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cc65/libsrc/atari/irq.s
Christian Groessler 1cc4fa9356 Atari: fix interrupt handling if extended memory is banked in
Extendend memory is mapped over the main memory in the 0x4000..0x7FFF
area. Many DOSes disable interrupts while extended memory is banked in,
but not all (e.g. SpartaDOS-X).
This change modifies the initial interrupt handler to map in main memory
before chaining to the "worker" handlers.
Since the initial interrupt handler uses a data segment to store the
trampoline to chain to the original handler, introduce a new "LOWBSS"
segment to hold this trampoline. Otherwise the trampoline may end up
inside the 0x4000..0x7FFF area.

Add a link time warning if "LOWCODE" segment lays within the extended
memory window.
2018-09-05 11:28:15 +02:00

81 lines
1.8 KiB
ArmAsm

;
; IRQ handling (ATARI version)
;
.export initirq, doneirq
.import callirq
.include "atari.inc"
.ifdef __ATARIXL__
.import __CHARGEN_START__
.include "romswitch.inc"
.endif
; ------------------------------------------------------------------------
.segment "ONCE"
initirq:
lda #$4C ; JMP opcode
sta IRQInd
lda VVBLKD
ldx VVBLKD+1
sta IRQInd+1
stx IRQInd+2
lda #7
ldy #<IRQStub
ldx #>IRQStub
jmp SETVBV
; ------------------------------------------------------------------------
.code
doneirq:
lda #7
ldy IRQInd+1
ldx IRQInd+2
jmp SETVBV
; ------------------------------------------------------------------------
.segment "LOWCODE"
IRQStub:
cld ; Just to be sure
.ifdef __ATARIXL__
.ifdef CHARGEN_RELOC
lda CHBAS
pha
.endif
.endif
lda PORTB
pha
.ifdef __ATARIXL__
and #$FE ; disable ROM
.endif
ora #$10 ; map main memory into $4000..$7FFF area
sta PORTB
.ifdef __ATARIXL__
set_chbase >__CHARGEN_START__
.endif
jsr callirq ; Call the functions
pla
sta PORTB ; restore old memory settings
.ifdef __ATARIXL__
.ifdef CHARGEN_RELOC
pla
sta CHBAS
sta CHBASE
.endif
.endif
jmp IRQInd ; Jump to the saved IRQ vector
; ------------------------------------------------------------------------
.segment "LOWBSS"
IRQInd: .res 3
.end