mirror of
https://github.com/AndersBNielsen/6507SBC.git
synced 2024-09-21 10:37:24 +00:00
70 lines
2.2 KiB
ArmAsm
70 lines
2.2 KiB
ArmAsm
.feature string_escapes ; Allow c-style string escapes when using ca65
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.feature org_per_seg
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.feature c_comments
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RIOT = $80
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DRA = RIOT + $00 ;DRA ('A' side data register)
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DDRA = RIOT + $01 ;DDRA ('A' side data direction register)
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DRB = RIOT + $02 ;DRB ('B' side data register)
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DDRB = RIOT + $03 ;('B' side data direction register)
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READTDI = RIOT + $04 ;Read timer (disable interrupt)
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WEDGC = RIOT + $04 ;Write edge-detect control (negative edge-detect,disable interrupt)
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RRIFR = RIOT + $05 ;Read interrupt flag register (bit 7 = timer, bit 6 PA7 edge-detect) Clear PA7 flag
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A7PEDI = RIOT + $05 ;Write edge-detect control (positive edge-detect,disable interrupt)
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A7NEEI = RIOT + $06 ;Write edge-detect control (negative edge-detect, enable interrupt)
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A7PEEI = RIOT + $07 ;Write edge-detect control (positive edge-detect enable interrupt)
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READTEI = RIOT + $0C ;Read timer (enable interrupt)
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WTD1DI = RIOT + $14 ; Write timer (divide by 1, disable interrupt)
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WTD8DI = RIOT + $15 ;Write timer (divide by 8, disable interrupt)
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WTD64DI = RIOT + $16 ;Write timer (divide by 64, disable interrupt)
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WTD1KDI = RIOT + $17 ;Write timer (divide by 1024, disable interrupt)
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WTD1EI = RIOT + $1C ;Write timer (divide by 1, enable interrupt)
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WTD8EI = RIOT + $1D ;Write timer (divide by 8, enable interrupt)
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WTD64EI = RIOT + $1E ;Write timer (divide by 64, enable interrupt)
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WTD1KEI = RIOT + $1F ;Write timer (divide by 1024, enable interrupt)
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.segment "RODATA"
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.org $F000 ; Not strictly needed with CA65 but shows correct address in listing.txt
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nmi:
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irq:
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reset:
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cld ; Because you never know
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sei ; Probably not needed with the 6507
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;Set stack pointer and clear RAM
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ldx #$7f
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txs
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lda #0
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clearzp:
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sta $00,x
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dex
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bne clearzp
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sta $00,x
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lda #$FF
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sta DDRB ; Set whole B register to output
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; Reset state of DDRA is $00.
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main:
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inc DRB
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lda #244
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bit DRA
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bpl quartersecond
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sta WTD64DI ; 244*64 = 15616 ~= 16ms
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bne wait ; BRA
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quartersecond:
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sta WTD1KDI ; 244 * 1024 = 249856 ~= quarter second
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wait:
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lda READTDI
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bne wait ; Loop until timer runs out
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jmp main ; loop
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.segment "VECTORS6502"
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.ORG $fffa
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.word nmi,reset,irq
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.reloc
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