This article explains why the event message
CHASSISD_I2CS_READBACK_ERROR
appears in the syslog.
The
CHASSISD_I2CS_READBACK_ERROR
is logged when the chassis process (chassisd) cannot read back information from the I2C slave (I2CS) about the indicated component (field-replaceable unit, or FRU).
Below are the symptoms for two example scenarios.
Example 1
Example 1 was due to the ribbon cable on the FPM (Front Panel Board) being improperly seated. Reseating the ribbon cable fixed the issue.
"show chassis hardware detail" Hardware inventory: Item Version Part number Serial number Description Chassis XXXXXXXXXXXX MX960 Midplane REV 03 710-013698 XXXXXX MX960 Backplane Fan Extender REV 02 710-018051 XXXXXX Extended Cable Manager FPM Board <-- FPM (Front Panel Board) data not populating. PDM Rev 03 740-013110 XXXXXXXXXXX Power Distribution Module PEM 0 Rev 06 740-013683 XXXXXXXXXXX DC Power Entry Module PEM 1 Rev 06 740-013683 XXXXXXXXXXX DC Power Entry Module PEM 2 Rev 06 740-013683 XXXXXXXXXXX DC Power Entry Module PEM 3 Rev 06 740-013683 XXXXXXXXXXX DC Power Entry Module Routing Engine 0 REV 06 740-013063 XXXXXXXXXX RE-S-2000 ad0 999 MB SILICONSYSTEMS INC 1GB 247CTy69SG705DC00181 Compact Flash ad2 38154 MB HTE541040G9SA00 MPBBTAX2KNUP2G Hard Disk Routing Engine 1 REV 06 740-013063 XXXXXXXXXX RE-S-2000 ad0 999 MB SILICONSYSTEMS INC 1GB 247CTy69SG705DC00339 Compact Flash ad2 38154 MB HTE541040G9SA00 MPBBTAX2KNX4SG Hard Disk "show log messages" Jul 17 15:00:47 chassisd[19096]: CHASSISD_I2CS_READBACK_ERROR: Readback error from I2C slave for FPM 0 ([0x8, 0x21] -> 0x0) Jul 17 15:00:49 /kernel: PCF8584(RD): target ack timeout Jul 17 15:00:49 /kernel: PCF8584(RD): (i2c_s1=0x08, group=0x8, device=0x54)
Example 2
Example 2 was caused by a bad Control Board in slot 0 that had to be replaced.
"show chassis hardware detail" Hardware inventory: Item Version Part number Serial number Description Chassis XXXXXXXXXXXX MX960 Midplane REV 03 710-013698 XXXXXX MX960 Backplane FPM Board REV 03 710-014974 XXXXXX Front Panel Display PDM Rev 03 740-013110 XXXXXXXXXXX Power Distribution Module PEM 0 Rev 04 740-013682 XXXXXXXXXXX PS 1.7kW; 200-240VAC in PEM 1 Rev 04 740-013682 XXXXXXXXXXX PS 1.7kW; 200-240VAC in PEM 2 Rev 04 740-013682 XXXXXXXXXXX PS 1.7kW; 200-240VAC in PEM 3 Rev 04 740-013682 XXXXXXXXXXX PS 1.7kW; 200-240VAC in Routing Engine 0 REV 09 740-013063 XXXXXXXXXX RE-S-2000 ad0 999 MB SILICONSYSTEMS INC 1GB B828318KD9TM0908 Compact Flash ad2 38154 MB ST940817SM 5RQ023R6 Hard Disk Routing Engine 1 REV 09 740-013063 XXXXXXXXXX RE-S-2000 ad0 999 MB SILICONSYSTEMS INC 1GB B828318KD9TM0908X102 Compact Flash ad2 38154 MB ST940817SM 5RQ026R9 Hard Disk CB 0 <-- Control Board slot 0 data not populating. CB 1 REV 03 710-021523 XXXXXX MX SCB CB 2 REV 03 710-021523 XXXXXX MX SCB FPC 0 REV 09 750-018124 XXXXXX DPCE 4x 10GE R CPU REV 07 710-013713 XXXXXX DPC PMB PIC 0 BUILTIN BUILTIN 1x 10GE(LAN/WAN) "show log messages" Jan 24 17:26:07 Xx-Xxxx-MX960_2 chassisd[4543]: CHASSISD_I2CS_READBACK_ERROR: Readback error from I2C slave for CB 0 ([0x16, 0x23] -> 0x0) Jan 24 17:26:06 Xx-Xxxx-MX960_2 init: neighbor-liveness (PID 4559) sending signal hup: due to "proto-mastership": 0x1 Jan 24 17:26:08 Xx-Xxxx-MX960_2 fpc0 RDP: Remote side reset connection: rdp.(fpc0:19473).(serverRouter:ppm) Jan 24 17:26:07 Xx-Xxxx-MX960_2 chassisd[4543]: CHASSISD_I2CS_READBACK_ERROR: Readback error from I2C slave for CB 0 ([0x16, 0x25] -> 0x0) Jan 24 17:26:08 Xx-Xxxx-MX960_2 fpc0 PPMAN disconnected; Remote side closed
The I2C master initiates all communication on the I2C bus and supplies the clock for all slave devices. If there is an issue with the I2C slave, it disrupts communication with the I2C bus and the device ID. Data is disrupted on the FRU component and does not populate the show chassis hardware detail command output. The chassisd will identify the failed FRU component in the log messages. The failed FRU component will appear in the text following the
CHASSISD_I2CS_READBACK_ERROR
message.
For example, in the following message, Control Board slot 0 is identified as the problem FRU component:
chassisd[4543]: CHASSISD_I2CS_READBACK_ERROR: Readback error from I2C slave for CB 0 ([0x16, 0x2b] -> 0x0)
The most probable cause for the
CHASSISD_I2CS_READBACK_ERROR
is a hardware error.
Perform these steps to determine the cause and resolve the problem (if any). Continue through each step until the problem is resolved.
1. Collect the show command output.
Capture the output to a file (in case you have to open a technical support case). To do this, configure each SSH client/terminal emulator to log your session.
show chassis hardware detail show log messages
2. Analyze the show command output.
- There are many different hardware components on the chassis; for detailed information about the output of many possible show commands, see the Ethernet Interfaces Feature Guide for Routing Devices.
- After you have identified the device that is the problem, try reseating the device. After the device is pulled, check for bent pins on the chassis slot and for burn marks where the pins meet the device.
Note: On MX Series routers, the FPM (Front Panel Board) is connected via a ribbon cable between the chassis and the FPM. The ribbon cable may need to be reseated at the chassis as well as the FPM board.