Re: 6561 Die Shot Reversing Explorations
Posted: Wed Sep 18, 2019 6:28 am
No, I don't think that will match because yesterday I simulated all possible combinations, changing speeds, connections and so on, but nothing of what I tried matched the real VIC-20 output.
I now believe the LFSR is running at the correct speed because of the loop cycle length, and also the audio is running at the correct speed (twice faster than CR-C as you initially proposed), that is confirmed by the fact that the smallest wavelength increment does matches the VIC-20 one.
But for some reason our model is outputting shorter runs of "0"s and "1"s... I just don't know why.
Today I extracted the "bits" from the real audio waveform, decoding it as if it was a sort of digital transmission. It wasn't easy because it required precise clocking, but luckily I was able to derive a clock correction from the signal itself.
Illustrated in the picture below:
Inspecting the bitstream I verified it repeats every 65535 bits, which is indeed the length of the LFSR cycle.
Now that we have the actual bits coming from the 8bit SR, I'll use them in my debugs, hoping that will lead to some new insight. I attached the file in case you want to run your own experiments on it. Tell me if you want it in some other form (JSON or else).
I now believe the LFSR is running at the correct speed because of the loop cycle length, and also the audio is running at the correct speed (twice faster than CR-C as you initially proposed), that is confirmed by the fact that the smallest wavelength increment does matches the VIC-20 one.
But for some reason our model is outputting shorter runs of "0"s and "1"s... I just don't know why.
Today I extracted the "bits" from the real audio waveform, decoding it as if it was a sort of digital transmission. It wasn't easy because it required precise clocking, but luckily I was able to derive a clock correction from the signal itself.
Illustrated in the picture below:
Inspecting the bitstream I verified it repeats every 65535 bits, which is indeed the length of the LFSR cycle.
Now that we have the actual bits coming from the 8bit SR, I'll use them in my debugs, hoping that will lead to some new insight. I attached the file in case you want to run your own experiments on it. Tell me if you want it in some other form (JSON or else).