EPICS Channel Access Overview

Interface with ca_repeater (connection management)
```
ca_add_exception_event
```
Specifies a callback routine that is called when ca detects problems
```
{ Other Code }
ca_task_exit
```
Release all resources allocated by channel access.

Search

ca_search_and_connect(name,pchid,connectionCallback,userarg)


ca_replace_access_rights_event(chid,accessRightsCallback)

Above calls buffered until buffer full or ca_pend or ca_flush.
UDP broadcast
Each IOC on subnet receives each udp packet
TCP connection established to each IOC that has any channels.
connectionCallback called whenever connection status changes.
accessRightsCallback called whenever access rights changes.
Given a chid you can always retrieve userarg.

Puts

ca_array_put(type,count,chid,pvalues)
. . .
ca_flush_io()

Calls are buffered until buffer full or ca_flush or ca_pend.

ca_put_callback(type,count,chid,pvalue,putCallback,userarg)

putCallback called after all record processing resulting from put completes.

Gets

ca_array_get(type,count,chid,pvalues)
. . .
ca_pend_io(timeout)

ca_array_get_callback(type,count,chid,getCallback,userarg)
. . .
ca_pend_event(timeout)

Monitors

ca_add_masked_array_event(type,count,chid,eventCallback,user
arg,pevid,mask)

Call this once for each channel to be monitored.
Mask allows value changes, alarm changes, archival changes

ca_pend_event(timeout)

Waiting

ca_flush_io

Normally called by ca_pend routines
Sends any udp/tcp buffers that are not empty
```
ca_pend_io(timeout)
```
Calls ca_flush_io
Waits until timeout OR until all outstanding ca_gets satisfied
Also waits until ca_search with no callback are satisfied
```
ca_pend_event(timeout)
```
Waits for timeout processing events as they happen
```
timeout
```
0 - Wait forever
Short timeout, e.g. .0001 (seconds) is acceptable but DON'T hog CPU.

CA with X

Channel Access uses `select' to wait.
File Descriptor Manager can be used.
Channel access provides ca_add_fd_registration
X provides similar call

ezCa - Easy Channel Access

Goals
- Easy to use.
- Provide non-callback synchronous model.
Requirements
- Group of about 6 people developed requirements.
- Basic requirement was that brief description should be about one page
  - eaca.h is one page!!!
- Support for synchronous groups and individual requests.
- Pass channel names, auto search, easy error handling.

Data Types

ezcaByte
ezcaString
ezcaShort
ezcaLong
ezcaFloat
ezcaDouble

Basic Calls

int ezcaGet(pvname,  type,  nelem, buff)
int ezcaPut(pvname,  type,  nelem, buff)
int ezcaGetWithStatus(pvname,type,nelem,buff,time,stat,sevr)

Synchronous Groups

int ezcaStartGroup(void)
  [... any combination of get and put ...]
int ezcaEndGroup(void);

Error Handling

ezcaPerror(message)
ezcaGetErrorString(message,errorstring)
ezcaFreeErrorString(errorstring)

Other Groupable Functions

int ezcaGetControlLimits(pvname,type,low,high)
int ezcaGetGraphicLimits(pvname,type,low,high)
int ezcaGetNelem(pvname,nelem)
int ezcaGetPrecision(pvname,precision)
int ezcaGetStatus(pvname,time,stat,sevr)
int ezcaGetUnits(pvname,units)

Monitor Functions

int ezcaSetMonitor(pvname,type)
int ezcaClearMonitor(pvname,type)
int ezcaNewMonitor(pvname,type)

Other Functions

void ezcaAutoErrorMessageOff()
void ezcaAutoErrorMessageOn()
int ezcaDelay(seconds)
int ezcaGetRetryCount()
int ezcaSetRetryCount()
float ezcaGetTimeout()
int ezcaSetTimeout(seconds)

Escape to Channel Access

ezcaPvTochid(pvname,chid)

Example Program

/*example.c*/
/*From stdin read a list of pvnames. Get each as a double*/
#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <cadef.h>
#include <tsDefs.h>
#include <ezca.h>
#define MAX_PV 1000
#define MAX_PV_NAME_LEN 40
main()
{
    int    npv=0;
    double    *pdata;
    char    *pname[MAX_PV];
    int    status;
    int    i;
    char    tempStr[MAX_PV_NAME_LEN];
    char    *pstr;
    while(1) {
      if(npv >= MAX_PV ) break;
      pstr = fgets(tempStr,MAX_PV_NAME_LEN,stdin);
      if(!pstr) break;
      if(strlen(pstr) <=1) continue;
      pstr[strlen(pstr)-1] = `\0'; /*strip off newline*/
      pname[npv] = calloc(1,strlen(pstr) + 1);
      strcpy(pname[npv],pstr);
      npv++;
    }
    pdata = (double *)calloc(npv,sizeof(double));
    ezcaStartGroup();
    for(i=0; i<npv; i++) {
      status = ezcaGet(pname[i],ezcaDouble,1,(void *) &pdata[i]);
      if(status) {
          ezcaPerror("ezcaGet");
          break;
      }
    }
    status = ezcaEndGroup();
    if(status) ezcaPerror("ezcaEndGroup");
    for(i=0; i<npv; i++) {
      printf("%s %f\n",pname[i],pdata[i]);
    }
    return(0);
}

EPICS Channel Access Overview

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