MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
14-46
Freescale Semiconductor
14.4.14.1 Transmission Errors
14.4.14.1.1 Transmitter Underrun
If this error occurs, the FEC sends 32 bits that ensure a CRC error and stops transmitting. All remaining
buffers for that frame are then flushed and closed. The UN bit is set in the EIR. The FEC will then continue
to the next transmit buffer descriptor and begin transmitting the next frame.
The “UN” interrupt will be asserted if enabled in the EIMR register.
14.4.14.1.2 Retransmission Attempts Limit Expired
When this error occurs, the FEC terminates transmission. All remaining buffers for that frame are flushed
and closed, and the RL bit is set in the EIR. The FEC will then continue to the next transmit buffer
descriptor and begin transmitting the next frame.
The “RL” interrupt will be asserted if enabled in the EIMR register.
14.4.14.1.3 Late Collision
When a collision occurs after the slot time (512 bits starting at the preamble), the FEC terminates
transmission. All remaining buffers for that frame are flushed and closed, and the LC bit is set in the EIR
register. The FEC will then continue to the next transmit buffer descriptor and begin transmitting the next
frame.
The “LC” interrupt will be asserted if enabled in the EIMR register.
14.4.14.1.4 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 4 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 still seems to be functioning properly. This
is called the heartbeat condition.
If the HBC bit is set in the TCR register and the heartbeat condition is not detected by the FEC after a frame
transmission, then a heartbeat error occurs. When this error occurs, the FEC closes the buffer, sets the HB
bit in the EIR register, and generates the HBERR interrupt if it is enabled.
14.4.14.2 Reception Errors
14.4.14.2.1 Overrun Error
If the receive block has data to put into the receive FIFO and the receive FIFO is full, the FEC sets the OV
bit in the RxBD. All subsequent data in the frame will be 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. This frame must be discarded by
the driver.
14.4.14.2.2 Non-Octet Error (Dribbling Bits)
The Ethernet controller handles 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,
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