Hi, I have been analyzing USB traffic with USB 2.0 protocol analyzer. In my test setup I have a Full-Speed USB serial device connected to High-Speed hub which is connected to Linux host. The protocol analyzer is connected between the Linux host and the High-Speed hub. The test case which I have been analyzing opens the serial device, writes a few bytes to the device and closes the device. The USB serial device has a bulk IN endpoint and a bulk OUT endpoint for data transfer. When the device node of the USB serial device is closed from user space, I can see that usually the last transaction to the bulk IN endpoint of the USB serial device is a start-split transaction without a corresponding complete-split transaction. Sometimes the split transaction is completed with the corresponding complete-split but most often not. The transaction translator buffer of the High-Speed hub is always cleared with ClearTTBuffer request regardless if the split transaction was completed or not. I have tested this case with a USB to serial converter (pl2303) using pl2303 driver and usbserial_generic driver. I also used USB CDC device with cdc_acm driver. The results are the same with every case. My question is that why is ClearTTBuffer request always used in this case? According to the USB 2.0 specification paragraph 11.17.5 (on page 372), ClearTTBuffer should be used as a part of endpoint halt processing when split transactions have failed. Wouldn't it be better to always complete the started split transaction instead of always send ClearTTBuffer request? Thanks, Antti Pulakka -- 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
