On Thu, 2011-09-29 at 14:06 -0400, V G wrote:
> When capturing multiple channels and data through the bus.

Fine, but how many logic probes will you have? 8? 16? Even with 16
you've got 15k samples, still MORE then enough for pretty much all debug
work you'll have.

> Yes, that's what I thought of initially, but there are problems:
>=20
> 1. If I burst large chunks of data to the PC, the PIC will either miss a =
few
> samples during the transfer process, OR
>=20
> 2. If the sampling is done in a high priority interrupt, then the USB
> protocol will get interrupted.

Interesting, I'm not familiar with the PIC's USB peripheral, does it
require that much hand holding? You can't just set up a bunch of stuff
and tell it to "go"?=20

If true you're right, and I'd say a PIC isn't the correct tool to use in
this case.

Have you considered using an FPGA? I've done this sort of thing before,
if you are familiar with FPGAs this sort of project becomes rather
trivial.

> > 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).
> >
>=20
> Yeah, that's true. But then I'd have to use CPU clock cycles to compress =
on
> the fly. I don't know if I can still get my 10 Msps target with any of th=
ese
> options give that the max speed is 80MHz.

Very true, again, considering your requirements, and how "messy" USB can
be (I'm worried you're "on the fly" solution will never work due to
latency on the PC side servicing the USB port), I think you should
consider a change of target.

FWIW I built a very basic serial port based logic analyzer many years
ago:

http://repatch.dyndns.org/pic_stuff/logan/index.html

(it's actually quite embarrassing looking at that project now, the code
is a such a mess, and the design is really crude).

In that I decided on a RAM chip for data storage, a CPLD to address and
clock it, and a 16F877 PIC to do all the other good stuff. It was a
really fun project and I actually used it's for real work a few times.

TTYL

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.