STMicroelectronics SPC572L series Reference Manual page 1358

Fast Ethernet Controller (FEC)
EIR[LC] is set. The FEC then continues to the next transmit buffer descriptor and begins
transmitting the next frame. The LC interrupt is asserted if enabled in the EIMR register.
48.5.19.1.4 Heartbeat
Some transceivers have a self-test feature called heartbeat or signal quality error. To signify
a good self-test, the transceiver indicates a collision to the FEC within four microseconds
after completion of a frame transmitted by the Ethernet controller. This indication of a
collision does not imply a real collision error on the network, but is rather an indication that
the transceiver continues to function properly. This is the heartbeat condition.
If TCR[HBC] is set and the heartbeat condition is not detected by the FEC after a frame
transmission, a heartbeat error occurs. When this error occurs, the FEC closes the buffer,
sets EIR[HB], and generates the HBERR interrupt if it is enabled.
48.5.19.2 Reception errors
48.5.19.2.1 Overrun error
If the receive block has data to put into the receive FIFO and the receive FIFO is full, FEC
sets RxBD[OV]. All subsequent data in the frame is discarded and subsequent frames may
also be discarded until the receive FIFO is serviced by the DMA and space is made
available. At this point the receive frame/status word is written into the FIFO with the OV bit
set. The driver must discard this frame.
48.5.19.2.2 Non-octet error (dribbling bits)
The Ethernet controller manages up to seven dribbling bits when the receive frame
terminates past an non-octet aligned boundary. Dribbling bits are not used in the CRC
calculation. If there is a CRC error, the frame non-octet aligned (NO) error is reported in the
RxBD. If there is no CRC error, no error is reported.
48.5.19.2.3 CRC error
When a CRC error occurs with no dribble bits, FEC closes the buffer and sets RxBD[CR].
CRC checking cannot be disabled, but the CRC error can be ignored if checking is not
required.
48.5.19.2.4 Frame length violation
When the receive frame length exceeds MAX_FL bytes the BABR interrupt is generated,
and RxBD[LG] is set. The frame is not truncated unless the frame length exceeds 2047
bytes.
48.5.19.2.5 Truncation
When the receive frame length exceeds 2047 bytes, frame is truncated and RxBD[TR] is
set.
1358/2058 DocID027809 Rev 4
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