phosphor-power-sequencer/docs/pgood_faults.md

1 # Power Good Faults
5 The power sequencer device provides a chassis power good (pgood) signal. This
6 indicates that all of the main (non-standby) voltage rails are powered on.
8 If the chassis pgood state is false when it should be true, a chassis power good
11 ## Pgood fault while powering on the system
13 When the power sequencer device is powering on the main voltage rails in order,
14 one of the rails may fail to power on. This is often due to a hardware problem.
16 When a voltage rail fails to power on, the power sequencer device may
18 for the rail to power on. In both cases the chassis pgood signal never changes
21 ## Pgood fault after the system was powered on
23 A pgood fault can occur after a system has been powered on. The system may have
26 A voltage rail may suddenly power off or stop providing the expected level of
30 The power sequencer device will detect that the voltage rail has failed. The
32 may also power off several other related voltage rails, depending on how the
37 `phosphor-power-sequencer` detects a pgood fault by monitoring the chassis pgood
40 - Powering on chassis: pgood signal never changes to true.
41 - Chassis was powered on: pgood signal changes from true to false.
43 When a pgood fault is detected, `phosphor-power-sequencer` will perform the
46 - Use information from the power sequencer device to determine the cause of the
48 - Log an error with information about the fault.
49 - If this is a single chassis system:
50   - The system will be [powered off](powering_off.md).
51 - If this is a multiple chassis system:
52   - Wait a short period of time, and then check if all the other chassis that
53     were powered on are also experiencing a pgood fault. If so, check if any
55     is a chassis-specific problem or a system-wide problem due to a
56     [Power Loss](power_loss.md).
57   - If this is a chassis-specific problem, add the inventory path of the chassis
60   - The system will be powered [off](powering_off.md) and then
61     [on](powering_on.md) again.
62   - Chassis with an `Enabled` value of false will **not** be powered back on.
64 See [Chassis Status](chassis_status.md) for more information on the `Enabled`
67 Note that when a pgood error happens **during** a power on attempt, the
68 `phosphor-chassis-state-manager` application handles the power off/power cycle.
69 When the pgood error happens **after** the system was powered on, the
70 `phosphor-power-sequencer` application handles the power off/power cycle. This
71 is due to the complex service file relationships that occur during a power on
81 - The power sequencer device type is supported by `phosphor-power-sequencer`.
82 - A [JSON configuration file](config_file/README.md) is defined for the system.
86 If those requirements are met, `phosphor-power-sequencer` will attempt to
90 - Read a GPIO from the power sequencer device
91 - Check the PMBus STATUS_VOUT command value
92 - Compare the PMBus READ_VOUT value to the PMBus VOUT_UV_FAULT_LIMIT value
94 Multiple methods might need to be used on the same rail. For example, the PMBus
96 on, but they might not be set during a power on attempt because the power
97 sequencer is waiting indefinitely for the rail to power on.
104 If the voltage rail is from the power supplies, and the `phosphor-power-supply`
105 application found a power supply error, then the power supply error is logged as