On Thu, 2011-09-29 at 13:17 -0400, V G wrote:
> The only problem I have with these is that 256K samples isn't enough. I c=
an
> store 250k samples on the PIC32 RAM itself if I wanted to. I either need =
to
> stream it to the host on the fly, or need some cheap DRAMs.

I'm confused, if you can store 250k samples in the PIC, why do you want
to bother with "on the fly" type stuff? When is 250k samples not enough?

Alot of the work I do requires at most a few hundred samples. Thousands
is rare. 250k? I'd say you should refine your triggering so that you
don't need such a large window. Alot of people I've worked with started
out thinking they needed millions of samples to get their work done.
They quickly learned that small sample windows triggered at the right
point are FAR more useful to quickly debugging an issue.

If 250k is REALLY not enough, you STILL don't need "on the fly". Create
a large ring buffer in the PIC to store your samples, and on an
interrupt check that buffer and if it's fills beyond a certain amount,
shoot a large chunk of it to the PC over USB. That way you don't have to
worry about traffic on the USB bus, or the PC not responding quickly
enough to you.

Another option, which is either very easy or very hard is to compress
your data. Logic analyzer waveforms are usually VERY compressible
(almost all the data is relatively static, or is a clock in which case
you just have to define the period).

TTYL


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