Fast Ethernet Controller (FEC)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
45-8
Freescale Semiconductor
The effectiveness of the hash table declines as the number of addresses increases.
The user must initialize the hash table registers. The FEC does not support the
SET
GROUP
ADDRESS
command, which can be used in CPM Ethernet controllers. The user may compute the hash for a particular
address in software or use the
SET
GROUP
ADDRESS
command in an off-line CPM channel, retrieve the
result, and use it to program the FEC hash table registers. The CRC32 polynomial to use in computing the
hash is as follows:
45.2.7
Inter-Packet Gap Time
The minimum inter-packet gap time for back-to-back transmission is 96 bit times. After completing a
transmission or after the backoff algorithm completes, the transmitter waits for the carrier sense signal
(CRS) to be negated before starting its 96 bit time IPG counter. Frame transmission may begin 96 bit times
after CRS is negated if it stays negated for at least 60 bit times. If CRS asserts during the last 36 bit times,
it is ignored and a collision occurs.
The receiver receives back-to-back frames with a minimum spacing of at least 28 bit times. If an
interrupted gap between receive frames is less than 28 bit times, the receiver may discard the next frame.
45.2.8
Collision Handling
If a collision occurs during frame transmission, the FEC continues transmitting for at least 32 bit times,
sending a JAM pattern of 32 ones. If the collision occurs during the preamble sequence, the JAM pattern
is sent after the preamble sequence.
If a collision occurs within 64 byte times, the retry process is initiated. The transmitter waits a random
number of slot times. A slot time is 512 bit times. If a collision occurs after 64 byte times, no
retransmission is performed and the end of frame buffer is closed with an LC error indication.
45.2.9
Internal and External Loopback
The FEC supports both internal and external loopback. In loopback mode, both FIFOs are used and the
FEC operates in full-duplex fashion. Both internal and external loopback are configured through
R_CNTRL[LOOP, DRT].
For internal loopback, set LOOP = 1 and DRT = 0. TX_EN and TX_ER are not asserted during internal
loopback.
For external loopback, set LOOP = 0 and DRT = 0. Configure the external transceiver for loopback.
45.2.10 Ethernet Error-Handling Procedure
The FEC reports frame reception and transmission error conditions using the FEC BDs and the I_EVENT
register.
X
32
X
26
X
23
X
22
X
16
X
12
X
11
X
10
X
8
X
7
X
5
X
4
X
2
X
1
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Summary of Contents for PowerQUICC MPC870
Page 98: ...MPC885 PowerQUICC Family Reference Manual Rev 2 I 4 Freescale Semiconductor ...
Page 118: ...MPC885 Overview MPC885 PowerQUICC Family Reference Manual Rev 2 1 20 Freescale Semiconductor ...
Page 158: ...The MPC8xx Core MPC885 PowerQUICC Family Reference Manual Rev 2 3 18 Freescale Semiconductor ...
Page 288: ...MPC885 PowerQUICC Family Reference Manual Rev 2 III 4 Freescale Semiconductor ...
Page 554: ...MPC885 PowerQUICC Family Reference Manual Rev 2 V 6 Freescale Semiconductor ...
Page 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
Page 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
Page 1336: ...MPC885 PowerQUICC Family Reference Manual Rev 2 D 16 Freescale Semiconductor ...
Page 1358: ...MPC885 PowerQUICC Family Reference Manual Rev 2 D 38 Freescale Semiconductor ...
Page 1370: ...MPC880 MPC885 PowerQUICC Family Reference Manual Rev 2 E 4 Freescale Semiconductor ...
Page 1386: ...Revision History MPC885 PowerQUICC Family Reference Manual Rev 2 I 2 Freescale Semiconductor ...