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System Overview 1-23
The system management console (SMC) is a front end PC that serves as the local console
for the system. See Section 1.8.2.
A modem for remote control connects directly to the SMC PC through the modem port.
Another modem connected to the standard I/O is used for system-initiated service calls.
The CSB uses a polled master/slave protocol where a single master controls the network.
The master, in this case the SCM, sends commands to slaves to which they respond.
Nodes on the CSB are
:
• One or up to eight SCMs (two for the GS80), one of which is the active master of the
bus (CSB master SCM) while all others are slave nodes. One other slave SCM may
be used as a redundant CSB master. It must have its environment variable
scm_csb_master_eligible set and be connected to the OCP.
• Up to 8 power system managers (PSMs), one in each QBB in the system.
• Up to 16 PCI backplane managers (PBMs), one on each PCI backplane.
• One H-switch power manager (HPM), if an H-switch is present.
With the exception of the SCM, each node is a microprocessor programmed to monitor
the subsystem it is in. The SCM’s microprocessor is programmed as the system console.
It continually polls each node to retrieve monitoring information from each slave.
By default the SCM with the lowest CSB node ID number connected to the OCP becomes
the bus master. (The node ID switch determines the node number for the SCM. Each
CSB node ID number must be unique. See Section 1.21.6.)
SCM Failover
Assuming SCM redundancy, four conditions will cause failover:
• If the default master fails self-test.
• If the default master loses connection with the OCP.
• If a new node with an eligible master SCM is added to the CSB and it has a lower
node number than the current master, then the current master relinquishes control
of the CSB and the new SCM becomes master.
• If the slave SCM node that is an eligible master does not see the master SCM
continually assert
CSB MASTER ENABLE, it becomes the master.
NOTE: Should failover occur, the SCM monitor function physically moves from
one standard I/O module to another. Note also that a powered off QBB
may power back on should failover occur or if a remote user initiates
the power-on. Putting the PSM switch in the Service position prevents
this.