Intel PXA255 Isochronous Transaction Type, Control Transaction Type, Bulk Transaction Formats

USB Device Controller

Table 12-7. 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
	Packets from UDC to host are boldface

12.3.5.2Isochronous Transaction Type

Isochronous transactions ensure constant rate, error-tolerant transmission of data between the host and UDC. The host schedules isochronous packets during every frame. USB protocol allows 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. Two packet types are used to construct isochronous transactions: token and data. The types of isochronous transactions based on data direction are shown in Table 12-8.

Table 12-8. Isochronous Transaction Formats

Action	Token Packet	Data Packet
Host received data from UDC	IN	DATA0
UDC received data from host	OUT	DATA0

Packets from UDC to host are boldface

12.3.5.3Control Transaction Type

The host uses control transactions 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. Control transactions, by default, use DATA0 type transfers. Table 12-9shows the four types of control transactions.

Table 12-9. Control Transaction Formats

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
	Packets from UDC to host are boldface

Intel® PXA255 Processor Developer’s Manual 12-7