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153 lines
1.8 KiB
ArmAsm
153 lines
1.8 KiB
ArmAsm
;
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; Atari XL shadow RAM handlers
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;
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; Christian Groessler, chris@groessler.org, 2013
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;
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.if .defined(__ATARIXL__)
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.include "atari.inc"
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.include "save_area.inc"
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.import __CHARGEN_START__
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.export sram_init
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.export KEYBDV_wrapper
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.macro disable_rom
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lda PORTB
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and #$fe
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sta PORTB
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lda #>__CHARGEN_START__
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sta CHBAS
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sta CHBASE
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.endmacro
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.macro enable_rom
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lda PORTB
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ora #1
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sta PORTB
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lda #$E0
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sta CHBAS
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sta CHBASE
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.endmacro
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.segment "INIT"
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; Turn off ROMs, install system and interrupt wrappers, set new chargen pointer
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sram_init:
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; disable all interrupts
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sei
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ldx #0
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stx NMIEN ; disable NMI
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; disable ROMs
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disable_rom
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; setup interrupt vectors
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lda #<my_IRQ_han
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sta $fffe
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lda #>my_IRQ_han
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sta $ffff
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lda #<my_RESET_han
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sta $fffc
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lda #>my_RESET_han
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sta $fffd
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lda #<my_NMI_han
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sta $fffa
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lda #>my_NMI_han
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sta $fffb
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; setup pointers to CIOV and SIOV wrappers
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lda #$4C ; JMP opcode
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sta CIOV
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lda #<my_CIOV
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sta CIOV+1
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lda #>my_CIOV
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sta CIOV+2
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lda #$4C ; JMP opcode
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sta SIOV
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lda #<my_SIOV
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sta SIOV+1
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lda #>my_SIOV
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sta SIOV+2
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; enable interrupts
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lda #$40
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sta NMIEN
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cli
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rts
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.segment "LOWCODE"
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.macro int_wrap orgvec
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.local ret
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pha
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enable_rom
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lda #>ret
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pha
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lda #<ret
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pha
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php
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jmp (orgvec)
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ret: disable_rom
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pla
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rti
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.endmacro
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my_IRQ_han:
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int_wrap IRQ_save
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my_NMI_han:
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int_wrap NMI_save
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my_RESET_han:
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int_wrap RESET_save
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my_CIOV:
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pha
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enable_rom
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pla
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jsr CIOV_org
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php
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pha
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disable_rom
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pla
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plp
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rts
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my_SIOV:
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pha
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enable_rom
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pla
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jsr SIOV_org
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php
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pha
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disable_rom
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pla
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plp
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rts
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KEYBDV_wrapper:
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lda #>(kret-1)
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pha
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lda #<(kret-1)
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pha
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enable_rom
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lda KEYBDV+5
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pha
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lda KEYBDV+4
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pha
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rts ; call keyboard handler
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kret: pha
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disable_rom
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pla
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rts
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.endif ; .if .defined(__ATARIXL__)
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