SoftIOC services¶

This guide covers how to install EPICS SoftIOCs as a systemd service on a NixOS machine.

SoftIOCs don’t depend on any EPICS support module, and are generally described by their database content only.

Tip

Contrary to IOC services, this module is for deploying “soft” IOCs that don’t depend on any EPICS support module.

Create a service¶

To create a service, set any option inside services.softIocs.<name>. For example, to run an empty SoftIOC without any PV, set:

softioc.nix — Creating a SoftIOC named mySoftIoc¶

{
  services.softIocs.mySoftIOC.dbText = "";
}

Set a description¶

To set a description for your IOC, use the description option. This description is used in the systemd service and will be shown in systemd logs.

softioc.nix — Setting a description¶

{
  services.softIocs.mySoftIOC = {
    description = "My super documented IOC";
    # ...
  };
}

Specify the database¶

Inline¶

To specify the content of the EPICS database as a string in the NixOS configuration, use the dbText option:

softioc.nix — Creating a SoftIOC named mySoftIoc¶

{
  services.softIocs.mySoftIOC.dbText = ''
    record(ai, MY_PV) {
      # ...
    }

    # ...
  '';
}

As a separate file¶

To specify the content of the EPICS database as a separate file, use the dbFiles option:

softioc.nix — Creating a SoftIOC named mySoftIoc¶

{
  services.softIocs.mySoftIOC.dbFiles = [ ./mySoftIOC.db ];
}

Enable pvAccess¶

To make your SoftIOC expose PVs in both Channel Access and pvAccess, through PVXS’ QSRV2 mechanism, use the services.softIocs.<name>.pvAccess.enable option:

softioc.nix — Creating a pvAccess SoftIOC¶

{
  services.softIocs.mySoftIOC = {
    dbFiles = [ ./mySoftIOC.db ];
    pvAccess.enable = true;
  };
}

Specify macros¶

To specify macros, use the macros option:

softioc.nix — Creating a pvAccess SoftIOC¶

{
  services.softIocs.mySoftIOC = {
    dbFiles = [ ./mySoftIOC.db ];
    macros = {
      P = "MY:PREFIX:";
      CALC = "2 + 2";
    };
  };
}

Specify bound port and other protocol parameters¶

To specify on which port the SoftIOC must listen, and other Channel Access and pvAccess parameters, use the environment option:

softioc.nix — Set Channel Access parameters¶

{
  services.softIocs.mySoftIOC = {
    dbFiles = [ ./mySoftIOC.db ];
    environment = {
      # Listen on port 5066
      EPICS_CAS_SERVER_PORT = "5066";
      # Only listen on this IP address
      EPICS_CAS_INTF_ADDR_LIST = "192.168.1.3";
    };
  };
}

Note

The configuration set in environment.epics also influences the SoftIOC environment, and sets variables like EPICS_CA_ADDR_LIST, EPICS_CA_AUTO_ADDR_LIST, and related.