30 lines
571 B
ArmAsm
30 lines
571 B
ArmAsm
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;;
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;; Official Kernal routine, described in:
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;;
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;; - [RG64] C64 Programmer's Reference Guide - page 301
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;; - [CM64] Compute's Mapping the Commodore 64 - page 232
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;;
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;; CPU registers that has to be preserved (see [RG64]): .Y
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;;
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stop:
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;; Bit 7 of STKEY contains the state of the STOP key
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;; (Compute's Mapping the 64, p27)
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;; BASIC checks carry flag to indicate STOP or not
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lda STKEY
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and #$80
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beq stop_pressed
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;; By trial and error, we know that Z + C = BREAK
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;; and that neither should be set otherwise
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lda #$ff
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clc
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rts
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stop_pressed:
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sec
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lda #$00
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rts
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