sei
lda #<(bridge_code+bridge_irq-bridge_kernal)
sta $0314
lda #>(bridge_code+bridge_irq-bridge_kernal)
sta $0315
cli
rts
.endproc
.endif
;******************************************************************************
;Function name.......: irq_restore
;Purpose.............: Restores original IRQ handler
;Input...............: None
;Returns.............: Nothing
;Error returns.......: None
.proc irq_restore
sei
lda irq_default_handler
sta $0314
lda irq_default_handler+1
sta $0315
cli
rts
.endproc
;******************************************************************************
;Function name.......: irq_handler
;Purpose.............: Custom interrupt handler
;Input...............: None
;Returns.............: Nothing
;Error returns.......: None
.proc irq_handler
;Verify vblank interrupt
lda VERA_ISR
and #$01
beq exit
;Set IRQ flag
lda #1
sta irq_flag
exit:
.if (::target_mem=target_ram)
jmp (irq_default_handler)
.endif
.if (::target_mem=target_rom)
rts
.endif
.endproc
.segment "VARS"
irq_default_handler: .res 2 ;2 bytes
irq_flag: .res 1
.CODE