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<== Date ==> <== Thread ==>

Subject: Re: [CA][waveform] how to NELM?
From: Matthieu Bec <[email protected]>
To: Pavel Masloff <[email protected]>
Cc: EPICS Tech Talk <[email protected]>
Date: Sat, 12 May 2012 07:57:44 -0700

Hello Pavel,
look at the mechanics in catools/caget.c for inspiration.
your last attempt segfaults because at one point or another you need to provide a buffer with sufficient (usually allocated) space to hold the result. when that happens depends on the 'callback' flag - in your synchronous case, follow callback=false.
your first attempt seemed somewhat closer because you did malloc.

Regards
Matthieu


On 05/12/12 00:27, Pavel Masloff wrote:
It's a strange thing. On Windows (VisualStudio 2010) this code works
despite the warning, on Linux I get segmentation fault.
I should have written pValue = wave.value but in this case it doesn't
work even on Windows.
Can anyone check my code? I need to read a waveform (FTVL=UCHAR) via CA
in C.

On Sat, May 12, 2012 at 1:26 AM, Pavel Masloff <[email protected]
<mailto:[email protected]>> wrote:

    Alright, here it works. If someone's interested:

    #include <stddef.h>
    #include <stdlib.h>
    #include <stdio.h>
    #include <string.h>
    #include "cadef.h"

    const char *channel_state_str[4] = {
    "not found",
    "connection lost",
    "connected",
    "closed"
    };

    typedef struct {
         chid channel;
         int status;
         long value;
    } epicsShortPV;

    typedef struct {
         chid channel;
         int status;
         long number;
         unsigned short* value;
    } epicsWavePV;




    /* Connect a PV to a channel */
    #define casearch(name, pv) SEVCHK(\
         (pv).status = (ca_search((name), &(pv).channel)), name)

    /* get full information about a PV */
    #define cainfo(pv, type) SEVCHK(\
         (pv).status = (ca_state((pv).channel) != cs_conn ? ECA_DISCONN : \
         ca_get(dbf_type_to_DBR(type), (pv).channel, &(pv).value)),
    ca_name((pv).channel))

    /* get only usually changing information about a PV */
    #define caget(pv, type) SEVCHK(\
         (pv).status = (ca_state((pv).channel) != cs_conn ? ECA_DISCONN : \
         ca_get(dbf_type_to_DBR_STS(type), (pv).channel, &(pv).data)),
    ca_name((pv).channel))


    void printPV(const epicsShortPV* pv)
    {
         if (ca_state(pv->channel) == cs_conn)
         {
             printf("%s =  %d \n", ca_name(pv->channel), pv->value);
         }
         else
         {
             printf("%s: <%s>\n",ca_name(pv->channel),
    channel_state_str[ca_state(pv->channel)]);
         }
    }


    int main(int argc,char** argv)
    {
         int i;
         char* pValue;
         epicsShortPV nelm, nord;
         epicsWavePV wave;
         double search_timeout = 5.0;
         double get_timeout = 1.0;

         ca_task_initialize();
         casearch("file.NELM", nelm);
         casearch("file.NORD", nord);
         casearch("file", wave);
         SEVCHK(ca_pend_io(search_timeout), "casearch");


    /*ca_get(dbf_type_to_DBR(DBR_LONG),nelm.channel,(void*)&nelm.value);

    ca_get(dbf_type_to_DBR(DBR_LONG),nord.channel,(void*)&nord.value);*/

         cainfo(nelm, DBF_LONG);
         cainfo(nord, DBF_LONG);
             ca_array_get(DBR_CHAR, 10, wave.channel, (char*)&wave.value);
             SEVCHK(ca_pend_io(get_timeout), "cainfo");

         printPV(&nelm);
         printPV(&nord);
         pValue = & wave.value;
         for(i=0;i<10;i++)        printf("%d ", pValue[i]);

         ca_task_exit();
             return 0;
    }



    One thing I can't get, though everything works fine. The compiler
    goes with a warning at the line pValue = & wave.value :
    warning C4047: '=' : 'char *' differs in levels of indirection from
    'unsigned short **'

    How can it be fixed (if nesessary)?

    Thanks.




    On Fri, May 11, 2012 at 7:32 PM, Mark Rivers
    <[email protected] <mailto:[email protected]>> wrote:

        I don't have much experience with writing CA clients in C, I
        mostly use IDL, Java, Python, etc.  Perhaps someone else can help.

        Mark

        ________________________________
        From: Pavel Masloff [[email protected]
        <mailto:[email protected]>]
        Sent: Friday, May 11, 2012 9:07 AM
        To: Mark Rivers
        Cc: EPICS Tech Talk
        Subject: Re: [CA][waveform] how to NELM?

        Thanks, Mark! It works if I am reading just one PV. But when I
        am reading 2 PVs - (waveform and NELM), my NELM value is
        enormously big!!!
        How can I read several PVs?

