## Re: [stella] TIA Audio Polynomials

 Subject: Re: [stella] TIA Audio Polynomials From: Adam Wozniak Date: Fri, 21 Nov 2003 12:54:57 -0800 (PST)
```On Fri, 21 Nov 2003, Thomas Jentzsch 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.

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