DA82562EM Intel, DA82562EM Datasheet - Page 164

• Manufacturer Part Number: DA82562EM
• Manufacturer: Intel

Specifications of DA82562EM

• Lead Free Status / Rohs Status: Not Compliant

82550 and 82551 Specific Information
B.2
B.2.1
156
Table 70. IPCB Structure Checksum Offload
Note: IP fragmentation is not supported by the 82550. Therefore, the driver should not request any
Note: The 82550 is capable of computing one level of IP header and one TCP/UDP header and payload.
Note: Per RFC768, if the computed UDP checksum is zero, it is transmitted as all ones. A UDP
modes of operation. For instance, the driver must guarantee proper values for the Maximum TCP
Payload in Large Send mode and VLAN length inclusion.
offload features for an IP fragment.
82550 Checksum Operation
The 82550 hardware supports an IP header (including options), UDP and TCP checksum
computation. The 82550 computes the checksum using two’s complement addition, and therefore
performs end around carry. In other words, it adds the carry generated from bit 15 to the least
significant bit in checksum computation.
In case of multiple IP headers, the driver should compute all except but the outer most IP header
checksum.
checksum transmitted as all zeros means that the transmitter generated no UDP checksum.
Driver Interface
Software should compute the partial checksum of the pseudo header and store it in the checksum
field of the TCP or UDP header. The partial checksum is the 16-bit one’s complement sum of the 6
words in the pseudo header. It is not the one’s complement of the one’s complement sum. If this is
not done by the stack, the driver must be aware of the IP header offset and base offset and the
length of the TCP segment to compute and store the pseudo header checksum.
The IPCB structure used for the checksum offload is presented below. The fields relevant to
checksum operation are shaded.
E
L
TCP Header Offset (8 bits)
S
TBD Number
I
IP Activation (12 bits)
10/100 Mbps Ethernet Controller Family Open Source Software Developer Manual
CID (5 bits)
Total TCP Payload (16 bits)
Odd Word (D31:D16)
Maximum TCP Payload
IP Header Offset (8 bits)
000
Transmit Threshold
N
C
Transmit Buffer #0 Address (32 bits)
CMD (4 bits)
TBD Array Address (32 bits)
Link Address (32 bits)
Reserved (32 bits)
C X
E
O
F
E
L
0
0
O
K U
Scheduling (20 bits)
Even Word (D15:D0)
Transmit Buffer #0 Size (14 bits)
IPCB Byte Count (14 bits)
VLAN (16 bits)
XXXX XXXX XXXX (12 bits)
Reserved (14 bits)
Offset
1Ch
10h
14h
18h
Ch
0h
4h
8h