User Guide

66 Hardware Reference Manual
Intel
®
IXP2800 Network Processor
Technical Description
All elements within a TBUF partition are transmitted in the order. Control information associated
with the element defines which bytes are valid. The data from the TBUF will be shifted and byte
aligned as required to be transmitted.
2.7.4.1.1 SPI-4 and TBUF
For SPI-4, data is put into the data portion of the element, and information for the SPI-4 Control
Word that will precede the data is put into the Element Control Word.
When the Element Control Word is written, the information is:
The definitions of the fields are shown in Table 15.
3
1
3
0
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
1
9
1
8
1
7
1
6
1
5
1
4
1
3
1
2
1
1
1
0
9876543210
Payload Length
Prepend
Offset
Prepend Length
Payload
Offset
Res
Skip
Res
SOP EOP
ADR
6
3
6
2
6
1
6
0
5
9
5
8
5
7
5
6
5
5
5
4
5
3
5
2
5
1
5
0
4
9
4
8
4
7
4
6
4
5
4
4
4
3
4
2
4
1
4
0
3
9
3
8
3
7
3
6
3
5
3
4
3
3
3
2
Res
Table 15. TBUF SPI-4 Control Definition
Field Definition
Payload Length
Indicates the number of Payload bytes, from 1 to 256, in the element. The value of 0x00
means 256 bytes. The sum of Prepend Length and Payload Length will be sent. That
value will also control the EOPS field (1 or 2 bytes valid indicated) of the Control Word
that will succeed the data transfer. Note 1.
Prepend Offset Indicates the first valid byte of Prepend, from 0 to 7
Prepend Length Indicates the number of bytes in Prepend, from 0 to 31.
Payload Offset Indicates the first valid byte of Payload, from 0 to 7.
Skip
Allows software to allocate a TBUF element and then not transmit any data from it.
0—transmit data according to other fields of Control Word.
1—free the element without transmitting any data.
SOP
Indicates if the element is the start of a packet. This field will be sent in the SOPC field of
the Control Word that will precede the data transfer.
EOP
Indicates if the element is the end of a packet. This field will be sent in the EOPS field of
the Control Word that will succeed the data transfer. Note 1.
ADR
The port number to which the data is directed. This field will be sent in the ADR field of the
Control Word that will precede the data transfer.
NOTE:
1. Normally EOPS is sent on the next Control Word (along with ADR and SOP) to start the next element. If
there is no valid element pending at the end of sending the data, the transmit logic will insert an Idle Control
Word with the EOPS information.