[ColorForth] USB in ColorForth

[Jeff Fox <fox@xxxxxxxxxxxxxxxxxxx>]

John Drake wrote:
 
> gathered from the spec the F21 network coprocessor
> would be able to handle USB without breaking a
> sweat.

The serial coprocessor on the F21d prototype is
not actually mine.  It is not the network router
that was on my previous chips.  Due to the
considerable constraints at the time I did
get a chip out with a simpler serial coprocessor.
I have not published the specs on the serial
coprocessor on the prototype that I have.
Perhaps it would make the part look more
attractive to some people.  Not so strange.

It actually has serial in and serial out processors
with DMA.  Registers set the clock rate and bit
pattern.  There is still only so much bandwidth
with the types of memories it uses.  I have
not pushed it to the limit but it looked 
quite stable at 33Mhz.

So the device is simpler and the software to drive
it is a little different than the software that
would be needed for the unit on F21c with packet
routing built in.  But that unit would make
distributed shared memory trivial.  It will take
a tiny bit more code with the simple serial
unit.

The I/O pins that connect to the serial I/O
coprocessor and that provide hardware flow
control can also be used as general purpose
digital I/O pins on the PPort.  So the same
functionality can be provided entirely in
software on the same pins at lower data
rates.

I almost got F21 tweaked as relacement for
8051 based USB products.  They could have made
it on their same fab and increased the througput
of their part by a huge factor.  That is the
kind of thing where a little money would have
been handy.  $50 more dollars and I probably
could have sold 480M chips on that deal. ;-)
 
Jeff Fox

"731 HOP" ;-)
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