Overview

The phosphor-power-sequencer application powers the chassis on/off and monitors the power sequencer device.

If the chassis power good (pgood) status changes to false unexpectedly, the application uses information from the power sequencer device to determine the cause. Typically this is a voltage rail that shut down due to a fault.

Application

The application is a single-threaded C++ executable. It is a 'daemon' process that runs continually. The application is launched by systemd when the BMC reaches the Ready state and before the chassis is powered on.

The application is driven by an optional, system-specific JSON configuration file. The config file is found and parsed at runtime. The parsing process creates a collection of C++ objects. These objects represent the power sequencer device, voltage rails, GPIOs, and fault checks to perform.

Power sequencer device

A power sequencer device enables (turns on) the voltage rails in the correct order and monitors them for pgood faults.

This application currently supports the following power sequencer device types:

• UCD90160
• UCD90320

Additional device types can be supported by creating a new sub-class within the PowerSequencerDevice class hierarchy.

Powering on the chassis

• A BMC application or script sets the state property to 1 on the org.openbmc.control.Power D-Bus interface.
• The phosphor-power-sequencer application writes the value 1 to the named GPIO power-chassis-control.
  • This GPIO is defined in the device tree. The GPIO name is defined in the Device Tree GPIO Naming in OpenBMC document
• The power sequencer device powers on all the voltage rails in the correct order.
• When all rails have been successfully powered on, the power sequencer device sets the named power-chassis-good GPIO to the value 1.
  • This GPIO is defined in the device tree. The GPIO name is defined in the Device Tree GPIO Naming in OpenBMC document
• The phosphor-power-sequencer application sets the pgood property to 1 on the org.openbmc.control.Power D-Bus interface.
• The rest of the boot continues

Powering off the chassis

• A BMC application or script sets the state property to 0 on the org.openbmc.control.Power D-Bus interface.
• The phosphor-power-sequencer application writes the value 0 to the named GPIO power-chassis-control.
• The power sequencer device powers off all the voltage rails in the correct order.
• When all rails have been successfully powered off, the power sequencer device sets the named power-chassis-good GPIO to the value 0.
• The phosphor-power-sequencer application sets the pgood property to 0 on the org.openbmc.control.Power D-Bus interface.

Pgood fault

A power good (pgood) fault occurs in two scenarios:

• When attempting to power on the chassis:
  • The power sequencer device is powering on all voltage rails in order, and one of the rails does not turn on.
• After the chassis was successfully powered on:
  • A voltage rail suddenly turns off or stops providing the expected level of voltage. This could occur if the voltage regulator stops working or if it shuts itself off due to exceeding a temperature/voltage/current limit.

If the pgood fault occurs when attempting to power on the chassis, the chassis pgood signal never changes to true.

If the pgood fault occurs after the chassis was successfully powered on, the chassis pgood signal changes from true to false. This application monitors the chassis power good status by reading the named GPIO power-chassis-good.

Identifying the cause of a pgood fault

It is very helpful to identify which voltage rail caused the pgood fault. That determines what hardware potentially needs to be replaced.

Determining the correct rail requires the following:

• The power sequencer device type is supported by this application
• A JSON config file is defined for the current system

If those requirements are met, the application will attempt to determine which voltage rail caused the chassis pgood fault. If found, an error is logged against that specific rail.

If those requirements are not met, a general pgood fault error is logged.

JSON configuration file

This application is configured by an optional JSON configuration file. The configuration file defines the voltage rails in the system and how they should be monitored.

JSON configuration files are system-specific and are stored in the config_files sub-directory.

Documentation is available on the configuration file format.

If no configuration file is found for the current system, this application can still power the chassis on/off and detect chassis pgood faults. However, it will not be able to determine which voltage rail caused a pgood fault.

Key Classes

• PowerInterface
  • Defines the org.openbmc.control.Power D-Bus interface.
  • The state property is set to power the chassis on or off. This contains the desired power state.
  • The pgood property contains the actual power state of the chassis.
• PowerControl
  • Created in main(). Handles the event loop.
  • Sub-class of PowerInterface that provides a concrete implementation of the org.openbmc.control.Power D-Bus interface.
  • Finds and loads the JSON configuration file.
  • Finds power sequencer device information.
  • Creates a sub-class of PowerSequencerDevice that matches power sequencer device information.
  • Powers the chassis on and off using the power-chassis-control named GPIO.
  • Monitors the chassis pgood status every 3 seconds using the power-chassis-good named GPIO.
  • Enforces a minimum power off time of 15 seconds from cold start and 25 seconds from power off.
• DeviceFinder
  • Finds power sequencer device information on D-Bus published by EntityManager.
• Rail
  • A voltage rail that is enabled or monitored by the power sequencer device.
• PowerSequencerDevice
  • Abstract base class for a power sequencer device.
  • Defines virtual methods that must be implemented by all child classes.
• StandardDevice
  • Sub-class of PowerSequencerDevice that implements the standard pgood fault detection algorithm.
• PMBusDriverDevice
  • Sub-class of StandardDevice for power sequencer devices that are bound to a PMBus device driver.
• UCD90xDevice
  • Sub-class of PMBusDriverDevice for the UCD90X family of power sequencer devices.
• UCD90160Device
  • Sub-class of UCD90xDevice representing a UCD90160 power sequencer device.
• UCD90320Device
  • Sub-class of UCD90xDevice representing a UCD90320 power sequencer device.
• Services
  • Abstract base class that provides an interface to system services like error logging and the journal.
• BMCServices
  • Sub-class of Services with real implementation of methods.
• MockServices
  • Sub-class of Services with mock implementation of methods for automated testing.

Testing

Automated test cases exist for most of the code in this application. See testing.md for more information.