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164 10/100 Mbps Ethernet Controller Family Open Source Software Developer Manual
82550 and 82551QM Specific Information
— Fragment offset equals 0. This is expected but not checked by hardware.
— IP options are not altered by hardware if they are present.
— IP header checksum is calculated by the checksum hardware if the IP checksum bit is set
in the IPCB.
• TCP header is processed:
— Sequence number is not changed.
— URG, RST, and SYN flags are expected to be clear but are not checked by hardware.
— ACK flag value will be transmitted as in the prototype header.
— Urgent pointer equals 0. This is expected but not checked by hardware.
— If the FIN flag equals 1, then it is cleared in the first frame.
— If the PSH flag equals 1, then it is cleared in the first frame.
— TCP options are not altered by hardware if they are present. TCP options include time
stamp.
— TCP checksum is calculated by checksum hardware if the TCP checksum bit is set in the
IPCB.
B.3.4.3 Intermediate Frames Processing
The number of bytes left for transmission after the first frame is calculated by subtracting the N *
Maximum TCP Payload from the Total TCP/UDP Payload. In other words,
(N * MAX TCP PAYLOAD) – (TOTAL TCP/UDP PAYLOAD)
If the next frame is not the last frame, the number of bytes transmitted is updated and the frame
processing rules below should be followed.
• L2 header should be left intact as in the first frame.
• IP header is processed:
— IP identification is incremented from last value.
— IP options are not altered by hardware if they are present.
— IP header checksum is calculated by checksum hardware if the IP checksum bit is set in
the IPCB.
• TCP header is processed:
— Sequence number is updated for outgoing packets. The previous frame size (TCP payload
only) is added to the previous frame sequence number (modulo 2
32
).
— All flags are left intact as in the first frame.
— Urgent pointer is left intact as in the first frame.
— TCP options are not altered by hardware if they are present
— Pseudo header checksum remains unchanged.
— TCP checksum is calculated by checksum hardware if the TCP checksum bit is set in the
IPCB.