[sdiy] Analysis of the TB-303 CPU timing

[Bruno Afonso]

Thanks for this work Julian, very interesting. A couple of notes:

1) For things like ISR and DAC, just write them out the first time they
appear ,i.e.: "interrupt service routine (ISR) " and then just use ISR
subsequently. This way for someone reading linearly from the beginning
everything is obvious.
2) some figures small and thus hard to see without zooming, maybe crop the
pics to the part that matter or that is critical to the point you're
making. Think about someone printing it, can they still see what you'd like
them to? If you can't crop to show the point you are trying to make, maybe
it's superfluous.
3) you mention jitter several times but there is no statistical description
of the phenomena (mean, std dev, etc) or even a graphic depiction such as
an histogram. Without this it's hard for the reader to see how relevant it
may or not be.

The article hinges on how interesting the 303 is due to the interplay of
clocks. You do not mention where you'd like to go next or what would be
useful to further explore. This is normally included in order to share
things that in your mind are important and left to uncover. A younger brave
soul may just try to pursue this, what a nice side effect! Personally, I
feel it would be cool to simulate the clock interplay to reproduce obseved
experimental data and then explore the space in order to get it more tight
or more loose. Would it have a big impact on sound and experience? Would
people care or notice if they used a much tighter 303 clock wise?

cheers
b

On Wed, Mar 15, 2017 at 11:14 AM Julian Schmidt <elfenjunge at gmx.net> wrote:

> I'm currently working on a TB-303 replacement CPU for the RE-303 project.
> www.http://sonic-potions.com/re303
>
> Since there is not too much information available, and a lot of
> speculations are running wild on the net, I tried to clear things up a bit.
>
> Someone from the RE-303 forums loaned me an original CPU and I hooked it
> up to a logic analyzer and did some extensive testing and measurement
> sessions.
>
> I summed up my findings in a short paper available here:
>
> http://sonic-potions.com/Documentation/Analysis_of_the_D650C-133_CPU_timing.pdf
>
> I have to admit, a lot of it is definitely from the "hear the fleas
> cough" category, as we say in Germany, but at least we now have data
> coming from a real CPU.
>
> Comments are welcome. I'm a bit rusty in writing proper papers ;)
>
> Best,
> Julian
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