Matt's collection of nick-nacks

Imaginary 6502 Emulator / Assembler (Work in progress)

; initialise device locations

device.display $200

; *** _Must_ initialise display ***
; display hardware regs at 0x200
org $200
; display at 0x300
; palette at palette
; 256 x 192 x 4bpp @ 25fps
dcw $300,palette,256,192,4,25

; *** Reset vector _must_ be set ***
org $FFFC
dcw start

; Program goes here
org $7000
start:
; stars will live at $0 and be a 16bit number for position
ldx #0

init:
jsr rand_8
sta 0,x 
inx

genagain:
jsr rand_8
cmp #$60
bcs genagain
clc
adc #$3 ; add screen base
sta 0,x
inx

cpx #192
bne init

draw:
ldx #192 ; index
jsr drawloop_clearStars

ldx #128 ; index
jsr drawloop_clearStars

ldx #64 ; index
jsr drawloop_clearStars

end:
jmp draw

drawloop_clearStars:

; clear star
lda #0
sta (0,x)

dec 0,x  ; subtract 1

txa
sta (0,x) ; draw star
dex
dex
bne drawloop_clearStars

frameloop:
lda $210 ; device.display +  16
bne frameloop
rts

; init rng

; rng with 2^32-1 length
rand_8:
asl r_seed
rol r_seed2
rol r_seed3
rol r_seed4
lda r_seed
bcc carry_not_set
eor #$AF
sta r_seed
carry_not_set:

rts

r_seed:
dcb 1
r_seed2:
dcb 14  ; prng seed byte, must not be zero
r_seed3:
dcb 2
r_seed4:
dcb 0

; *** Initialise palette ***
palette:
dcl 000000, $444444, $444444, $444444, $444444, $555555, $666666, $666666, $666666, $AAAAAA, $AAAAAA, $bbbbbb, $cccccc, $dddddd, $eeeeee, $ffffff

Feedback:

TODO