Common Database patterns

Pull Alarm Status w/o Data

This is useful to bring alarm status in without affecting the value stored in a record. In the following example the alarm status of $(P):set is fetched by $(P):rbv when it is processed, but the value is read from a different record.

record(bo, "$(P):set") {
    field(OSEV, "MAJOR")
    field(FLNK, "$(P):rbv")
}

record(bi, "$(P):rbv") {
    field(SDIS, "$(P):set NPP MS")
    field(DISV, "-1")
    field(INP , "$(P):some:other:record")
}

Combined Setting and Readback

Use when a single PV is desired. Could be used to show the results of rounding in a float to fixed precision conversion.

In the following example the value read from a ‘bi’ is inverted so that the associated ‘bo’ acts as a toggle.

record(bi, "$(P):rbv") {
    field(DTYP, "...")
    field(INP , "...")
    field(SCAN, "...")
    field(PINI, "YES")
    field(FLNK, "$(P):inv")
}

record(calcout, "$(P):inv")
    field(CALC, "!A")
    field(INPA, "$(P):rbv")
    field(OUT , "$(P) NPP")
}

record(bo, "$(P)") {
    field(DTYP, "...")
    field(OUT , "...")
    field(FLNK, "$(P):rbv")
}

The important point is the NPP modifier on output link of the ‘calcout’ record. This updates the VAL field of the ‘bo’ record (and posts monitors) without processing it.

Readback from a different hardware address

Use when the readback value of an ‘out‘ record comes from a different hardware address. In this case it can be undesirable for an update of the readback value to trigger processing of the ‘out‘ record again as this could lead to infinite loops. SDIS is used to ensure that writes to the hardware only happen when they are not triggered by the readback value changing. The main record is a soft record, this ensures that monitors are updated when its value changes.

In the following example a longout record gets its readback value from a different longin record.

record(longout, "$(P)") {
    field(OUT,  "$(P):write PP")
}

record(longout, "$(P):write") {
    field(DTYP, "...")
    field(OUT,  "...")
    field(SDIS, "$(P):update.PACT")
}

record(longin, "$(P):rbv") {
    field(DTYP, "...")
    field(INP,  "...")
    field(SCAN, "...")
    field(PINI, "YES")
    field(FLNK, "$(P):update")
}

record(longout, "$(P):update") {
    field(OMSL, "closed_loop")
    field(DOL,  "$(P):rbv")
    field(OUT,  "$(P) PP")
}