Specifications

USB Transfers—Actual Control Transfer

 Control Transfer Read Example — GET_STATUS command from Host

Transfer

Transaction

Packet

Hierarchy

SETUP Phase

DATA Phase

Status Phase

0 length field

Here is an actual USB analyzer capture of data traffic for a control transfer. This is a

control transfer (Get_Status) that a host has sent out to a device. Keeping in mind

our packet formats we can see the token packet identifies the first transaction as the

setup providing us with the device address and endpoint information. The second

transaction is the data phase using the address and endpoint and then the device

adds the data requested. The final transaction is the status phase using a 0-length

data packet to signify that the transfer completed successfully.

Note: Not all USB tools provide the data in the same format.