IPMI Watchdog Timers¶
The IPMI watchdog timers that are typically used are the FRB2 and OS timers. The FRB2 timer is used for UEFI boot and is typically configured during PEI and torn down at ready to boot in the BDS phase. The OS watchdog timer will be configured at exit boot services and will be handed off to the OS to maintain.
The IPMI feature package provides two methods for configuring and controlling the watchdog timers. The watchdog lib and the Watchdog modules. The library provides the ability to generically configure, stop, and start a given watchdog timer while the module will do this automatically based on fixed or dynamic PCDs. Platforms that need strong control over the watchdog configuration, either for a particular timer or all may use the library directly. The library and module may be used in tandem, but it may not be desirable to use both the library and module in the same phase to avoid unexpected behavior or timing issues.
The PEI implementation of the watchdog timer will configure the FRB2 timer, if enabled, at its entry during PEI. The DXE implementation will check the timer state on entry and set up a callback for ReadyToBoot to disable the FRB2 timer and ExitBootServices to enable the OS watchdog timer. Because the OS watchdog timer is based on dynamic PCDs, this configuration can be dynamically updated at boot time by any platform component so long as it's done before ExitBootServices.