2018-02-06 06:30:20 +00:00
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; Test the 6522 on a Mockingboard running in interrupt mode
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; Trying to set it to 50Hz
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.include "zp.inc"
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;=============================
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; Print message
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;=============================
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jsr HOME
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jsr TEXT
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lda #0
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sta DRAW_PAGE
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sta CH
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sta CV
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lda #<mocking_message
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sta OUTL
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lda #>mocking_message
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sta OUTH
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jsr move_and_print
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jsr mockingboard_detect_slot4
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cpx #$1
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beq mockingboard_found
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lda #<not_message
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sta OUTL
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lda #>not_message
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sta OUTH
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inc CV
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jsr move_and_print
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jmp forever_loop
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mockingboard_found:
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lda #<found_message
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sta OUTL
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lda #>found_message
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sta OUTH
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inc CV
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jsr move_and_print
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;=========================
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; Setup Interrupt Handler
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;=========================
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; Vector address goes to 0x3fe/0x3ff
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; FIXME: should chain any existing handler
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lda #<interrupt_handler
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sta $03fe
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lda #>interrupt_handler
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sta $03ff
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;============================
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; Enable 50Hz clock on 6522
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;============================
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lda #$40 ; Generate continuous interrupts, don't touch PB7
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sta $C40B ; ACR register
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lda #$7F ; clear all interrupt flags
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sta $C40E ; IER register (interrupt enable)
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lda #$C0
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sta $C40D ; IFR: 1100, enable interrupt on timer one oflow
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sta $C40E ; IER: 1100, enable timer one interrupt
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lda #$E7
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sta $C404 ; write into low-order latch
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lda #$4f
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sta $C405 ; write into high-order latch,
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; load both values into counter
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; clear interrupt and start counting
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; 4fe7 / 1e6 = .020s, 50Hz
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;============================
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; Enable 6502 interrupts
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;============================
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;
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cli ; clear interrupt mask
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;============================
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; Loop forever
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;============================
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lda #64
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forever_loop:
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; clc
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; adc #1
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sta $0401
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jmp forever_loop
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;=============================
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; simple interrupt handler
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;=============================
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2018-02-07 17:44:37 +00:00
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; On Apple II/6502 the interrupt handler jumps to address in 0xfffe
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; This is in the ROM, which saves the registers
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; on older IIe it saved A to $45 (which could mess with DISK II)
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; newer IIe doesn't do that.
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; It then calculates if it is a BRK or not (which trashes A)
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; Then it sets up the stack like an interrupt and calls 0x3fe
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2018-02-06 06:30:20 +00:00
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2018-02-07 17:44:37 +00:00
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interrupt_handler:
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pha ; save A
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2018-02-06 06:30:20 +00:00
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bit $C404 ; can clear interrupt by reading T1C-L
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inc $0410 ; increment text char on screen
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pla ; restore A
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rti
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;=========
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;routines
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;=========
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.include "../asm_routines/gr_offsets.s"
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.include "../asm_routines/text_print.s"
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.include "../asm_routines/mockingboard.s"
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;=========
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; strings
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;=========
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mocking_message: .asciiz "LOOKING FOR MOCKINGBOARD IN SLOT #4"
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not_message: .byte "NOT "
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found_message: .asciiz "FOUND"
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done_message: .asciiz "DONE PLAYING"
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