Experimental Physics and
Industrial Control System

Michael Davidsaver <[email protected]> · Tue, 14 Aug 2018 09:41:27 -0700

> Only the data for fields that change value between requests are sent.”

A more precise statement would be, "only data for fields marked as changed will be sent".
So this is only done if the server (or ChannelProvider generally) manages a "what changed" bit set.
Setting bit #0 is the shorthand for "everything changed".

eg. QSRV does this tracking for Monitor, but not Get.

https://github.com/mdavidsaver/pva2pva/blob/master/pdbApp/pdbsingle.cpp#L410-L411

... as I think about it, it should (now) be possible to remove these two lines.

On 08/14/2018 09:12 AM, Heinz Junkes wrote:
> I have a question about bitSets.
> 
> I use the example program from exampleCPP get.cpp
> with the code fragment
> 
>         PvaClientGetDataPtr data = pvaClientGet->getData();
>         BitSetPtr bitSet =  data->getChangedBitSet();
> 
> Cardinality is "1" although obviously nothing changes.
> Bit #0 is set “structure”.
> 
> Now to my question. Is bitSet set by the server?
> 
> And then I don't understand that either (from the documentation).
> 
> "Only fields that change are transmitted.
> Only the data for fields that change value between requests are sent.”
> 
> in the pvaGet I only request “value”.
> 
> The PV I am looking at is a classic V3 PV (ca) and on my server runs pvAccess-Server (qsrv).
> 
> ioc:
> 
> dbpr CRYAFM:AWG0:DDSA:SetDDSFreq,4
> 
> ACKS: NO_ALARM      ACKT: YES           ADEL: 0             ALST: 123456        
> AOFF: 0             ASG:                ASLO: 0             ASP: 0x0            
> BKLNK: 00 00 00 00 00 00 00 00 00 00 00 00                  BKPT: 00            
> DESC: Frequency DDS DDSA:               DISA: 0             DISP: 0             
> DISS: NO_ALARM      DISV: 1             DOL:CONSTANT        DPVT: 0x19df880     
> DRVH: 0             DRVL: 0             DSET: 0x4fb724      DTYP: asynFloat64   
> EGU: Hz             EGUF: 0             EGUL: 0             EOFF: 0             
> ESLO: 1             EVNT:               FLNK:CONSTANT 0     HHSV: NO_ALARM      
> HIGH: 0             HIHI: 0             HOPR: 0             HSV: NO_ALARM       
> HYST: 0             INIT: 0             IVOA: Continue normally                 
> IVOV: 0             LALM: 123456        LBRK: 0             LCNT: 0             
> LINR: NO CONVERSION LLSV: NO_ALARM      LOLO: 0             LOPR: 0             
> LOW: 0              LSET: 0x1942808     LSV: NO_ALARM       MDEL: 0             
> MLIS: 00 00 00 00 00 00 00 00 00 00 00 00                   MLOK: 01 94 e7 40   
> MLST: 123456        NAME: CRYAFM:AWG0:DDSA:SetDDSFreq       NSEV: NO_ALARM      
> NSTA: NO_ALARM      OIF: Full           OLDSIMM: NO         OMOD: 0             
> OMSL: supervisory   ORAW: 123456        ORBV: 0             OROC: 0             
> OUT:INST_IO @asyn(awg0, 0)DDS Frequency OVAL: 123456        PACT: 0             
> PBRK: 0x0           PHAS: 0             PINI: NO            PPN: 0x0            
> PPNR: 0x0           PREC: 3             PRIO: LOW           PROC: 0             
> PUTF: 0             PVAL: 123456        RBV: 0              RDES: 0xcdc5d0      
> ROFF: 0             RPRO: 0             RSET: 0x4fbac8      RVAL: 123456        
> SCAN: Passive       SDIS:CONSTANT       SDLY: -1            SEVR: NO_ALARM      
> SIML:CONSTANT       SIMM: NO            SIMPVT: 0x0         SIMS: NO_ALARM      
> SIOL:CONSTANT       SPVT: 0x0           SSCN: <nil>         STAT: NO_ALARM      
> TIME: 2018-08-14 08:51:37.697697041     TPRO: 0             TSE: 0              
> TSEL:CONSTANT       UDF: 0              UDFS: INVALID       VAL: 123456         
> 
> humma-kavula:examples junkes$ cainfo CRYAFM:AWG0:DDSA:SetDDSFreq
> CRYAFM:AWG0:DDSA:SetDDSFreq
>     State:            connected
>     Host:             cry-test.rz-berlin.mpg.de:5064
>     Access:           read, write
>     Native data type: DBF_DOUBLE
>     Request type:     DBR_DOUBLE
>     Element count:    1
> 
> 
> humma-kavula:examples junkes$ pvinfo CRYAFM:AWG0:DDSA:SetDDSFreq
