Board Features
9
2.6
Redundant MMC Flash & FWUM
The MMC microcontroller runs a firmware from its internal 256KB flash. It is programmed by another
microcontroller named FWUM (FirmWare Update Manager). The FWUM keeps the last two copies of
the MMC firmware in dedicated flash memories. The FWUM act as a watchdog to the MMC and can
rollback a firmware update in the MMC in case of problems.
The FWUM itself is a microcontroller with internal flash to store MMC firmware image. This
microcontroller is also an external watchdog for the MMC. Functions of this microntroller are kept to
a minimum. The FWUM firmware is field updatable.
2.7
Hardware Management Overview
The RTM communicates with the Module Management Controller (MMC) using the IPMB_L channel.
The memory subsystem of the MMC consists of an integrated flash memory to hold the MMC
operation code and integrated RAM for data. The field replacement unit (FRU) inventory
information is stored in the nonvolatile memory on an EEPROM connected via a local I2C interface
to the MMC microcontroller. It is possible to store up to 4 KBytes within the FRU inventory
information. Event generation over IPMB-L bus to reach the RTM that forward it to the ShMc ensure
that 'post-mortem' logging information is available even if the power of the RTM is disabled.
The onboard DC voltages and temperature are monitored by the MMC microcontroller device. The
MMC will send an event to the RTM if any of the thresholds are exceeded.
To increase the reliability of the RTM8020 SBC management subsystem, an external watchdog
supervisor only for the MMC is implemented. The MMC must strobe the external watchdog at two-
second intervals to ensure continuity of operation of the board's management subsystem. If the
MMC ceases to strobe the watchdog supervisor, the watchdog isolates the MMC from the IPMBs and
resets the MMC. The watchdog supervisor does not reset the payload power and the restart of the
MMC will not affect the payload and will restore the previous Module Hot Swap state. The watchdog
timeout expires after six seconds if strobes are not generated. 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 MMC is implemented in a second microcontroller. This microcontroller
is responsible to monitor the MMC and to manage MMC fail safe firmware upgrade process. The name
of this second microcontroller is the Firmware Upgrade Manager (FWUM). The FWUM can handle two
Note:
The MMC and the FWUM have an internal hardware watchdog.