Description

This article explains about "MPCS-0 PCI Error" & "pmbus read failed for cmd 0x8b" syslog message that is reported on Junos devices.

Symptoms

 

  • The "pmbus read failed for cmd 0x8b" syslog error indicates that the router's processor attempted to read the PMBus voltage value from the MAX20731 regulator using command 0x8B over the internal I2C bus, but the request timed out, resulting in an MPCS-0 PCI Error. 
  • This error is flagged when the system loses communication with a specific component on line card slot 0 (MPC0) over the internal Peripheral Component Interconnect (PCI) data bus.
  • Consequently, the FPC may terminate or reset, generating the CHASSISD_IPC_CONNECTION_DROPPED message. This message reports the occurrence of the event and is not itself an error.

 


Jul 31 06:32:26 %PFE-3: fpc3 MPCS-0 PCI Error detected. 
Jul 31 06:32:26 %PFE-3: fpc3 mpcs_pio_read_u32: MPCS(0) failed: pio_handle 0xe05b5cc0 addr 0x00000828 
Jul 31 06:32:26 %PFE-3: fpc3 mpcs_i2c_smem_start: MPCS(0) ctlr 1 prio 0 is busy 
Jul 31 06:32:26 %PFE-3: fpc3 I2C Failed device: MAX20731/VT7408:U13701:POL 1.0V A, group 0x37 address 0x55 
Jul 31 06:32:26 %PFE-3: fpc3 pmbus_npcfpc_smb_read: npc_smb_read failed for group 0x37 addr 0x55 cmd 0x8b bytes 2 
Jul 31 06:32:26 %PFE-3: fpc3 pmbus_read_volt: stout-6xqsfpp-pic - MPC7E-PIC-PMBUS-1V0-MAX20731_A: pmbus read failed for cmd 0x8b 
Jul 31 06:32:26 %PFE-3: fpc3 MPCS-0 PCI Error detected. 
Jul 31 06:32:26 %PFE-3: fpc3 mpcs_pio_read_u32: MPCS(0) failed: pio_handle 0xe05b5cc0 addr 0x00000828 
Jul 31 06:32:26 %PFE-3: fpc3 mpcs_i2c_single_io: MPCS(0) ctlr 1 prio 0 is busy 
Jul 31 06:32:26 %PFE-3: fpc3 I2C Failed device: PCA9548:U40017:I2C MUX Pwr Mux, group 0x48 address 0x77 
Jul 31 06:32:26 %PFE-3: fpc3 Failed to enable PCA9548(0x77):grp(0x48)->channel(7) 
Jul 31 06:32:26 %PFE-3: fpc3 cmtfpc_i2c_setup_mux setup_pca9548_mux failed for group 0x37 chan 7 
Jul 31 06:32:32 %DAEMON-6-PPMD_PFE_SHUTDWN: PPMD: Connection Shutdown/Closed with PFE: fpc3 
Jul 31 06:32:34 %DAEMON-3-CHASSISD_IPC_CONNECTION_DROPPED: Dropped IPC connection for FPC 3

 

The following messages are logged in syslog when the I2C primary fails to read the output voltage (0x8b) value of the I2C backup device LTC3887 voltage regulator on address 0x48 within the given timeout period due to a transient pmbus slow bus transactions.

This can vary with the card type or device type in multiple platforms.

May 29 14:36:15 %PFE-3: fpc1 mpcs_i2c_single_io: MPCS(0) ctlr 3 group 0 addr 0x48 prio 0 flags 0x10 failed status 0x1
May 29 14:36:15 %PFE-3: fpc1 I2C Failed device: group 0xabcd address 0x48
May 29 14:36:15 %PFE-3: fpc1 pmbus_npcfpc_smb_write: npc_smb_write failed for group 0xabcd addr 0x48 cmd 0x0 bytes 1
May 29 14:36:15 %PFE-3: fpc1 ltc3880_pmbus_access_setup: Could not enable channel (channel 0)
May 29 14:36:15 %PFE-3: fpc1 pmbus_read_volt: summit-srx1ru-mpc - LTC3887-VDD3V3-PW-OUT: pmbus read failed for cmd 0x8b


 
Solution
 


  • Occasionally, the occurrence of syslog messages once or twice can be safely ignored because they do not cause any functional impact.
  • Multiple occurrence of an error messages are typically a symptom of a component having issues and being restarted in an attempt to recover.
  • If the issue is seen repeatedly even after FPC reboot, contact Support for further investigation and assistance.


 
Modification History
05-07-2023: Initial version