K60P100M100SF2RM Datasheet, PDF (1201/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

44.4.8.3.2 Transmit Processing
Chapter 44 10/100-Mbps Ethernet MAC (ENET)
When ENETn_TACC[SHIFT16] is set, the first two bytes of the first word written (bits
15–0) are discarded immediately by the FIFO write logic.
The SHIFT16 bit can be enabled/disabled for each frame individually if required, but can
be changed only between frames.
44.4.8.4 Received Frame Discard
As the receive FIFO must be operated in store and forward mode (ENETn_RSFL
cleared), received frames can be discarded based on the following errors:
• The MAC function receives the frame with an error:
• The frame has an invalid payload length
• Frame length is greater than MAX_FL
• Frame received with a CRC-32 error
• Frame truncated due to receive FIFO overflow
• Frame is corrupted as PHY signaled an error (MII_RX_ERR asserted during
reception)
• An IP frame is detected and the IP header checksum is wrong
• An IP frame with a valid IP header and a valid IP header checksum is detected, the
protocol is known but the protocol specific checksum is wrong
If one of the errors occurs and the IP accelerator function is configured to discard frames
(ENETn_RACC), the frame is automatically discarded. Statistics are maintained
normally and are not affected by this discard function.
44.4.8.5 IPv4 Fragments
When an IP (IPv4) fragment frame is received only the IP header is inspected and its
checksum verified. 32-bit alignment operates on fragments as on normal IP frames, as
specified above.
The IP fragment frame payload is not inspected for any protocol headers. As such, a
protocol header would only exist in the very first fragment. To assist in protocol-specific
checksum verification, the one's-complement sum is calculated on the IP payload (all
bytes following the IP header) and provided with the frame status word.
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
1201