Intel IXP400 manual Bulk Transaction Formats, Isochronous Transaction Formats

Intel® IXP400 Software

Access-Layer Components: USB Access (ixUSB) API

The eight possible types of bulk transactions based on data direction, error, and stall conditions are shown in Table 54. (Packets sent by the UDC to the host are highlighted in boldface type. Packets sent by the host to the UDC are not boldfaced.)

Table 54. Bulk 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.

Isochronous transactions guarantee constant rate, error-tolerant transmission of data between the host and UDC. The host schedules isochronous packets during every frame on the USB, typically 1 ms, 2 ms, or 4 ms.

USB protocol allows for isochronous transfers to take up to 90% of the USB bandwidth. Unlike bulk transactions, if corrupted data is received, the UDC will continue to process the corrupted data that corresponds to the current start of frame indicator.

Isochronous transactions do not support a handshake phase or retry capability. The two packet types used to construct isochronous transactions are token and data. The two possible types of isochronous transactions, based on data direction, are shown in Table 55.

Table 55. Isochronous Transaction Formats

Action	Token Packet	Data Packet
Host successfully received data from UDC	In	DATA0/DATA1
UDC successfully received data from host	Out	DATA0/DATA1
NOTE: Packets from UDC to host are boldface.

Control transactions are used by the host to configure endpoints and query their status. Like bulk transactions, control transactions begin with a setup packet, followed by an optional data packet, then a handshake packet. Note that control transactions, by default, use DATA0 type transfers.

Table 56 shows the four possible types of control transactions.

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