PVI IOC Introspection

PVI can be used to add info tags to existing EPICS database to create a V4 PV with an NTTable of the PVs within the IOC. This can be done with the format_template function by passing a Device instance, a PV prefix and an output path to write the template to. Or, using the CLI command pvi generate-template with a pvi.device.yaml. The PV prefix is the prefix of the PVI PV itself. Usually this would match the prefix of the actual PVs, as defined in the Device signals, but it doesn’t have to.

Template Format

This will generate a new template containing records for all of the signals in the Device that inserts an info tag to the existing record.

record("*", "$(P)$(R)Gain") {
    info(Q:group, {
        "$(P)$(R)PVI": {
            "pvi.Gain.w": {
                "+channel": "NAME",
                "+type": "plain",
            }
        }
    })
}

record("*", "$(P)$(R)Gain_RBV") {
    info(Q:group, {
        "$(P)$(R)PVI": {
            "pvi.Gain.r": {
                "+channel": "NAME",
                "+type": "plain",
            }
        }
    })
}
...
record("*", "$(P)$(R)UniqueId_RBV") {
    info(Q:group, {
        "$(P)$(R)PVI": {
            "pvi.UniqueId.r": {
                "+channel": "NAME",
                "+type": "plain",
            }
        }
    })
}
...
record("*", "$(P)$(R)WaitForPlugins") {
    info(Q:group, {
        "$(P)$(R)PVI": {
            "pvi.WaitForPlugins.w": {
                "+channel": "NAME",
                "+type": "plain",
            }
        }
    })
}

These info tags are then collected and served as a V4 PV by QSRV. This info tag adds an entry into the V4 PV $(P)$(R)PVI with the name pvi.GainX.w where w is the access mode (r, w, rw, x). Each Device in the IOC will produce its own PVI PV, differentiated by the R macro in this case.

For more information on the syntax of the info tags, see the QSRV documentation.

PVI NTTable

With an IOC running the PVI PV can be accessed using PVAccess, for example the pvget CLI tool in PVAccessCPP, or the p4p python library.

❯ pvget SIM:DET:PVI
SIM:DET:PVI structure
    structure record
        structure _options
            boolean atomic true
    structure pvi
        structure Gain
            string r SIM:DET:Gain_RBV
            string w SIM:DET:Gain
...
        structure UniqueId
            string r SIM:DET:UniqueId_RBV
...
        structure WaitForPlugins
            string w SIM:DET:WaitForPlugins