ANSI/VITA 46.11 lets a VPX plug-in module implement system management at one of three tiers. Each tier is a superset of the one below it. The tier sets which IPMI commands the module's IPMC must answer and what the Chassis Manager can expect from it.
Tier-1: the mandatory minimum
A Tier-1 IPMC answers the Chassis Manager's questions. It reports its device ID and FRU address, runs a self test, describes its sensors in a Device SDR repository, returns sensor readings, lets the Chassis Manager read and write its FRU inventory, and supports Set IPMB State so the Chassis Manager can take a failed bus out of use. It does not send messages of its own.
Tier-1 is enough when the Chassis Manager only needs to discover modules, read their inventory and poll their sensors.
Tier-2: events and resets
Tier-2 adds the IPMC's own voice. It sends Platform Event messages to the Chassis Manager when a sensor crosses a threshold, so faults are reported when they happen instead of at the next poll. It also adds Cold Reset and FRU Control Capabilities.
Choose Tier-2 when the system has to react to faults promptly, or when the Chassis Manager requires events.
Tier-3: full management
Tier-3 adds the rest: Warm Reset and FRU Control, FRU activation and policy, payload modes, per-sensor event enables, a System Event Log with its own time, the FRU hash, Mandatory Sensor Numbers, BMC global enables, and IPMB at 400 kHz.
Choose Tier-3 when the Chassis Manager controls payload activation itself, when the system keeps a log of events on each module, or when the system specification calls for it.
Side by side
| Tier | Commands in our IPMC | What the tier adds |
|---|---|---|
| Tier-1 | 14 | Device ID, self test, Device SDR, sensor readings, FRU inventory read and write, Set IPMB State, FRU address information |
| Tier-2 | 18 | Platform Event messages, event receiver, Cold Reset, FRU Control Capabilities |
| Tier-3 | 36 | Warm Reset, FRU Control, activation and policy, payload modes, sensor event enables, System Event Log, FRU hash, 400 kHz IPMB |
The command counts are those of the IronKernel IPMC. Other implementations count optional commands differently.
How to pick a tier
- Start from the Chassis Manager. Its documentation, or the system specification, says which tier it expects from plug-in modules.
- Plan for the next program. A module designed for Tier-1 today may go into a Tier-3 chassis later. Firmware that builds every tier from one source tree turns that into a build switch.
- Check the hardware. Tier-3 adds 400 kHz IPMB, so check that your I2C ports and bus layout support it.
The IronKernel IPMC builds Tier-1, Tier-2 and Tier-3 from one Rust source tree.