On Sat, Dec 18, 2010 at 02:41:11AM +0000, pevnev@xxxxxxxx wrote: > Hi, > > I have Fedora 12 running on dual CPU (0.8 - 1.6 GHz) Intel based Lap Top with single USB port > This USB port is directly (no USB hub) connected to FTDI's FT2232HL > USB device (which is integrated into Xilinx FPGA of the custom board) > which is continuously sending data to usb port at > Lap Top at speed from 8 to 11 GByte/sec The application software > (based on FTDI's D2XX API interface) ,which is trying to receive this > data, is running on that LapTop ToughBook as a real time task. > The FTDI's D2XX API interface supplies the call to check whether data > is locally available and another call to read it out. > Typically the data bytes are available at intervals between 3 and 20 > msec but sometimes the data is absent for 120 msec and longer .. > The USB wireshark analyzer, installed on that Lap Top, shows that > data is flowing continuously > What debugging does Linux USB interface has (as built-in) to invoke in > order to see what causes such long (120 msec and longer) delays > ? USB does not work well, if at all, in "real time" situations as the bus is completely undeterministic. I would look to your device for the delay in timing, or make sure that your userspace program has sent a request for the data properly, to try to track down the issue. But again, relying on USB in real time systems is prone to failure. Lots of people have tried and ignored our warnings about this over the years, only to have huge issues and eventually agreed with us. So please be aware of the inherent issues in USB that keep it from being a proper solution to your problem. good luck, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
