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1cc4fa9356
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.
81 lines
1.8 KiB
ArmAsm
81 lines
1.8 KiB
ArmAsm
;
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; IRQ handling (ATARI version)
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;
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.export initirq, doneirq
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.import callirq
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.include "atari.inc"
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.ifdef __ATARIXL__
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.import __CHARGEN_START__
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.include "romswitch.inc"
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.endif
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; ------------------------------------------------------------------------
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.segment "ONCE"
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initirq:
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lda #$4C ; JMP opcode
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sta IRQInd
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lda VVBLKD
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ldx VVBLKD+1
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sta IRQInd+1
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stx IRQInd+2
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lda #7
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ldy #<IRQStub
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ldx #>IRQStub
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jmp SETVBV
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; ------------------------------------------------------------------------
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.code
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doneirq:
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lda #7
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ldy IRQInd+1
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ldx IRQInd+2
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jmp SETVBV
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; ------------------------------------------------------------------------
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.segment "LOWCODE"
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IRQStub:
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cld ; Just to be sure
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.ifdef __ATARIXL__
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.ifdef CHARGEN_RELOC
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lda CHBAS
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pha
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.endif
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.endif
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lda PORTB
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pha
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.ifdef __ATARIXL__
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and #$FE ; disable ROM
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.endif
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ora #$10 ; map main memory into $4000..$7FFF area
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sta PORTB
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.ifdef __ATARIXL__
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set_chbase >__CHARGEN_START__
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.endif
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jsr callirq ; Call the functions
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pla
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sta PORTB ; restore old memory settings
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.ifdef __ATARIXL__
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.ifdef CHARGEN_RELOC
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pla
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sta CHBAS
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sta CHBASE
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.endif
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.endif
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jmp IRQInd ; Jump to the saved IRQ vector
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; ------------------------------------------------------------------------
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.segment "LOWBSS"
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IRQInd: .res 3
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.end
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