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Intel
®
IXP42X Product Line of Network Processors and IXC1100 Control Plane Processor
September 2006 DM
Order Number: 252480-006US 477
Universal Serial Bus (USB) v1.1 Device Controller—Intel
®
IXP42X product line and IXC1100
control plane processors
To assemble control transfers, the host sends a control transaction to tell the UDC what
type of control transfer is taking place (control read or control write), followed by one
or more data transactions. The setup is the first stage of the control transfer. The
device must respond with an ACK or no handshake (if the data is corrupted).
The control transaction, by default, uses a DATA0 transfer and each subsequent data
transaction toggles between DATA1 and DATA0 transfers. A control write to an endpoint
uses OUT transactions.
Control reads use IN transactions. The transfer direction is the opposite of the last data
transaction. The transfer direction is used to report status and functions as a
handshake.
For a control write, the last transaction is an IN from the UDC to the host. For a control
read, the last transaction is an OUT from the host to the UDC. The last data transaction
always uses a DATA1 transfer, even if the previous transaction used DATA1.
18.3.5.4 Interrupt Transaction Type
The host uses interrupt transactions to query the status of the device. Like bulk
transactions, interrupt transactions begin with a setup packet, followed by an optional
data packet, then a handshake packet. Interrupt transactions, by default, use DATA0
type transfers.
Table 170 shows the four types of interrupt transactions.
18.3.6 UDC Device Requests
The UDC uses its control, status, and data registers to control and monitor the transmit
and receive FIFOs for endpoints 1 - 15. The host controls all other UDC configuration
and status reporting using device requests that are sent as control transactions to
endpoint 0 via the USB.
Each setup packet to Endpoint 0 is 8 bytes long and specifies:
• Data transfer direction: host to device, device to host
• Data transfer type:
—Standard
—Class
—Vendor
• Data recipient:
—Device
—Interface
—Endpoint
—Other
Table 170. Interrupt Transaction Formats
Action Token Packet Data Packet
†
Handshake Packet
†
Host successfully received data from UDC IN DATA0 ACK
UDC temporarily unable to transmit data IN
None NAK
UDC endpoint needs host intervention IN
None STALL
Host detected PID, CRC, or bit stuff error IN DATA0
None
† Packets from UDC to host are boldfaced.