# phosphor-power-sequencer

## Overview

The `phosphor-power-sequencer` application powers all the chassis in the system
on and off. It also monitors the power good (pgood) state in each chassis.

**Note:** Many changes have been made to this documentation to define how
multiple chassis support will work. This support is not yet implemented in this
application. The support is also dependent on changes to the existing
`phosphor-chassis-state-manager` application and the planned new
`phosphor-chassis-power` application. This disclaimer will be removed when this
support is fully implemented.

## Application

`phosphor-power-sequencer` is a single-threaded C++ executable. It is a daemon
process that runs continually. It is launched by systemd when the BMC reaches
the Ready state and before the system is powered on.

`phosphor-power-sequencer` 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
chassis, power sequencer devices, voltage rails, GPIOs, and fault checks to
perform.

See [Internal Design](internal_design.md) for more information.

## Power sequencer device

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

`phosphor-power-sequencer` 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. See [Internal Design](internal_design.md)
for more information.

If the power sequencer device type is not supported, `phosphor-power-sequencer`
can still power the system on/off and detect chassis pgood faults. However, it
will not be able to determine which voltage rail caused a pgood fault.

## Powering on the system

`phosphor-power-sequencer` uses the power sequencer device to power on all main
(non-standby) voltage rails in each chassis.

See [Powering On](powering_on.md) for more information.

## Powering off the system

`phosphor-power-sequencer` uses the power sequencer device to power off all main
(non-standby) voltage rails in each chassis.

See [Powering Off](powering_off.md) for more information.

## Monitoring chassis pgood

`phosphor-power-sequencer` periodically reads the chassis pgood state from the
power sequencer device. See
[Monitoring Chassis Power Good](monitoring_chassis_pgood.md) for more
information.

## Chassis pgood faults

If the chassis pgood state is false when it should be true, a chassis pgood
fault has occurred. `phosphor-power-sequencer` uses information from the power
sequencer device to determine the cause.

See [Power Good Faults](pgood_faults.md) for more information.

## JSON configuration file

`phosphor-power-sequencer` 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](../config_files/) sub-directory.

[Documentation](config_file/README.md) is available on the configuration file
format.

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

## Testing

Automated test cases exist for most of the code in this application. See
[Testing](testing.md) for more information.

## Related applications

### phosphor-chassis-state-manager

The `phosphor-chassis-state-manager` application exists in the
phosphor-state-manager repository. It supports user requests to power on and off
the system hardware. It publishes the [`xyz.openbmc_project.State.Chassis`][1]
D-Bus interface.

### phosphor-chassis-power

The `phosphor-chassis-power` application exists in the phosphor-power
repository. It monitors the chassis input power state using GPIOs.

### phosphor-power-supply

The `phosphor-power-supply` application exists in the phosphor-power repository.
It monitors the power supply devices within each chassis.

[1]:
  https://github.com/openbmc/phosphor-dbus-interfaces/blob/master/yaml/xyz/openbmc_project/State/Chassis.interface.yaml