On Thu, Sep 29, 2011 at 1:41 PM, Herbert Graf wrote: > 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 > can > > store 250k samples on the PIC32 RAM itself if I wanted to. I either nee= d > 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? > When capturing multiple channels and data through the bus. > 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. > Yes, that's what I thought of initially, but there are problems: 1. If I burst large chunks of data to the PC, the PIC will either miss a fe= w samples during the transfer process, OR 2. If the sampling is done in a high priority interrupt, then the USB protocol will get interrupted. > 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). > 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 thes= e options give that the max speed is 80MHz. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .