Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 770

SCC Ethernet Mode
In external loopback operation, the ethernet controller listens for data being received from the EEST at the
same time that it is sending.
27.15 Full-Duplex Ethernet Support
To run full-duplex ethernet, select loopback and full-duplex ethernet modes in the SCC's protocol-specific
mode register, (PSMR[LPB, FDE] = 1). The loopback mode tells the ethernet controller to accept received
frames without signaling a collision. Setting PSMR[FDE] tells the controller that it can send while
receiving without waiting for a clear line (carrier sense).
27.16 Handling Errors in the Ethernet Controller
The ethernet controller reports frame reception and transmission error conditions using channel BDs, error
counters, and SCCE. Table 27-5
Error
Transmitter If this error occurs, the channel sends 32 bits that ensures a CRC error, stops sending the buffer,
underrun closes it, sets the UN bit in the TxBD and SCCE[TXE]. The channel resumes transmission after it
receives a
Carrier sense When this error occurs and no collision is found in the frame, the channel sets the CSL bit in the
lost during frame TxBD, sets SCCE[TXE], and continues sending the buffer normally. No retries are performed after
transmission this error occurs. Carrier sense is the logical OR of RENA and CLSN.
Retransmission The channel stops sending the buffer, closes it, sets the RL bit in the TxBD and SCCE[TXE]. The
retry limit channel resumes transmission after it receives a
expired
Late collision When this error occurs, the channel stops sending the buffer, closes it, sets SCCE[TXE] and the LC
bit in the TxBD. The channel resumes transmission after it receives the
command. This error is discussed further in the definition of PSMR[LCW].
Heartbeat Some transceivers have a heartbeat (signal-quality error) self-test. To signify a good self-test, the
transceiver indicates a collision to the MPC885 within 20 clocks after the ethernet controller sends
a frame. This heartbeat condition does not imply a collision error, but that the transceiver seems to
be functioning properly. If SCCE[HBC] = 1 and the MPC885 does not detect a heartbeat condition
after sending a frame, a heartbeat error occurs; the channel closes the buffer, sets the HB bit in the
TxBD, and generates the TXE interrupt if it is enabled.
Table 27-5 describes reception errors.
Error
Overrun The ethernet controller maintains an internal FIFO for receiving data. When it overruns, the channel
writes the received byte over the previously received byte. The previous byte and frame status are
lost. The channel closes the buffer, sets RxBD[OV] and SCCE[RXF], and increments the discarded
frame counter (DISFC). The receiver then enters hunt mode.
Busy A frame was received and discarded because of a lack of buffers. The channel sets SCCE[BSY] and
increments DISFC. The receiver then enters hunt mode.
27-14
describes transmission errors.
Table 27-5. Transmission Errors
command.
RESTART TRANSMIT
Table 27-6. Reception Errors
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Description
command.
RESTART TRANSMIT
RESTART TRANSMIT
Description
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