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60 lines
1.4 KiB
ArmAsm
60 lines
1.4 KiB
ArmAsm
;
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; IRQ handling (C128 version)
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;
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.export initirq, doneirq
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.import callirq
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.include "c128.inc"
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IRQInd = $2FD ; JMP $0000 - used as indirect IRQ vector
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; ------------------------------------------------------------------------
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.segment "INIT"
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initirq:
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lda IRQVec
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ldx IRQVec+1
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sta IRQInd+1
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stx IRQInd+2
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lda #<IRQStub
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ldx #>IRQStub
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jmp setvec
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; ------------------------------------------------------------------------
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.code
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doneirq:
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lda IRQInd+1
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ldx IRQInd+2
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setvec: sei
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sta IRQVec
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stx IRQVec+1
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cli
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rts
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; ------------------------------------------------------------------------
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; The C128 has ROM parallel to the RAM starting from $4000. The startup code
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; above will change this setting so that we have RAM from $0000-$BFFF. This
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; works quite well with the exception of interrupts: The interrupt handler
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; is in ROM, and the ROM switches back to the ROM configuration, which means
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; that parts of our program may not be accessible. To solve this, we place
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; the following code into a special segment called "LOWCODE" which will be
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; placed just above the startup code, so it goes into a RAM area that is
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; not banked.
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.segment "LOWCODE"
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IRQStub:
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cld ; Just to be sure
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lda MMU_CR ; Get old register value
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pha ; And save on stack
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lda #MMU_CFG_CC65 ; Bank 0 with kernal ROM
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sta MMU_CR
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jsr callirq ; Call the functions
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pla ; Get old register value
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sta MMU_CR
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jmp IRQInd ; Jump to the saved IRQ vector
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