Dynamic components (component switcher)

The ComponentSwitcher is a module within the blockserver which is responsible for dynamically editing configurations in response to a PV value update. It adds and removes components to all configurations to achieve this.

Configuration

The config switcher configuration file is in

C:\Instrument\Settings\config\...\configurations\ComponentSwitcher\component_switcher.json

and has a structure similar to the following:

[
    {
        "pv": "PARS:USER:R0",
        "is_local": true,
        "value_to_component_map": {
            "0.0": "test1",
            "1.0": "test2"
        }
    }
]

Where:

• pv is the PV which should be monitored for changes
• is_local controls whether the local PV prefix should be prepended to the PV before the monitor is created
• value_to_component_map is a dict mapping the pv values as strings to dynamic components which should be added
  • These values must be strings as they are JSON dict keys. The monitor will cast all received values using str()

Overview

When a monitor is received, the following actions take place:

• The value is cast to a string
• If the value has a non-zero STAT or SEVR, the update is logged but then ignored (we don't want to change configs based on an invalid value from hardware)
• If the value is not present as a key in value_to_component_map, the update is ignored and an error is logged
• For each configuration:
  • Remove all components which are present in both the configuration and the value_to_component_map, except the component which corresponds to the value just received
  • Add the component which corresponds to the value in value_to_component_map, if it was not already present
  • If the configuration changed, save it to disk
  • If this is the current configuration and it changed, reload the config to get the changes

Dynamic components

The ConfigSwitcher will only add and remove components which are marked with the isDynamic flag. To mark a config as "dynamic", go into the edit component menu and tick the "dynamic" option. Note that this option applies to the components being added/removed, not the configuration they are added to (otherwise every configuration on MuSR would need to be marked as dynamic).

Debugging

The ComponentSwitcher logs to the blockserver log with the prefix ComponentSwitcher: .