PMC-Sierra, Inc.
PRELIMINARY
PM5381 S/UNI-2488
DATASHEET
PMC-2000489
ISSUE 1
SATURN USER NETWORK INTERFACE FOR 2488 MBIT/S
Table 3: Byte Destuffing
Original
Escaped
7D-5E
7E (Flag Sequence)
7D (Control Escape)
Aborted Packet
7D-5D
7D-7E
10.7.9 POS FCS Check
The FCS Generator performs a CRC-CCITT or CRC-32 calculation on the whole POS frame,
after byte destuffing and data descrambling scrambling. A parallel implementation of the CRC
polynomial is used. The CRC algorithm for the frame checking sequence (FCS) field is either a
CRC-CCITT or CRC-32 function. The CRC-CCITT is two bytes in size and has a generating
5
12
16
polynomial g(X) = 1 + X + X + X . The CRC-32 is four bytes in size and has a generating
2
4
5
7
8
10
11
12
16
22
23
26
polynomial g(X) = 1 + X + X + X + X + X + X + X + X + X + X + X + X + X
32
+ X . The first FCS bit transmitted is the coefficient of the highest term. . Packets with FCS
errors are marked as such and should be discarded by the system.
Figure 14: CRC Decoder
g1
g2
gn-1
D0
D1
Dn-1
. . .
+
+
+
+
Message
10.7.10 POS Performance Monitor
The Performance Monitor consists of four 16-bit saturating error event counters, one 32-bit
saturating received good packet counter, and one 40-bit counter for accumulating packet bytes.
One of the error event counters accumulates FCS errors. The second error event counter
accumulates minimum length violation packets. The third error event counter accumulates
maximum length violation packets. The fourth error event counter accumulates aborted packets.
The 32-bit receive good packet counter counts all error free packets.
Each counter may be read through the microprocessor interface. Circuitry is provided to latch
these counters so that their values can be read while simultaneously resetting the internal
counters to 0 or 1, whichever is appropriate, so that a new period of accumulation can begin
without loss of any events. The counters should be polled at least once per second so error
events will not be missed.
Proprietary and Confidentail to PMC-Sierra Inc., and for its Customer’s Internal Use
69
PMC [ PMC-SIERRA, INC ]
