Subject: Re: [stella] problems with monitor syncing From: Chris Wilkson <ecwilkso@xxxxxxx> Date: Tue, 3 May 2005 15:03:31 -0400 |
It's hard to tell much from the pictures. But here's my guess... The VGA horizontal frequency is ~ twice that of the TIA: 31kHz vs. 15.7kHz The vertical frequency is also somewhere "near" twice as fast, though there is a lot more variation due to the software control of the TIA's vertical timing. If you're not already doing it, you're going to need a line buffer. The TIA should write video to the buffer, and the buffer should be played twice to the VGA output. I think the easiest way to do this is the following: during TIA scanline n, the TIA fills buffer A. During TIA scanline n+1, the TIA fills buffer B while buffer A is being read by the VGA output (twice), etc. There's a lot of hardware overhead, and the SYNC signals are tricky, because the 2 horizontal frequencies are not integer multiples. But it works. I'm sure there are more elegant solutions for building a non-integer line buffer, but you get the idea. I ran into similar problems (in reverse) a long time ago when I tried to double the 2600 clock speed and output it to a TV. The first thing I tried was masking every other hsync pulse. I wound up with a display similar to yours. IIRC, I had 4 psuedo-copies of Combat on screen at once. But I did finally make it work, so keep hacking at it! :) -Chris On Mon, 2 May 2005, Adam Wozniak wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > http://cuddlepuddle.org/~adam/help/ > > These are images of my FPGA TIA driving my VGA monitor. (Space Invaders, > if you can't tell.) > > It looks as though the monitor cannot sync to the horizontal frequency > I'm giving it. The image is totally stable vertically (i.e. no rolling > or anything), but it looks as though each line is wrapped around the > screen twice (one and a half times?). Look closely at the score; note > the large gaps between pixels, both horizontally and vertically. > > Unfortunately I don't have a scope handy to measure frequencies. > > Is it possible my hsync is correct, but that my monitor sucks? Or have > I done something else wrong? > > - -- > adam@xxxxxxxxxxxxxxxx http://cuddlepuddle.org/~adam > KG6GZR http://cuddlepuddle.org/~adam/resume.html > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.2.1 (GNU/Linux) > > iD8DBQFCdp1pyvXf5Z0z5zERAuvxAKCNFPU0E2ltmRXzS+0KOfC9/53gAQCgq/pS > Ovu7GW2UmF9bIkEK/w8i01Y= > =iU9J > -----END PGP SIGNATURE----- > > Archives (includes files) at http://www.biglist.com/lists/stella/archives/ > Unsub & more at http://stella.biglist.com > > Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://stella.biglist.com
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