When an error is detected this will be flagged and the corrupt packet will be discarded. The packets are buffers which are called endpoints.ĬRC is applied to the packets to maintain data integrity. Then the controller will detect the USB packet start (start with a synac field). When the signal is received the NRZI is decoded and bitstuffing removed. The clocks are generated from the data signal. Adding this dummy bit is called bit-stuffing and is used to keep the clocks of the host and client in sync. If a 6bits of 1 are sended an additional 7th bit (0) is send to make the signal flip. A 0 will make the signal flip sign and a 1 will keep the same signal level. Oh, and don't forget, you'd need software on your computer do do something usefull with the captured data. So if you'd want to build a sniffer of your own, you'd be looking at a differential data buffer capable of at least 480Mb/s, and some processor to handle the copy of the data and store it in memory, then have your computer C download the captured data. If you build a sniffer, then yes, but not with the simple splitter-cable you have in mind.Īlso note that USB3 is finally bi-directional (where as previous versions where not).Īlso note that USB2 is already 480Mb/s and this might (depending on your computer C) be a lot or impossible to capture as a stream. Will I be able to read the data off the USB port in C?

Especially since your sniffer MUST run in 'promiscuous mode'. the diodes are useless for your application. Yes, unless your sniffer runs on the host-supplied powerĬan I place a diode on the D+ or D- wires of the sniffing cable of to make the data flow only one-way?ĭ+ and D- are differential data (the base-voltage-levels indicate to the usb-device the maximum amount of current it may draw). What usb-versions do you want to support (specifically, do you need usb3)?Ĭan I disconnect the VCC and GND wires on the sniffing cable, so that C will not try to control B?

Usb traffic sniffer