Subject: [stella] code incompatible with stella emulator From: Jim Crawford <pfister@xxxxxxxxxxxxxx> Date: Wed, 15 Oct 1997 07:54:54 -0700 (PDT) |
i just learned to code for the 2600 a few hours ago and wrote this (or rather, modified it slightly from howtodrw.s (which, incidentally, doesn't work under stella 0.7 at all -- it says there's a bad opcode but rudely refuses to tell me which opcode or memory location)) this seems odd to me... the following code works fine under PCAE, but not under Stella. i can't test it on a real atari myself, so i can't tell which is right :) can someone tell me what's going on? (assembled under DASM v2.02) processor 6502 org $f000 vsync equ $00 ;wait for vertical retrace vblank equ $01 ;vertical blank wsync equ $02 ;wait for horizontal retrace colubk equ $09 ;background color intim equ $284 ;timer read tim64t equ $296 ;timer write beginy equ $80 start sei ;disable interrupts cld ;clear bcd math bit ldx #$ff ;set stack pointer txs lda #0 ;clear memory clearloop sta 0,x dex bne clearloop mainloop jsr vertblank inc beginy jsr drawscreen jmp mainloop vertblank sta vsync ;wait for vsync sta wsync ;wait for 3 scanlines sta wsync sta wsync lda #44 ;set timer for 37 blank scanlines. sta tim64t ;why 44? i didn't calculate it :) rts drawscreen lda intim ;wait for vblank period to end bne drawscreen sta wsync ;first scanline sta vblank ;turn blanking off ldx #191 ;191 scanlines left... ldy beginy ;start of color cycle scanloop sty colubk ;update background color sta wsync ;wait for vsync dey ;next color dex bne scanloop lda #$ff sta wsync ;last one sta vblank ;turn blanking on for overscan rts org $f7fc .word start ;entry point .word start ;int vector -- pf / green grapes / xantis "The PowerPC is something that should be shown to small children when they have been very bad." --Linus Torvalds -- Archives updated once/day at http://www.biglist.com/lists/stella/archives/ Unsubscribing and other info at http://www.biglist.com/lists/stella/stella.html
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