dos33fsprogs/music/ksp_theme/interrupt_test.s

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