[tcpdump-workers] Link-Layer Header Type request: USB 2.0

Tomasz Moń desowin at gmail.com
Sun Jul 21 15:40:39 EDT 2019


Hello,

I would like to request a Link-Layer Header Type for USB 2.0 packets.
This is intended to be used as a export format from sigrok.

While sigrok contains code to convert D+/D- signals into
LINKTYPE_USB_LINUX_MMAPPED, it is a bit limited. One issue is that
without dissecting USB Configuration Descriptor, it is impossible to
determine endpoint type for non-split transactions. Another issue that
without knowing endpoint maximum transfer size (also found in
Configuration Descriptor), it is not possible to accurately determine
short transfers and thus convert multiple transactions into transfer.
If the user is not familiar with these limitations it can be really
confusing.

I am currently working on OpenVizsla dissector for Wireshark. While
LINKTYPE_OPENVIZSLA packets can contain USB 2.0 packets, they also do
contain information that is specific to the OpenVizsla itself. The
dissector code I have written so far clearly separates OpenVizsla from
USB Link-Layer and thus I believe it makes sense to have a separate
direct entry point for USB 2.0 packets.

The new Link-Layer Header Type is supposed to contain the USB 2.0
packets. That is, anything that appears on the bus between the Start-
and End-of-Packet delimiters. The packet format is described in
Chapter 8 Protocol Layer of Universal Serial Bus Specification
Revision 2.0.

Best Regards,
Tomasz Moń


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