39 lines
983 B
ArmAsm
39 lines
983 B
ArmAsm
.define Blm, Blmnp
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.sect .text
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.sect .rom
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.sect .data
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.sect .bss
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.sect .text
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! This subroutine copies bytes from one place in memory to
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! another. The source address is in registerpair AX and is stored
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! in zeropage locations ADDR and ADDR+1.
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! The destination address is popped from the stack and stored in
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! zeropage locations ADDR+2 and ADDR+3.
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! The number of bytes to be copied is in register Y (lowbyte) and
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! zeropage location NBYTES+1 (highbyte).
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! The subroutine Blmnp is used when the source and destination
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! addresses are already in zeropage.
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Blm:
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stx ADDR+2 ! source address (lowbyte)
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sta ADDR+3 ! source address (highbyte)
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jsr Pop
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stx ADDR ! destination address (lowbyte)
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sta ADDR+1 ! destination address (highbyte)
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Blmnp: ldx NBYTES+1
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1: dey
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lda (ADDR),y ! get source byte
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sta (ADDR+2),y ! copy to destination
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tya
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bne 1b
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dec ADDR+1 ! 256 bytes copied
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dec ADDR+3 ! decrement source and destination address
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ldy #0
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dex
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bne 1b ! do it n times
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rts
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