phosphor-power-sequencer/docs/power_loss.md

1 # Power Loss
5 Power distribution in a computer system is complex. It typically flows from a
6 wall outlet to power supplies to voltage regulators to system components. Other
7 devices may exist between the wall outlet and the power supplies, such as an
8 Uninterruptible Power Supply (UPS) or an Enclosure Power Distribution Unit
11 A **brownout** is a partial reduction in voltage to the power supplies. In some
14 processor and other system components have lost power.
16 A **blackout** is a complete loss of power to the power supplies.
24 `phosphor-power-sequencer` application will take no action.
26 If the chassis was powered on when the brownout occurred, the power sequencer
27 device will normally change the chassis power good (pgood) signal from true to
28 false. `phosphor-power-sequencer` will isolate the failure to the power supply
29 rail. `phosphor-power-sequencer` will log a power supply error. This error will
30 specify the problem was the input voltage rather than the power supply hardware.
31 See [Power Good Faults](pgood_faults.md) for more information.
37 The system loses all power. It will be completely off until utility power is
40 When power is restored, if the system was previously powered on, it may be
42 application. This depends on the Auto Power Restart settings.
46 If the blackout affects all chassis, the system loses all power. It will behave
51 - The `phosphor-chassis-power` application will do the following:
62   - `phosphor-power-sequencer` will read the pgood signal for each chassis and
64     `org.openbmc.control.Power` D-Bus interface for the chassis.
69   - `phosphor-chassis-state-manager` will determine if a power problem has
73   - If a power problem has occurred, `phosphor-chassis-state-manager` will do
76     - Power the system [off](powering_off.md) and then [on](powering_on.md)