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• Token
• Handshake
A PRE (Preamble) PID precedes a low-speed (1.5 Mbps) USB transmission. The UDC
supports high-speed (12 Mbps) USB transfers only. PRE packets that signify low-speed
devices and the low-speed data transfer that follows such PRE packets are ignored.
8.3.4.1
Token Packet Type
A token packet is placed at the beginning of a frame and is used to identify OUT, IN,
SOF, and SETUP transactions. OUT and IN frames are used to transfer data, SOF
packets are used to time isochronous transactions, and SETUP packets are used for
control transfers to configure endpoints.
A Token packet consists of a sync, a PID, an address, an endpoint, and a CRC5 field
(see
Table
used to select the UDC endpoint that receives the data. For an IN transaction, the
address and endpoint fields are used to select the UDC endpoint that transmits data.
Table 110.
IN, OUT, and SETUP Token Packet Format
8 Bits
Sync
8.3.4.2
Start-of-Frame Packet Type
A Start-of-Frame (SOF) packet is a special type of token packet that is issued by the
USB host at a nominal interval of once every 1 ms +/- 0.0005 ms.
SOF packets consist of a sync, a PID, a frame number (which is incremented after each
frame is transmitted), and a CRC5 field, as shown in
packets every 1 ms prevents the UDC from going into suspend mode.
Table 111.
SOF Token Packet Format
8 Bits
Sync
8.3.4.3
Data Packet Type
Data packets follow token packets and are used to transmit data between the USB host
and UDC. There are two types of data packets as specified by the PID: DATA0 and
DATA1. These two types of Data Packets are used to provide a mechanism to guarantee
data sequence synchronization between the transmitter and receiver across multiple
transactions.
During the handshake phase, the transmitter and receiver determine which data token
type to transmit first. For each subsequent packet transmitted, the data packet type is
toggled (DATA0, DATA1, DATA0, and so on).
A data packet consists of a sync; a PID; from 0 to 1,023 bytes of data; and a CRC16
field, as shown in
for an Interrupt IN data payload, a maximum of 64 bytes of data for a bulk data
payload and a maximum of 256 bytes of data for an isochronous data payload.
®
®
Intel
IXP45X and Intel
IXP46X Product Line of Network Processors
Developer's Manual
284
®
®
Intel
IXP45X and Intel
• Data
• Special
110). For OUT and SETUP transactions, the address and endpoint fields are
8 Bits
PID
Address
8 Bits
PID
Frame Number
Table
112. Note that the UDC supports a maximum of 8 bytes of data
IXP46X Product Line of Network Processors—USB 1.1 Device
7 Bits
4 Bits
Endpoint
Table
11 Bits
5 Bits
CRC5
Controller
5 Bits
CRC5
111. The presence of SOF
August 2006
Order Number: 306262-004US
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