Subject: Re: [stella] TIA Audio Polynomials From: Adam Wozniak <adam@xxxxxxxxxxxxxxxx> Date: Fri, 21 Nov 2003 12:54:57 -0800 (PST) |
On Fri, 21 Nov 2003, Thomas Jentzsch wrote: > Adam Wozniak wrote: > > Thanks for the pointer, but I'm still a little fuddled... > > I have searched the web a little bit more and found this website: > > http://ihome.ust.hk/~trippen/Cryptography/BM/frameset.html > > Very nice. Same results. Yes, I'd seen that. It seems you need to "double up" your input string to get correct results. You also need to initialize the LFSR with a piece of the pattern. Sort of makes sense, I guess. My current snag is that mode 15 works out to a 68 bit LFSR, and the "long long" in my current implementation is only 64 bits. *sigh* Here's what I know so far: C=0 set to 1 C=1 LFSR [4 3] C=2 LFSR [4 3] divide by 15 C=3 ???? C=4 divide by 2 C=5 divide by 2 C=6 divide by 31, with an average 52% duty cycle C=7 LFSR [5 3] (tia doc says 5 bit poly / 2; this is incorrect) C=8 LFSR [9 5] C=9 LFSR [5 3] C=10 divide by 31, with an duty cycle of 16/31 C=11 set last 4 bits to 1 C=12 divide by 6 C=13 divide by 6 C=14 divide by 93, with a duty cycle of 16/31 C=15 [68 68 67 66 65 63 62 37 36 35 34 32 31 6 5 4 3 1] (maybe) Note the duty cycle is 16/31 for the divide by 31 modes, NOT 18/31 as in the Stella emulator. Still working on testing the polynomial for mode 15. Still haven't cracked into mode 3 yet. -- adam@xxxxxxxxxxxxxxxx http://cuddlepuddle.org/~adam/pgp.html Will code for food. http://cuddlepuddle.org/~adam/resume.html "The dinosaurs are not around today because they did not have a space program." -- Arthur C. Clarke ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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