emailler/client/examples/raster.s

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.include "../inc/common.i"
print_a = $ffd2
SCREEN_RAM = $0400
COLOUR_RAM = $d800
VIC_CTRL_A = $d011
VIC_RASTER_REG = $d012
VIC_CTRL_B = $d016
VIC_MEMORY_CTRL=$d018
VIC_IRQ_FLAG = $d019
IRQ_VECTOR=$314
BORDER_COLOR = $d020
BACKGROUND_COLOR_0 = $d021
SCROLL_DELAY=4
CHARS_PER_LINE = 40
SCROLL_LINE=12
SCROLL_RAM = SCREEN_RAM+(SCROLL_LINE*CHARS_PER_LINE)
TOP_BORDER_SCAN_LINES = 50
BLACK = 0
WHITE = 1
RED = 2
CYAN = 3
PURPLE = 4
GREEN = 5
BLUE = 6
YELLOW = 7
ORANGE = 8
BROWN = 9
LIGHT_RED = 10
DARK_GRAY = 11
GRAY = 12
LIGHT_GREEN = 13
LIGHT_BLUE = 14
LIGHT_GRAY = 15
.macro wait_next_raster
lda VIC_RASTER_REG
:
cmp VIC_RASTER_REG
beq :-
.endmacro
.zeropage
temp_buff: .res 2
pptr: .res 2
.bss
.segment "STARTUP" ;this is what gets put at the start of the file on the C64
.word basicstub ; load address
basicstub:
.word @nextline
.word 2003
.byte $9e
.byte <(((init / 1000) .mod 10) + $30)
.byte <(((init / 100 ) .mod 10) + $30)
.byte <(((init / 10 ) .mod 10) + $30)
.byte <(((init ) .mod 10) + $30)
.byte 0
@nextline:
.word 0
.code
init:
lda #0
jsr clear_screen
lda #DARK_GRAY
sta BORDER_COLOR
lda #YELLOW
sta BACKGROUND_COLOR_0
sei ;disable maskable IRQs
lda #$7f
sta $dc0d ;disable timer interrupts which can be generated by the two CIA chips
sta $dd0d ;the kernal uses such an interrupt to flash the cursor and scan the keyboard, so we better
;stop it.
lda $dc0d ;by reading this two registers we negate any pending CIA irqs.
lda $dd0d ;if we don't do this, a pending CIA irq might occur after we finish setting up our irq.
;we don't want that to happen.
lda #$01 ;this is how to tell the VICII to generate a raster interrupt
sta $d01a
lda #$00 ;this is how to tell at which rasterline we want the irq to be triggered
sta VIC_RASTER_REG
ldax IRQ_VECTOR
stax old_irq
jsr set_next_irq_jump
cli ;enable maskable interrupts again
lda #23
@endless_loop:
nop
inc $ff
inc $400
tsx
stx $410
sta $411
ldy #$80
:
iny
bne :-
jmp @endless_loop
clear_screen:
ldx #$00
lda #$41
:
sta SCREEN_RAM,x
sta SCREEN_RAM+$100,x
sta SCREEN_RAM+$200,x
sta SCREEN_RAM+$300,x
sta COLOUR_RAM,x
sta COLOUR_RAM+$100,x
sta COLOUR_RAM+$200,x
sta COLOUR_RAM+$300,x
dex
bne :-
rts
set_next_irq_jump:
inc jump_counter
lda jump_counter
asl
asl
load_next_raster_entry:
tax
lda raster_jump_table,x ;bit 9 of raster to trigger on
cmp #$ff
bne not_last_entry
lda #0
sta jump_counter
jmp load_next_raster_entry
not_last_entry:
ora #$18 ;turn on bits 3 & 4
sta VIC_CTRL_A
lda raster_jump_table+1,x ;bits 0..7 of raster to trigger on
sta VIC_RASTER_REG
lda raster_jump_table+2,x ;LSB of IRQ handler
sta IRQ_VECTOR
lda raster_jump_table+3,x ;LSB of IRQ handler
sta IRQ_VECTOR+1
rts
exit_from_irq:
jsr set_next_irq_jump
jmp_to_original_irq_handler:
lda #$ff ;this is the orthodox and safe way of clearing the interrupt condition of the VICII.
sta VIC_IRQ_FLAG;if you don't do this the interrupt condition will be present all the time and you end
;up having the CPU running the interrupt code all the time, as when it exists the
;interrupt, the interrupt request from the VICII will be there again regardless of the
;rasterline counter.
old_irq = * + 1 ; Placeholder for self-modifying code
jmp $ffff
raster_irq:
ldax #synchronised_irq
stax IRQ_VECTOR
nop ; waste at least 12 cycles
nop ; (up to 64 cycles delay allowed here)
nop
nop
nop
nop
inc VIC_RASTER_REG ; At this stage, we have already moved to the next line
lda #1
sta VIC_IRQ_FLAG ; acknowledge the first raster interrupt
cli ; enable interrupts (the second interrupt can now occur)
ldy #9
dey
bne *-1 ; delay
nop ; The second interrupt will occur while executing these
nop ; two-cycle instructions.
nop
nop
nop
jmp jmp_to_original_irq_handler
synchronised_irq:
ldx VIC_RASTER_REG
nop
nop
nop
nop
nop
nop
nop
bit $24 ; 6569, 63 cycles/line
cpx VIC_RASTER_REG ; The comparison cycle is executed CYCLES or CYCLES+1 cycles
; after the interrupt has occurred.
beq :+ ; Delay by one cycle if $d012 hadn't changed.
; Now exactly CYCLES+3 cycles have passed since the interrupt
:
;now got a stable raster
nop
nop
nop
nop
nop
nop
nop
inc BORDER_COLOR
inc BACKGROUND_COLOR_0
ldx #20
@loop:
wait_next_raster
dex
bne @loop
dec BORDER_COLOR
dec BACKGROUND_COLOR_0
jmp exit_from_irq
.data
raster_jump_table:
;format:
;offset meaning
; $00 BIT 9 OF RASTER TO TRIGGER ON ($00 if bit 8 =0 , $80 if bit 8 =1)
; $01 BITS 0..7 OF RASTER TO TRIGGER ON
; $02 LSB OF ROUTINE TO JUMP TO
; $03 MSB OF ROUTINE TO JUMP TO
;table needs to end with a single byte $ff
;table needs to be sorted by scanlines
; .byte $0,$01
; .word scroll_text_irq
.byte $0,$81
.word raster_irq
; .byte $0,$80
; .word raster_irq
.byte $ff ;end of list
jump_counter: .byte 0