        This is my code:

        #include <stddef.h>
        #include <stdlib.h>
        #include <stdio.h>
        #include <string.h>

        #include "cadef.h"

        int main(int argc,char **argv)
        {
            int data;         /* NELM */
            chid mychid;

            chid chan;        /* WAVEFORM - file*/
            int status;
            unsigned elementCount, nBytes, i;
            struct dbr_time_char * pTD;
            const dbr_char_t * pValue;


          SEVCHK(ca_context_create(ca_disable_preemptive_callback),"ca_context_create");

          SEVCHK(ca_create_channel("file.NORD",NULL,NULL,10,&mychid),"ca_create_channel failure");
            SEVCHK(ca_pend_io(1.0),"ca_pend_io failure");
            SEVCHK(ca_get(DBR_INT,mychid,(void *)&data),"ca_get failure");
            SEVCHK(ca_pend_io(1.0),"ca_pend_io failure");
            printf("file.NORD: %d\n",data);

            ca_clear_channel ( mychid );
            ca_task_exit ();



          SEVCHK(ca_context_create(ca_disable_preemptive_callback),"ca_context_create");
            status = ca_create_channel ( argv[1], 0, 0, 0, & chan );
            ca_search(argv[1], &chan);
            SEVCHK ( status, "ca_create_channel()" );
            status = ca_pend_io ( 1.0 );
            if ( status != ECA_NORMAL ) {
                fprintf ( stderr, "\"%s\" not found.\n", argv[1] );
                return -1;
            }

            elementCount = ca_element_count ( chan );
            nBytes = dbr_size_n ( DBR_TIME_CHAR, elementCount );
            pTD = ( struct dbr_time_char * ) malloc ( nBytes );
            if ( ! pTD ) {
                fprintf ( stderr, "insufficient memory to complete
        request\n" );
                return -1;
            }

            status = ca_array_get (DBR_TIME_CHAR, elementCount, chan, pTD );
            SEVCHK ( status, "ca_array_get()" );
            status = ca_pend_io ( 1.0 );
            if ( status != ECA_NORMAL ) {
                fprintf ( stderr, "\"%s\" didnt return a value.\n",
        argv[1] );
                return -1;
            }

            pValue = & pTD->value;
            for ( i = 0; i < 10; i++ )    printf("%d ", pValue[i]);
            printf("\nTotal size: %d\n", elementCount);
            printf("Timestamp: %d\n", pTD->stamp.nsec);
            ca_clear_channel ( chan );
            free ( pTD );

            return(0);
        }






        On Fri, May 11, 2012 at 3:42 PM, Mark Rivers
        <[email protected]
        <mailto:[email protected]><mailto:[email protected] <mailto:[email protected]>>>
        wrote:
        You can just do a ca_get of record.NELM.
        ________________________________
        From: [email protected]
        <mailto:[email protected]><mailto:[email protected]
        <mailto:[email protected]>>
        [[email protected]
        <mailto:[email protected]><mailto:[email protected]
        <mailto:[email protected]>>] on behalf of Pavel
        Masloff [[email protected]
        <mailto:[email protected]><mailto:[email protected]
        <mailto:[email protected]>>]
        Sent: Friday, May 11, 2012 6:39 AM
        To: EPICS Tech Talk
        Subject: [CA][waveform] how to NELM?

        I am writing a simple CA client in C.
        The client reads the waveform record. And I need to know how
        many elements there are in it (NELM field).
        There is a function entitled ca_element_count() which happens to
        read the NORD field.

        Does anybody know how can I get the NELM field ?



        --
        Best regards,


        Pavel Maslov, MS
        Controls Engineer at Pulsed power Lab
        Efremov Institute for Electro-Physical Apparatus
        St. Petersburg, Russia

        Mobile: +7 (951) 672 22 19
        Landline: +7 (812) 461 01 01



        --
        Best regards,


        Pavel Maslov, MS
        Controls Engineer at Pulsed power Lab
        Efremov Institute for Electro-Physical Apparatus
        St. Petersburg, Russia

        Mobile: +7 (951) 672 22 19
        Landline: +7 (812) 461 01 01




    --
    Best regards,


    Pavel Maslov, MS
    Controls Engineer at Pulsed power Lab
    Efremov Institute for Electro-Physical Apparatus
    St. Petersburg, Russia

    Mobile: +7 (951) 672 22 19
    Landline: +7 (812) 461 01 01




--
Best regards,


Pavel Maslov, MS
Controls Engineer at Pulsed power Lab
Efremov Institute for Electro-Physical Apparatus
St. Petersburg, Russia

Mobile: +7 (951) 672 22 19
Landline: +7 (812) 461 01 01


--
Matthieu Bec                GMTO Corp.
cell:  +1 626 354 9367      P.O. Box 90933
phone: +1 626 204 0527      Pasadena, CA 91109-0933


Replies:
Re: [CA][waveform] how to NELM? Pavel Masloff
References:
[CA][waveform] how to NELM? Pavel Masloff
RE: [CA][waveform] how to NELM? Mark Rivers
Re: [CA][waveform] how to NELM? Pavel Masloff
RE: [CA][waveform] how to NELM? Mark Rivers
Re: [CA][waveform] how to NELM? Pavel Masloff
Re: [CA][waveform] how to NELM? Pavel Masloff

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