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29d1400340
_sys() is supposed to be (primarily) intended to call ROM routines. Leveraging the "file overlay" mechanism of the cc65 build system allows to provide a Apple II specific _sys() implementation that temporarily switches in the ROM.
82 lines
1.7 KiB
ArmAsm
82 lines
1.7 KiB
ArmAsm
;
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; void __fastcall__ _sys (struct regs* r);
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;
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.export __sys
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.import jmpvec
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.include "zeropage.inc"
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.segment "LOWCODE"
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__sys: sta ptr1
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stx ptr1+1 ; Save the pointer to r
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; Fetch the PC and store it into the jump vector
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ldy #5
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lda (ptr1),y
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sta jmpvec+2
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dey
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lda (ptr1),y
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sta jmpvec+1
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; Remember the flags so we can restore them to a known state after calling the
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; routine
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php
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; Get the flags, keep the state of bit 4 and 5 using the other flags from
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; the flags value passed by the caller. Push the new flags and push A.
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dey
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php
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pla ; Current flags -> A
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eor (ptr1),y
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and #%00110000
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eor (ptr1),y
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pha ; Push new flags value
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ldy #0
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lda (ptr1),y
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pha
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; Get and assign X and Y
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iny
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lda (ptr1),y
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tax
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iny
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lda (ptr1),y
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tay
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; Switch in ROM
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bit $C082
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; Set A and the flags, call the machine code routine
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pla
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plp
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jsr jmpvec
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; Back from the routine. Save the flags and A.
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php
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pha
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; Switch in LC bank 2 for R/O
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bit $C080
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; Put the register values into the regs structure
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tya
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ldy #2
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sta (ptr1),y
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dey
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txa
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sta (ptr1),y
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dey
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pla
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sta (ptr1),y
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ldy #3
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pla
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sta (ptr1),y
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; Restore the old flags value
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plp
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; Done
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rts
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