Kontron AT8902M - Manual (Page 75)

AT8902M Software Description
Page 4 - 10 AT8902M User Guide
4.4 IPMI Firmware
The PPC communicates with the Intelligent Platform Management Controller (IPMC) using the
Keyboard Controller Style (KCS) interface. The bootloader is able to communicate with the IP-
MC, e.g. for POST error logging purposes and fault resilient purposes.
The memory subsystem of the IPMC consists of an integrated flash memory to hold the IPMC
operation code and integrated RAM for data. The field replaceable unit (FRU) inventory infor-
mation is stored in the nonvolatile memory on an EEPROM connected via a local I2C interface
to the IPMC microcontroller. It is possible to store up to 4 Kbytes within the FRU inventory in-
formation. Communication over IPMB bus to the ShMC ensures that ‘post-mortem’ logging in-
formation is available even if the main processor becomes disabled.
The IPMC provides six I2C bus connections. Two are used as the redundant IPMB bus con-
nections to the backplane, one is used for IPMB-L bus with AMC modules, one for the connec-
tion to a managed RTM, one for the Base Board and Mezzanine Sensors and one is for local
EEPROM storage.
If an IPMB bus fault or IPMC failure occurs, IPMB isolators are used to switch and isolate the
backplane/system IPMB bus from the faulted Hub Board. If possible, the IPMC activates the
redundant IPMB bus to re-establish system management communication to report the fault.
The onboard DC voltage, current, and temperature sensors are monitored by the IPMC micro-
controller continuously. The IPMC will log an event into the ShMC’s System Event Log (SEL) if
any of the thresholds are exceeded.
To increase the reliability of the Hub board management subsystem, an external watchdog su-
pervisor for the IPMC is implemented. The IPMC strobes the external watchdog at two-second
intervals to ensure continuity of operation of the board’s management subsystem. If the IPMC
ceases to strobe the watchdog supervisor for more than six seconds, the watchdog isolates the
IPMC from the IPMBs and resets the IPMC. The watchdog supervisor does not reset the pay-
load power and the restart of the IPMC will not affect the payload and will restore the previous
Hot Swap state and power level negociated with the ShMC. The external watchdog supervisor
is not configurable and must not be confused with the IPMI v1.5 watchdog timer commands.
This external watchdog of the IPMC is implemented in a second microcontroller. This Firmware
Upgrade Manager (FUM) is responsible for monitoring the IPMC and for managing the IPMC
fail safe firmware upgrade process. The FUM keeps two IPMC Firmware code images in two
external SEEPROM memories. If a failure occurs during firmware upgrade, the FUM will auto-
matically rollback to the last known working IPMC firmware image.