> CHANNEL  : CRYAFM:AWG0:DDSA:SetDDSFreq
> STATE    : CONNECTED
> ADDRESS  : 141.14.128.53:5075
> epics:nt/NTScalar:1.0
>     double value
>     alarm_t alarm
>         int severity
>         int status
>         string message
>     time_t timeStamp
>         long secondsPastEpoch
>         int nanoseconds
>         int userTag
>     display_t display
>         double limitLow
>         double limitHigh
>         string description
>         string format
>         string units
>     control_t control
>         double limitLow
>         double limitHigh
>         double minStep
>     valueAlarm_t valueAlarm
>         boolean active
>         double lowAlarmLimit
>         double lowWarningLimit
>         double highWarningLimit
>         double highAlarmLimit
>         int lowAlarmSeverity
>         int lowWarningSeverity
>         int highWarningSeverity
>         int highAlarmSeverity
>         double hysteresis
> 
> 
> get, nothing is changing ???
> 
> code fragment:
> 
>    void get()
>     {
> 
>         if(!channelConnected) {
>             cout << channelName << " channel not connected\n";
>             return;
>         }
>         if(!getConnected) {
>             cout << channelName << " channelGet not connected\n";
>             return;
>         }
>         pvaClientGet->get();
>         PvaClientGetDataPtr data = pvaClientGet->getData();
>         BitSetPtr bitSet =  data->getChangedBitSet();
> cout << "bitset Cardinality : " << bitSet->cardinality() << endl;
>         if(bitSet->cardinality()>0) {
>              cout << "changed " << channelName << endl;
>              data->showChanged(cout);
>              cout << "bitSet " << *bitSet << endl;
>         }
>     }
> 
> 
> output:
> 
> channelGetConnect CRYAFM:AWG0:DDSA:SetDDSFreq status Status [type=OK]
> channelGetDone CRYAFM:AWG0:DDSA:SetDDSFreq status Status [type=OK]
> bitset Cardinality : 1
> changed CRYAFM:AWG0:DDSA:SetDDSFreq
>  = epics:nt/NTScalar:1.0 
>     double value 123456
>     alarm_t alarm
>         int severity 0
>         int status 0
>         string message NO_ALARM
>     time_t timeStamp
>         long secondsPastEpoch 1534254697
>         int nanoseconds 697697041
>         int userTag 0
>     display_t display
>         double limitLow 0
>         double limitHigh 0
>         string description Frequency DDS DDSA:
>         string format 
>         string units Hz
>     control_t control
>         double limitLow 0
>         double limitHigh 0
>         double minStep 0
>     valueAlarm_t valueAlarm
>         boolean active false
>         double lowAlarmLimit nan
>         double lowWarningLimit nan
>         double highWarningLimit nan
>         double highAlarmLimit nan
>         int lowAlarmSeverity 0
>         int lowWarningSeverity 0
>         int highWarningSeverity 0
>         int highAlarmSeverity 0
>         double hysteresis 0
> 
> bitSet {0}
> 
> 
> channelGetDone CRYAFM:AWG0:DDSA:SetDDSFreq status Status [type=OK]
> bitset Cardinality : 1
> changed CRYAFM:AWG0:DDSA:SetDDSFreq
>  = epics:nt/NTScalar:1.0 
>     double value 123456
>     alarm_t alarm
>         int severity 0
>         int status 0
>         string message NO_ALARM
>     time_t timeStamp
>         long secondsPastEpoch 1534254697
>         int nanoseconds 697697041
>         int userTag 0
>     display_t display
>         double limitLow 0
>         double limitHigh 0
>         string description Frequency DDS DDSA:
>         string format 
>         string units Hz
>     control_t control
>         double limitLow 0
>         double limitHigh 0
>         double minStep 0
>     valueAlarm_t valueAlarm
>         boolean active false
>         double lowAlarmLimit nan
>         double lowWarningLimit nan
>         double highWarningLimit nan
>         double highAlarmLimit nan
>         int lowAlarmSeverity 0
>         int lowWarningSeverity 0
>         int highWarningSeverity 0
>         int highAlarmSeverity 0
>         double hysteresis 0
> 
> bitSet {0}
> 
> 
> 
> 
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System