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130 MPCMM0001 Chassis Management Module Software Technical Product Specification
CDMs and FRU Information
CDMs and FRU Information 15
15.1 Chassis Data Module
There are two chassis data modules (CDMs) in a chassis for redundancy.Each CDM has 2
EEPROMs containing the FRU information for the chassis. The CDM FRU data is also cached on
the CMMs at boot time.
The CDM stores serial number and asset information about chassis and provides PICMG 3.0 shelf
FRU information, such as number of slots, slot connection/routing information (for electronic
keying), and max power per feeds.
15.2 FRU/CDM Election Process
When the CMMs first boot up, there is an CDM election process to determine the valid CDM
contents. At least one valid set of CDM data must exist for the election to succeed. A CDM data set
is considered valid if the Active CMM can read it and the checksum computes
During the initial bootup process, the CMM needs to elect which CDM’s FRU information to use
to retrieve critical chassis information. The election is a simple majority process:
1. Three matching sets of CDM data win the election.(3-1).
2. Two matching sets of CDM data win if the other two are split (2-1-1) or if one is missing (2-1-
x)
3. If matched sets are split 2-2, CDM1 wins
4. If there are no matched data sets, then CDM priority is determined by first available, valid
data. The priority is determined in the following order:
—CDM1
—CDM2
— Local cache (/etc/cmm/sfrucache)
— Remote cache (/usr/sfrucache)
The highest-ranking member of the winning "team" in a 3-1, 2-1-1, or 2-1-x result is elected the
defining CDM authority
15.3 FRU Information
The CMM can query the entire FRU of a device, entire areas of a FRU, or individual fields in the
different areas of the FRU.
For detailed information on FRU requirements, please refer to the PICMG 3.0 Specification.