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IXP400 Software
Access-Layer Components: USB Access (ixUSB) API
April 2005 IXP400 Software Version 2.0 Programmer’s Guide
300 Document Number: 252539, Revision: 007
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.)
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
1ms, 2ms, or 4ms.
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.
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.
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.
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.