README: add config via D-Bus
We can now add a virtual sensor in two ways (reading in a JSON file or a
configuration from D-Bus), so add this information into the README.
Signed-off-by: Rashmica Gupta <rashmica.g@gmail.com>
Change-Id: I63099953a5fdd3c860a728036544955f906a31f7
diff --git a/README.md b/README.md
index 32eda06..b714da9 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,41 @@
# phosphor-virtual-sensor
+
+phosphor-virtual-sensor reads in virtual_sensor_config.json
+There are two types of data in this file:
+
+#### 1) virtual sensor configuration information
+See virtual_sensor_config.json in this repository for an example. Sensors added
+this way can use any expression that is accepted by exprtk.
+
+#### 2) information to get a virtual sensor configuraton from D-Bus
+For example:
+```
+ {
+ "Desc":
+ {
+ "Config" : "D-Bus",
+ "Type" : "modifiedMedian"
+ }
+ }
+```
+Sensors added this way can only use a set of restricted calculations. At this
+stage the only type supported is modifiedMedian.
+
+The virtual sensor configuration information needs to be added into the
+relevant hardware configuration file in entity-manager. This method of adding a
+virtual sensor allows a recipe that builds for different hardware
+configurations to have different virtual sensors for each configuration.
+
+The virtual sensor configuration in entity manager follows a different format
+to the JSON in virtual_sensor_config.json (specified in
+entity-manager/schemas/VirtualSensor.json). In particular, the format for
+Thresholds is different. The following table shows the severity fields
+that correspond to a particular threshold.
+
+Threshold | Severity
+----------------|-----------
+Warning | 0
+Critical | 1
+PerformanceLoss | 2
+SoftShutdown | 3
+HardShutdown | 4