Subject: Re: [stella] 12 chars/line!? From: Jim Nitchals <jimn8@xxxxxxxxxx> Date: Fri, 26 Sep 1997 13:42:19 -0700 (PDT) |
> > Yes, this will need just one mask operation (2 cycles) vs. 4 ASLs (8 > cycles), or a savings of 6 cycles per byte written, or 180 cycles for a > 30 byte transfer. But still, at a minimum, you will be: > > reading the first character (min. 4 cycles) > reading the second character (min. 4 cycles) > masking the second character (2 cycles) > combining the characters (3 cycles) > writing the combined character (min. 4 cycles) > adjusting indexes (min. 4 cycles) > looping (3 cycles) If you use two font tables, you can skip the mask. I've got the code to render text this way. It works. But... The BIGGER problem is: how do you *really* display it? Using two players, three copies mode, there are only 2 2/3 CPU cycles between needs to write to GRP0 and GRP1 (alternately.) It's going to be a squeaker. Best as I can tell, the leftmost bit of the last byte of graphics will not come through correctly: Preload GRP0 and GRP1 with the left two bytes of graphic data, and load A, X, Y with the next 3. 1/3 cycle before GRP0 starts displaying (have to find a horizontal pos. that works for that), write A to GRP0. The write finishes at cycle 2 2/3, exactly as GRP1 starts displaying. Write X to GRP1. The write finishes at cycle 5 2/3, 1/3 cycle past the start of the next GRP0 display. Write Y to GRP0. The write finishes at cycle 8 2/3, 2/3 cycle past the start of the next GRP1 display. You're out of CPU time. A LDA #0, STA GRP1 takes 5 cycles, putting you at cycle 13 2/3. You're 1/3 of a cycle late, and the last image is trashed. The only question is how badly... could be just the leftmost pixel. -- 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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