Subject: [stella] What Stella don't like... From: "Andrew Davie" <adavie@xxxxxxxxxxxxx> Date: Sun, 4 Mar 2001 22:47:27 +1100 |
Some reports of screen rolling on the Stella emulator had me stuck, for a while. It turns out that the following code was the problem... ldy #4 lda #D1 Synch sta WSYNC sta VSYNC ; start vertical synch dey bne Synch sty VSYNC This code was my 'optimised' beginning of vertical blank/screen stuff. Here's the non-optimised (ie: working) version.... lda #D1 ; requires D1 already in A sta WSYNC sta VSYNC ; start vertical synch sta WSYNC ; 1st sta WSYNC ; 2nd TV SYNCH (2 tested OK on PAL, 1 FAILED) sta WSYNC ; 3rd, to satisfy ES :) lda #0 sta VSYNC ; stop vertical synch Now, the first version (appears) to work OK under Z26, and also PCAE. I believe it works on the real thing, too - though I'm not exactly sure about that. But definitely causes screen-roll (and super-fast speed) under Stella. Looks like the handling of writes to VSYNC is causing the problem - stella doesn't like multiple writes. I have no idea if my optimised version is 'legal' or not, so I'm junking it, in order to maintain stella-support - but it's one for people to keep in mind :) Optimisation of Qb: -105 bytes :) Cheers A -- _ _ _| _ _ _| _ * _ _ , (_|| )(_|( (/_\/\/ (_|(_|\/(_(/_ ,~' L_|\ ,-' \ see my Museum of Soviet Calculators at ( \ http://www.taswegian.com/MOSCOW/soviet.html \ __ / L,~' "\__/ @--> v - Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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