CX82100 Home Network Processor Data Sheet
8.2
USB Data Flow
USB data can be identified as control, bulk, or interrupt data in the HNP.
Control data is usually structured as a command phase initiated by the USB host,
followed by data either provided by the device (IN), i.e., HNP (IN), or sent to it by the
host (OUT), followed in turn by a status phase which serves as an acknowledgement of
transfer. Control transfers are directed to Endpoint 0, and requires no device
configuration, i.e., control transfers can be active from the moment of device attachment.
All other transfers require device configuration and setting of the appropriate device
address by the host to be accepted by the HNP. In another words, a process called
enumeration is must be initiated by the host every time the HNP is connected. Control
data flow through Endpoint 0 must be USB Specification Rev. 1.1 Chapter 9 compliant
and other USB stack command aware. Packet size for Endpoint 0 is 64 bytes for control
data and 8 bytes for control command.
Bulk transfers are simple data transfers with ACK/NAK token exchange between the host
and the HNP to signal the completion of the transfer. Again, these transfers are started by
the host sending a IN (OUT) token to the HNP, which responds within a timeout period
with data and/or ACK/NAK (depending on the direction of transfer) to keep the host
from retrying to transfer the data. The packet size for bulk transfers is always less than or
equal to 64 bytes.
Interrupt data is infrequent data that flows only from the HNP to the host and is a result
of the host polling the HNP periodically. The HNP Interrupt Endpoint is fixed at IN type
with 8 bytes per packet.
101306C
Conexant Proprietary and Confidential Information
8-5
CONEXANT [ CONEXANT SYSTEMS, INC ]
