Intel IXC1100, IXP42X 18.3.6 UDC Device Requests

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 tr ansfers. 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.

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.

Table170 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.