using USB devices. The main issue I haven't got straighten out yet is the difference between BULK / INTERRUPT urb's. Can anyone please give me a hint on what kind of message flow to expect when using interrupt endpoints. I have read some of the source in the driver/usb directory but as I said - I'm not that familiar with USB.
What would you propose to start with?
Grab the USB 2.0 spec and give the relevant sections a skim; you should
really have it for reference when doing USB programming. That's for the
protocol and device model. For 2.6, use the kerneldoc ("make pdfdocs"),
much of which is also relevant for 2.4 (and 2.2) kernel APIs.Interrupt transfers use reserved bandwidth, and periodically issue transfers. The periods are 2^N units, units are "frames" at full or low speeds and "microframes" (8/frame) at high speed. The transfers can be 0-8 bytes at low speed, 0-64 at full speed, 0-3072 at high speed.
In Linux 2.6 there's no other difference in message flow between bulk and interrupt transfers.
In Linux 2.4 there's an armload of special cases. For example, there's an "automagic resubmit" mechanism, and you can't necessarily queue interrupt transfers.
- Dave
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