| ??? 04/17/06 19:28 Read: times |
#114415 - USB logic analyzer Responding to: ???'s previous message |
Richard Erlacher said:
Full-speed, < 1.2 Mbps, USB is probably capable of 1 MHz transfers, but even if they're 1 KHz transfers, it has no impact on the sample rate. For the record, full-speed USB is 12 Mbps, not 1.2 Mbps. You could use a high-speed device (like Cypress EZ-USB FX2) and get 480 Mbps. Of course, these are the signalling limits and one expects transfer speeds on the half-duplex bus to be less. The sequence, ideally, would be, (1) set up trigger specification via USB, 1 hz PC-to-sampler transfer rate is adequate, well, almost; (2) perform sampling task, whatever that involves, resulting in data stored in buffer memory; (3) transfer resulting data to PC for processing and display, at whatever rate the USB channel and very slow, awkward, PC will provide. I suppose this depends on whether you're continually triggering the analyzer, or just doing one-shot (trigger, transfer, stop). If you're doing the latter, high-speed bulk transfers should be "fast enough." There are a handful of tricks one can do to speed things up. If you've got sufficient CPU horsepower in your USB analyzer "pod," you can do simple RLL coding of captured data (actually, do the RLL coding as the data are being captured and stored in the analyzer buffer). I'd suspect that simple data compressing like this will greatly improve transfer speed. There's no reason, BTW, that this has to be done under Windows, as DOS can do it. Assuming, of course, that one has a USB protocol driver stack for DOS. -a |
