drvModbusAsynConfigure exception 3 when ASLO and PREC fields of PV are changed

["Marco A. Barra Montevechi Filho via Tech-talk" <tech-talk at aps.anl.gov>]

Hello all and good evening.

We are working with a modbus IOC, the one i asked about compiling errors here previously and Mark answered about removing modbus.dbd and leaving only modbusSupport.dbd to make it work.
The IOC has several modbus functions defined in its st.cmd file like:
drvModbusAsynConfigure("Eurotherm_EMODBUS_1_1_Wr_P", "EMODBUS", ${MBUS_SL_ADDR}, ${MBUS_WRITE}, 6, 3, 0, ${MBUS_POLL}, "");

where MBUS_SL_ADDR=1, MBUS_WRITE=6 and MODBUS_POLL=1000.
EMODBUS was defined in drvAsynIPPortConfigure("EMODBUS",{EUROTHERM_IP},0,0,1)

The above modbus function is used by a PV:

record(ao, "${BL}:EU2408:P:SOMETHING") {

  field(DESC, "P Param")

  field(DTYP, "asynInt32")

  field(OUT, "@asyn(Eurotherm_EMODBUS_1_1_Wr_P,0,1000)MODBUS_DATA")

}

 and it works fine if the PV name doesnt end stop in ":P". If the PV name is only "${BL}:EU2408:P", then we get modbus exception 3 when initializing the IOC and the PV doesnt work.
I suppose this happens because some other PV has a link to it and the link breaks when the name is changed. I dont know if there could be any cause to this behaviour.

The only PVs we found refering to "${BL}:EU2408:P:SOMETHING" PV are:

record(dfanout, "${BL}:EU2408:SETASLO") {

        field(OMSL, "closed_loop")

        field(DOL, "${BL}:EU2408:CALCASLO PP")

        field(OUTA, "${BL}:EU2408:SP.ASLO")

        field(OUTB, "${BL}:EU2408:SP:RBV.ASLO")

        field(OUTC, "${BL}:EU2408:RR.ASLO")

        field(OUTD, "${BL}:EU2408:RR:RBV.ASLO")

        field(OUTE, "${BL}:EU2408:PV:RBV.ASLO")

        field(OUTF, "${BL}:EU2408:P.ASLO")   #HERE

        field(OUTG, "${BL}:EU2408:P:RBV.ASLO")

        field(FLNK, "${BL}:EU2408:SETPREC")

}
and
record(dfanout, "${BL}:EU2408:SETPREC") {

        field(OMSL, "closed_loop")

        field(DOL, "${BL}:EU2408:PREC.RVAL")

        field(OUTA, "${BL}:EU2408:SP.PREC PP")

        field(OUTB, "${BL}:EU2408:SP:RBV.PREC PP")

        field(OUTC, "${BL}:EU2408:RR.PREC PP")

        field(OUTD, "${BL}:EU2408:RR:RBV.PREC PP")

        field(OUTE, "${BL}:EU2408:PV:RBV.PREC PP")

        field(OUTF, "${BL}:EU2408:P.PREC PP")    ######HERE

        field(OUTG, "${BL}:EU2408:P:RBV.PREC PP")

}
so i suppose altering PVs PREC and ASLO alters the correct modbus function needed to access the parameter, but this makes no sense to me since the parameter stored in the equipment should still be the same.
Does someone know what am i missing?

Thanks in advance 🙂

Marco

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