hi alan: thanks for your kind help :) 2010/11/22 Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>: > On Sun, 21 Nov 2010, vichy wrote: > >> Dear all: >> I know an usb packet transaction is 125 micro second and I see the > > No. A USB microframe is 125 us. Packet transmissions are much > shorter. > >> USB_CTRL_GET_TIMEOUT is 5000 ms. >> If I try to send vendor specific command to control pipe for get >> status of my dongle, which is 4 byes data long, can I shorten the >> timeout value as 75 ms? > > Certainly. You can set the timeout value to whatever you want. But if > you set it too short, the transfer will time out instead of completing > normally. > >> I try to set this value but I get timeout error in usb_start_wait_urb. >> But 75ms seems longer enough for 125 micro second per transaction. > > Transaction != transmission. However, it is true that every high-speed > transaction must end within 125 us. Every full-speed or low-speed > transaction must end within 1000 us. > > A control transfer contains at least 2 transaction stages (Setup and > Status), and the time interval between them can be much longer than > 1000 us. > >> why I still get the time out error? >> ( I have monitored the bus and the found duration from setup token to >> ACK of in toke from device is 22ms. > > You haven't said, but I'll assume your control transfer doesn't have a > Data stage. The IN token is sent by the host (not the device) during > the Status stage; in response the device sends a 0-length DATA1 packet, > and then the host (not the device) sends the final ACK. In other > words, neither the ACK nor the IN token comes from the device. > >> I know there might be some sw effort but 75-22= 53ms seems too long >> for bringing back the data from QTD.) > > Assuming the ACK packet you saw really did mark the end of the transfer > then you are right; the URB should complete a few ms later. > > Did you monitor the bus while running a test with a 10-second timeout? > Maybe comparing the results of the two tests will explain why the > timeout occurs. I found there is debugfs I can use to monitor each urb transaction. But I have one question? how could I combine output of dmesg and debugfs together? There is an timeout error message in usb driver and I want to combine dmesg together with urb traffic such that I can find out the urb of timeout happened. appreciate your help, milloody -- 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
