On Sun, Feb 23, 2014 at 06:27:17AM +0000, Luke-Jr wrote: > If I understand the USB Serial code correctly, at least open devices are > constantly polled by 2 active URBs replaced immediately upon completion, > except when the tty layer throttles them. As Greg mentioned, it depends on what driver you're using but the generic implementation, which most drivers use, has two bulk-in urbs. > With many of these devices, this creates significant USB bandwidth usage. At > least one report found that it starts creating practical problems after 12 > devices (on a BeagleBone), while adding a delay allows up to 60. What driver are you using here? In general this should not cause any problems, but for example the ftdi_sio driver has the low-latency flag set by default which results in bulk-in data (mostly empty, status-only packets) being received every millisecond. If the flag is cleared (e.g. using setserial) the latency can be increased through sysfs (defaults to 16ms). Johan -- 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
