RE: Bulk and Interrupt IN Transaction Sequence

ryan_g — Mon, 23 Jul 2018 16:46:06 GMT

Thank you Håkon, this was helpful and clears up my confusion surrounding the documentation.

RE: Bulk and Interrupt IN Transaction Sequence

Håkon Alseth — Mon, 23 Jul 2018 10:00:35 GMT

Hi,

I haven't used wireshark for USB sniffing, so I cannot comment much on what it shows and how "deep" it goes given that it needs to wrap around the OS in order to sniff the packets.

I use a dedicated usb sniffer (ellisys usb explorer).

If using "interrupt" transfer, your host will poll the usb device based on the bInterval set in the descriptor (see this site for details, search for bInterval).

If using BULK type transfer (which the data transfer for CDC is), then your device is polled based on the USB Hosts availability.

Here's a typical IN transfer (IN, DATA0 returned, ACK) where the device sends data to the USB Host:

This is also covered in the packet types of USB: https://www.beyondlogic.org/usbnutshell/usb3.shtml#USBPacketTypes

Kind regards,

Håkon