[sdiy] TOG news

[Tim Ressel]

Yo,

Well, after spending all morning wrestling with
software, I have a notion of the relative sizes of the
dividers that are needed to do a top-octave gennie. It
takes 10 macrocells to do a divider: nine for the
counter and one for the output compare. Its a problem
of the odd-ball counts. For example: for the C# output
I need a counter that resets at 451. But we want a
square wave on the output, so I need a magnatude
comparator set to go high with an input <= 225, that
being half of 451.

So 10 macrocells per output * 11 outputs = 110
macrocells. An XC95108 has 108 macrocells.

Just my luck.

So I can split the design into two smaller parts which
have 72 macrocells. And then I can take the advice of
Mr Blackett and put divider chains on each output.
Looks like I can put 2 divide-bys on each output. 

There is a problem with using all the macrocells,
however. The software has trouble routing all the
stuff when you use every last bit. It gets worse if
you try and have outputs come out of the chip in a
sensible order, rather that all willy-nilly as the
tool will do if left on its own.

This is not as easy as it looks!

--TR

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Its not the despair; I can handle the despair
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