Re: [CA][waveform] how to NELM?

[Pavel Masloff <pavel.masloff@gmail.com>]

 I have tried to solve it using the Primitive C Data Type :

typedef struct {
    chid channel;
    int status;
    long number;
    dbr_char_t value;   
} epicsWavePV;

....

int main(int argc,char** argv)
{ 
   const dbr_char_t* pValue;
   epicsWavePV wave;
   ......
   ca_array_get(DBR_CHAR, 10, wave.channel, &wave.value);
   ......
   pValue = &wave.value;
   for(i=0;i<10;i++)        printf("%d ", pValue[i]);
}

And it compiles and runs (now without error during compilation) on Windows.
I then compile it on Linux. Compilation no errors. Run and get: Segmentation fault.
It seems I have to allocate memory for my wave structure (as in CA reference manual http://www.aps.anl.gov/epics/base/R3-14/12-docs/CAref.html#Channel). 
My program, though, is partially based upon Dirk's caTutorial. 

Strange, strange... Are there any C clients programmers out there?

Pavel.

On Sat, May 12, 2012 at 11:27 AM, Pavel Masloff <pavel.masloff@gmail.com> 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 <pavel.masloff@gmail.com> 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 <rivers@cars.uchicago.edu> 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 [pavel.masloff@gmail.com]
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 <rivers@cars.uchicago.edu<mailto:rivers@cars.uchicago.edu>> wrote:
You can just do a ca_get of record.NELM.
________________________________

From: tech-talk-bounces@aps.anl.gov<mailto:tech-talk-bounces@aps.anl.gov> [tech-talk-bounces@aps.anl.gov<mailto:tech-talk-bounces@aps.anl.gov>] on behalf of Pavel Masloff [pavel.masloff@gmail.com<mailto:pavel.masloff@gmail.com>]

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

-- 
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