mirror of https://github.com/cc65/cc65.git
83 lines
1.8 KiB
ArmAsm
83 lines
1.8 KiB
ArmAsm
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; Atari XL shadow RAM timer IRQ #2 handler
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;
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; Christian Groessler, chris@groessler.org, 2019
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;
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;DEBUG = 1
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.ifdef __ATARIXL__
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SHRAM_HANDLERS = 1
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.include "atari.inc"
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.include "romswitch.inc"
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.import __CHARGEN_START__
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.export set_VTIMR2_handler
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.segment "LOWBSS"
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VTIMR2_handler: .res 3
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.segment "BSS"
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old_VTIMR2_handler:
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.res 2
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.segment "LOWCODE"
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; timer interrupt handler:
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; disable ROM, call user handler, enable ROM again
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my_VTIMR2_handler:
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disable_rom_quick
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jsr VTIMR2_handler
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enable_rom_quick
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pla
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rti
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.segment "CODE"
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; install or remove VTIMR2 handler
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; input: CF - 0/1 for remove/install handler
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; AX - pointer to handler (if CF=1)
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; registers destroyed
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set_VTIMR2_handler:
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bcc @remove
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; install vector
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stx VTIMR2_handler+2
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sta VTIMR2_handler+1 ; save passed vector in low memory
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lda #$4C ; "JMP" opcode
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sta VTIMR2_handler
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lda VTIMR2
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sta old_VTIMR2_handler
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lda VTIMR2+1
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sta old_VTIMR2_handler+1
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lda #<my_VTIMR2_handler
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php
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sei
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sta VTIMR2
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lda #>my_VTIMR2_handler
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sta VTIMR2+1
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plp
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rts
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@remove: php
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sei
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lda old_VTIMR2_handler
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sta VTIMR2
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lda old_VTIMR2_handler+1
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sta VTIMR2+1
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plp
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rts
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.endif ; .ifdef __ATARIXL__
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