pseq: Add README for source file directory
Add a README markup file describing the classes contained in the source
file directory.
Signed-off-by: Jim Wright <jlwright@us.ibm.com>
Change-Id: Ibd150ac648f3216631f3a547f7b80b73b30f5041
diff --git a/phosphor-power-sequencer/src/README.md b/phosphor-power-sequencer/src/README.md
new file mode 100644
index 0000000..21e6f3f
--- /dev/null
+++ b/phosphor-power-sequencer/src/README.md
@@ -0,0 +1,47 @@
+## Overview
+
+This directory contains the source code for applications performing system power
+on and off control, and power sequencer device configuration and monitoring.
+
+## Class Descriptions
+
+### PowerControl
+
+Implements GPIO control of power on / off and monitoring of the chassis power
+good. The GPIOs are defined in the device tree and are named
+`power-chassis-control` and `power-chassis-good` respectively. The chassis pgood
+is monitored on a three second poll. Enforces a minimum power off time of 15
+seconds from cold start and 25 seconds from power off.
+
+Provides the server implementation of the `org.openbmc.control.Power` D-Bus
+interface.
+
+Determines the type and I2C information of the power sequencer device with the
+Entity Manager `xyz.openbmc_project.Configuration.UCD90320` interface. If a
+specific device interface is not provided or not desired, a generic base class
+implementation (see the `PowerSequencerMonitor` class below) will be used.
+
+### PowerInterface
+
+Defines the `org.openbmc.control.Power` D-Bus interface.
+
+The `state` property is set to initiate a power on or power off sequence. The
+power good `pgood` property reflects the power state of the chassis. At power on
+time the `pgood` will lag the 'state` as the power sequencer performs its
+processing. The same lag will occur on a requested power off. Loss of `pgood`
+without a `state` change request indicates a pgood failure.
+
+### PowerSequencerMonitor
+
+Implements a generic power sequencer device monitoring interface. Used when the
+specific device type is not specified or cannot be determined. Also used as a
+base class for specific device classes. The generic implementation does not do
+any device specific analysis and does not need Entity Manager or JSON file
+configuration.
+
+### UCD90320Monitor
+
+Implements a specific UCD90320 power sequencer device monitoring class. Uses the
+Entity Manager `IBMCompatibleSystem` interface to locate its JSON based
+configuration. The loaded configuration allows pgood failure analysis to
+determine the specific voltage rail or pgood pin which has failed.