Decoding FEC Errors

Last Updated : Feb 26, 2020 |
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This section describes about decoding the Fast Ethernet Controller (FEC) receiver error (PRN) statements that appear in the log. These Fast Ethernet Controller error messages are shown when the System/Print option is enabled.
For example: PRN: IP403_FEC::ReceiverError 844
The message format is: PRN: PLATFORM_FEC::ReceiverError ABCD
Where:
  • PRN: Indicates that message was output as the result of having the System/Print option enabled.
  • PLATFORM: Indicates the type of system control unit reporting the error. The possible values are IP401NG (Small Office Edition), IP403, IP406, IP406V2 (shows as IP405 in Version 2.1(27)) and IP412.
  • ABCD: This is the actual error code. It is a decode of the Ethernet Receive Buffer Descriptor packet. Note that if the most significant byte (A) is 0 (zero) it is not printed and the error code is only three characters long ( BCD).
FEC: ReceiverError Codes are derived from the Ethernet Receive Buffer Descriptor (RxBD). The table shows the bits within the RxBD that are used to generate the error codes. The N/U labeled options are not used in the FEC error decoding mechanism although they may be non zero.
Byte
Bit
Value
Option
Description
A
0
8
N/U
May be non-zero but not used for FEC decode.
1
4
N/U
2
2
N/U
3
1
N/U
B
4
8
L
Last in frame.
  • 0: The buffer is not the last in the frame.
  • 1: The buffer is the last in the frame.
5
4
0
Always zero
6
2
0
Always zero
7
1
N/U
May be non-zero but not used for FEC decode.
C
8
8
N/U
May be non-zero but not used for FEC decode.
9
4
N/U
10
2
LG
Length Error: Rx frame length violation. The frame length exceeds the value of MAX_FRAME_LENGTH in the bytes. The hardware truncates frames exceeding 2047 bytes so as not to overflow receive buffers This bit is valid only if the L bit is set to 1.
11
1
NO
Non-Octet: A frame that contained a number of bits not divisible by 8 was received and the CRC check that occurred at the preceding byte boundary generated an error. NO is valid only if the L bit is set and CR bit is not set.
D
12
8
SH
Short Frame: A frame length that was less than the minimum defined for this channel was recognized.
13
4
CR
CRC Error: This frame contains a CRC error and is an integral number of octets in length. This bit is valid only if the L bit is set.
14
2
OV
Overrun Error: A receive FIFO overrun occurred during frame reception. If OV is set to 1, the other status bits, LG, NO, SH, CR, and CL lose their normal meaning and are cleared. This bit is valid only if the L bit is set.
15
1
TR
Truncate Error: Set if the receive frame is truncated (≥ 2 Kilobytes)
PRN: IP403_FEC::ReceiverError 844
The error code in the above example is 844. You can decode the message produced using information given in table.
  • Byte A is 0 and so was not shown.
  • Byte B is 8, which is 1000 in binary, so bit 4 (L) is set.
  • Byte C is 4, which is 0100 in binary, so bit 9 (N/U) is set.
  • Byte D is 4, which is 0100 in binary, so bit 13 (CR) is set.
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