I'm trying to write a simple logic analyzer to run on the PIC 32. It will
poll a pin (or pins) (either via interrupt on change, or preset sampling
rate), and send data to the PC via USB. A few questions:


1. How should I manage the USB transfers? There's not enough RAM on the PIC
to store and then transfer all at once, so I'm not even going to bother. I'=
m
going to transfer on the fly, as it's sampling. I don't need more than 1
MSPS anyway, so this should be fine.

Should I transfer a byte at a time? 64 bytes at a time? 30kB at a time?
How I have it set up now is the PIC32 running at maximum performance at
80MHz and Timer1 prescaled 1:8, and loaded with a period of 10. So the tick
frequency is 1MHz. Every time the a timer goes off, an interrupt occurs, an=
d
the pin is sampled. The ISR itself handles the loading of the buffers, etc.
(Is that the right way to do it)? So should it call a USB transfer every
byte? 64 bytes? 30kB?

Note: I'm using the generic USB package from the Microchip application
libraries by the way, so simple generic USB bulk transfers.

Is there a faster way to stream data through USB while sampling?

2. I looked into DMA transfers to USB, but it was impossible to search for
any examples, and it looks pretty complicated, so I don't know.

3. The other option is to get 128MB of DRAM from somewhere and hook up to
the PIC, but DRAM interfacing will be pretty complicated, and I want to kee=
p
it simple.

Other than that, I'm out of ideas for now.

What's the main concept for sampling fast and transferring on the fly? Or i=
s
that not possible?
--=20
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