On Mon, Nov 03, 2014 at 06:12:11PM +0100, Jan Kiszka wrote: > On 2014-11-03 09:03, Jeroen Van den Keybus wrote: > >> I try to write a hard real time usb driver. I communicate my device using > >> open(), read() etc. My device is a gpio module. > > > > > > I assume you want to control an USB host controller using a GPIO interface ? > > > > > >> I am coding a kernel module > >> to communicate the device using xenomai on real time. But I am not sure > >> that this way is reasonable. If I should going on this way, what should I > >> implement? Could you give me some example or link to write hard real time > >> usb driver for* physical* device? > > > > > > I cannot help you with that, but one important issue to consider is that > > the USB protocol itself operates with small, hardware controlled time slots > > of 1 ms (USB1.x) or 125 usec (USB2.0). You may therefore need a significant > > amount of software to properly distribute real-time traffic in these - > > essentially asynchronous - slots. The latency of a real-time process > > waiting for USB data can therefore also be as large as the time slot > > duration. If your real-time requirements are modest, you may be able to > > live with that. Still, count on a major software effort: just have a look > > at the Linux USB driver framework. > > > > Alternatively, you could check if you can synchronize your real-time > > process with the USB controller frame rate. > > > > FWIW, we still don't have USB 2.0 support (though I vaguely remember > previous efforts in that direction),
There is one here: http://sourceforge.net/projects/usb20rt.berlios/ Have not looked at the code though. -- Gilles. _______________________________________________ Xenomai mailing list [email protected] http://www.xenomai.org/mailman/listinfo/xenomai
