Packet Formats; Endpoint Field Addressing - Intel IXP45X Developer's Manual

USB 1.1 Device Controller—Intel
Processors
The host is then responsible for assigning a unique address to each device on the bus.
Addresses are assigned in the enumeration process, one device at a time. After the
host assigns the an address to the UDC, the UDC only responds to transactions directed
to that address. The Address field follows the PID in every packet transmitted.
When the UDC detects a packet that is addressed to it, it uses the Endpoint field to
determine which of the UDC's endpoints is being addressed. The Endpoint field contains
four bits. Encodings for endpoints 0 (0000b) through 15 (1111b) are allowed. The
Endpoint field follows the Address field.
endpoint field.
Table 109.

Endpoint Field Addressing

Endpoint Field Value
The Frame Number is an 11-bit field incremented by the host each time a frame is
transmitted. When it reaches its maximum value (2,047 [0x7FF]) its value rolls over.
Frame Number is transmitted in the SOF packet, which the host outputs in 1-ms
intervals.
Device controllers use the Frame Number field to control isochronous transfers. Data
fields are used to transmit the packet data between the host and the UDC. A data field
consists of 0 to 1,023 bytes. Each byte is transmitted least-significant-bit-first. The
UDC generates an interrupt to indicate that a Start of Frame event has occurred.
CRC fields are used to detect errors introduced during token and data-packet
transmission and are applied to all the fields in the packet except the PID field. The PID
contains its own 4-bit 1s complement check field for error detection. Token packets use
a 5-bit CRC (x
16 15
(x +x
of each packet.
8.3.4

Packet Formats

USB supports four packet types:
August 2006
Order Number: 306262--, Revision: 004US
® ®
IXP45X and Intel
UDC Endpoint Selected
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
5 2
+x +1) called CRC5 and Data packets use a 16-bit CRC
2
+x +1) called CRC16. For both CRCs, the checker resets to all 1s at the start
IXP46X Product Line of Network
Table 109 shows the valid values for the
Endpoint 0
Endpoint 1
Endpoint 2
Endpoint 3
Endpoint 4
Endpoint 5
Endpoint 6
Endpoint 7
Endpoint 8
Endpoint 9
Endpoint 10
Endpoint 11
Endpoint 12
Endpoint 13
Endpoint 14
Endpoint 15
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Intel IXP45X and Intel IXP46X Product Line of Network Processors
Developer's Manual
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