Intel IXP400 manual Control Transaction Formats, Set-Up Stage, Interrupt Transaction Formats

Intel® IXP400 Software

Access-Layer Components: USB Access (ixUSB) API

Table 56. Control Transaction Formats, Set-Up Stage

Action	Token Packet	Data Packet	Handshake Packet
UDC successfully received control from host	Setup	DATA0	ACK
UDC temporarily unable to receive data	Setup	DATA0	NAK
UDC endpoint needs host intervention	Setup	DATA0	STALL
UDC detected PID, CRC, or bit stuff error	Setup	DATA0	None

NOTE: Packets from UDC to host are boldface.

Control transfers are assembled by the host by sending a control transaction to tell the UDC what type of control transfer is taking place (control read or control write), followed by two or more bulk data transactions. The first stage of the control transfer is the setup. The device must either respond with an ACK; or if the data is corrupted, it sends no handshake.

The control transaction, by default, uses a DATA0 transfer, and each subsequent bulk data transaction toggles between DATA1 and DATA0 transfers. For a control write to an endpoint, OUT transactions are used. For control reads, IN transactions are used.

The transfer direction of the last bulk data transaction is reversed. It is used to report status and functions as a handshake. The last bulk data transaction always uses a DATA1 transfer by default (even if the previous bulk transaction used DATA1). For a control write, the last transaction is an IN from the UDC to the host, and for a control read, the last transaction is an OUT from the host to the UDC.

Table 57. Control Transaction Formats

Control Write	Setup	DATA (BULK OUT)	STATUS (BULK IN)
Control read	Setup	DATA (BULK IN)*	STATUS (BULK OUT)

NOTE: Packets from UDC to host are boldface.

Interrupt transactions are used by the host 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. Table 58 shows the eight possible types of interrupt transactions.

Table 58. Interrupt Transaction Formats

Action	Token Packet	Data Packet	Handshake Packet
Host successfully received data from UDC	In	DATA0/DATA1	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/DATA1	None
UDC successfully received data from host	Out	DATA0/DATA1	ACK
UDC temporarily unable to receive data	Out	DATA0/DATA1	NAK
UDC endpoint needs host intervention	Out	DATA0/DATA1	STALL
UDC detected PID, CRC, or bit stuff error	Out	DATA0/DATA1	None

NOTE: Packets from UDC to host are boldface.

Programmer’s Guide	IXP400 Software Version 2.0	April 2005
	Document Number: 252539, Revision: 007	301