Intel 82559 用户手册

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Note: Using software parsing is only allowed with legal TCP/IP or UDP/IP packets. When software 

parsing is used, IP and TCP offsets in the IPCB must point to the appropriate headers and the total 

TCP/UDP payload should be specified. For all other datagrams, hardware parsing must be used.

Note: VLAN tagging (either in memory or by hardware) and SNAP headers are allowed when software 

parsing is used as long as the above guideline is met. IP and TCP header offsets are calculated 
according to memory data structures. For example, if VLAN tag is inserted by hardware, offsets do 

not change.

The IPCB byte count specifies the number of bytes of transmit data in the immediate data area 

(from offset 20h and on).

When the Large Send mode is selected, this field is interpreted as the Maximum TCP Payload. 

Otherwise, this 16-bit field is interpreted as the TBD number and Transmit Threshold. The TBD 
number specifies the total number of TBDs associated with this IPCB. The Transmit Threshold is 

defined in 

 above.

Note: A mode bit puts the 82550 and 82551 into a specific mode. When the mode bit is clear, all 

parameters that relate to that mode are ignored by the device hardware. Mode bits should obey 

consistency rules since not all combinations are allowed. The result of a non-supported 

combination is unpredictable.

Note: It is driver responsibility to guarantee that the total length of a frame is not larger than the allowed 

MTU size for that connection (which is dependent upon the IP address pair). This is relevant in all 

Scheduling

12h:
10h

19:0

Parameter

If the Scheduled Send bit is set, the transmission of the frame 
associated with the IPCB is delayed until the internal 
scheduling counter of the controller reaches the scheduling 
value.
Bits 16:0 are the time stamp and bits 19:17 may be used to 
specify time window.

Maximum TCP 
Payload

Fh:Eh 15:0

Parameter

This field specifies the maximum number of bytes to be 
transmitted in the TCP payload of an Ethernet frame that is 
part of the Large Send. All frames use this size except the last 
one. This field is ignored when the Large Send bit is clear.

Transmit 
Threshold

Eh

7:0

Parameter

In units of 8 bytes, this field defines the number of bytes that 
should be present in the Transmit FIFO before transmission 
starts. It is relevant only if the checksum requires the whole 
frame to be in Transmit FIFO. The value of this parameter 
should be in the range of 1h to E0h.