Data Sources

PyDM is shipped with a couple of data plugins:

  • EPICS

  • Archiver

EPICS

This plugin is used to allow PyDM Widgets to access to Channel Access process variables and interact with them.

Protocol

Address Format

Example

ca

ca://<PV NAME>

ca://MTEST:Float

For this particular data plugin, three options are available for the Python interface to Channel Access.

Warning

By default, PyEpics is selected unless configured through the PYDM_EPICS_LIB environment variable.

Possible values are PYEPICS, PYCA, and CAPROTO.

Archiver

This plugin is used to allow PyDM Widgets to read data from Archiver Appliance.

While still crude, this data plugin works and has been tested against a real instance of the Archiver.

Basically a HTTP request is sent to the archiver appliance and the address is used to form the parameters for the data retrieval. Warning: The request is sent synchronously, meaning it will block your application until the request is complete. This limitation will be removed in a future version.

Protocol

Address Format

Example

archiver

archiver://<PARAMS>

archiver://pv=test:pv:123&donotchunk

Warning

Different facilities must set the PYDM_ARCHIVER_URL environment variable to point to their Archiver Appliance location or the retrieval application. If not set, this variable will point to SLAC’s Archiver Appliance URL, which is almost certainly not what you want.

If your Archiver Retrieval is hosted under the following address http://lcls-archapp.slac.stanford.edu/retrieval/... set the variable to http://lcls-archapp.slac.stanford.edu.

The remaining parts of the URL will be dealt with at the Data Plugin level and should not be a concern.