40 lines
754 B
ArmAsm
40 lines
754 B
ArmAsm
; Function defined on pp272-273 of C64 Programmers Reference Guide
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ioinit:
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; Set $00/$01 port mode and value
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; We want BASIC and KERNAL ROMs mapped, and datasette motor off
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; (https://www.c64-wiki.com/wiki/Zeropage)
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LDA #$2F
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STA $00
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LDA #$27
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STA $01
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;; Compute's Mapping the 64, p156
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lda #$0e
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sta $D020
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lda #$06
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sta $D021
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;; Enable CIA1 IRQ and ~50Hz timer
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;; (https://csdb.dk/forums/?roomid=11&topicid=69037)
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lda #$7f
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sta $DC0D ; First disable all
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;; Set timer interval to ~1/50th of a second
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lda #<20000
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sta $dc04
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lda #>20000
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sta $dc05
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;; Enable timer interrupt
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lda #$81
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sta $dc0d
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;; Enable timer A to run continuously
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;; (http://codebase64.org/doku.php?id=base:timerinterrupts)
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lda #$11
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sta $dc0e
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lda $dc0d
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rts
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