-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 > So, my boss asks me today, "why can't we send a usb message out every > single millisecond?" in response to my statement that there is an > approximately 4 millisecond delay between a message being sent and > getting a reply from the device. The current driver we're using utilizes > the newest version of urb chaining in isochronous mode. If I were to go > about trying to explain to him why this delay is present in the system, > what would I say? I assume that it takes 2 ms to load and send to the > device and another 2 ms for the device to load and send data back to me. > Am I correct? Why is there a 2 ms delay? Is the 1st millisecond a > "preparation" phase?
IIRC, latency is much lower than that. (I think I've hit sub-1ms pings over usbnet to a StrongARM.) 1ms is a rather long time on recent hardware. However, if the USB bus is congested (there are lots of other devices that are bandwidth intensive, for example if some moron has 126 quickcams plugged in and one of your devices), you will likely not be able to send data that quickly - so don't count on it. For more information, read the USB spec. It's got everything you will want to know about USB in it. :) > Anton /j - -- Joshua Wise | www.joshuawise.com GPG Key | 0xEA80E0B3 Quote | <lilo> I akilled [EMAIL PROTECTED] by mistake -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.2 (GNU/Linux) iD8DBQE/lHr+Pn9tWOqA4LMRAnJcAJwKKkapsW14MRfjxmcxqV+fejiODgCcCSFp pf2P21EZFSKjjnMOBx2rsEc= =skeJ -----END PGP SIGNATURE----- ------------------------------------------------------- This SF.net email is sponsored by OSDN developer relations Here's your chance to show off your extensive product knowledge We want to know what you know. Tell us and you have a chance to win $100 http://www.zoomerang.com/survey.zgi?HRPT1X3RYQNC5V4MLNSV3E54 _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
