Examples

All examples below assume that there is a soft-IOC running with the following database (“db”) file:

record(calc, "counter")
# trigger everything
{
  field(PINI, "YES")
  field(SCAN, "1 second")
  field(CALC, "A+1")
  field(INPA, "counter")
}

record(waveform, "waveform")
{
  field(NELM, "3")
  field(FTVL, "DOUBLE")
}

record(compress, "buffer")
{
    field(ALG, "Circular Buffer")
    field(INP, "counter CPP NMS")
    field(NSAM, "3") # Size of the buffer
}

record(ai, "ai_buffer")
# trigger everything
{
}

record(ao, "ao_buffer")
{
  field(HOPR, 100)
  field(LOPR, -50)
  field(DRVH, 99)
  field(DRVL, -49)
  field(PREC, 3)
  field(EGU, "VOLT")
}

record(mbbo, "mbbo")
{
  field(ZRST, "VAL0")
  field(ONST, "VAL1")
  field(TWST, "VAL2")
}

Read a variable synchronously

This is an example for synchronous read. The program blocks until the value was read.

Note: This establishes a single new connection to the IOC, fetches the value and destroys the connection. Do not do this in a loop!

use Pezca;

$PV="counter";

my($err, $val)=Pezca::GetDouble($PV);
print("Err:$err Val:$val\n");

Read a variable asynchronously with a subscription (monitor)

This program sets up a monitor on the PV, then tests if there is a new value. If not, it prints a dot ‘.’. If there is a new value it fetches the value and prints it to the console.

By creating a monitor with SetMonitorDouble, the script uses an efficient way to communicate with the IOC. Each time the PV has a new value, an internal callback function stores the value in a buffer. GetDouble simply reads the value from that buffer, so this doesn’t create extra network traffic.

The internal callback function must get time to run, this is in function Delay. You must use this function for delays, do not use sleep since this doesn’t process channel access events.

use Pezca;

$PV="counter";
Pezca::SetMonitorDouble($PV);
for(my $i =0; $i<100; $i++)
  {
    if (!Pezca::NewMonitorValueDouble($PV))
      {
        print(".");
        select()->flush();
        Pezca::Delay(0.1);
      }
    else
      {
        my($err, $val)=Pezca::GetDouble($PV);
        print("Err:$err Val:$val\n");
      }
  };

Read a list variable (e.g. Waveform Record)

In the following example we read a list with length specification ranging from 0 to 4:

use Pezca;

$PV="buffer";

for(my $i =0; $i<10; $i++)
  {
    my $no= int($i/2);
    my($err, @val)=Pezca::GetList($PV, "DOUBLE", $no);
    print("No:$no Err:$err Val:@val\n");

    Pezca::Delay(0.5);
  };

Read a list variable with a monitor

In the following example we read a list variable with a monitor:

use Pezca;

$PV="buffer";

Pezca::SetMonitorDouble($PV);

for(my $i =0; $i<10; $i++)
  {
    my($err, @val)=Pezca::GetList($PV, "DOUBLE");
    print("No:$no Err:$err Val:@val\n");
    Pezca::Delay(0.5);
  };

Write a variable synchronously

This is an example for synchronous write. After write, the variable is read to show that the value was stored in the record:

use Pezca;

$PV="ai_buffer";

my $err=Pezca::PutDouble($PV, $i);
print("put $i...: Err:$err\n");
my($err, $val)=Pezca::GetDouble($PV);
print("get : Err:$err Val:$val\n");

Write a string variable synchronously

This is an example for synchronous write of a string variable. After write, the variable is read to show that the value was stored in the record:

use Pezca;

$PV="mbbo";

my $w_st;
my $r_st;

foreach my $w_st (qw(VAL0 VAL1 VAL2))
  {
    my $err=Pezca::PutString($PV,$w_st);
    print("put $w_st...: Err:$err\n");
    my($err, $r_st)=Pezca::GetString($PV);
    print("get : Err:$err Val:$r_st\n");
    Pezca::Delay(2.0);
  }

Write a list variable synchronously

This is an example for synchronous write of a list variable. After write, the variable is read to show that the value was stored in the record:

use Pezca;

$PV="waveform";

my $a= $i; my $b= $i+1; my $c= $i+2;
my $err=Pezca::PutList($PV, "DOUBLE", $a, $b, $c);
print("put $a $b $c...: Err:$err\n");
my($err, @val)=Pezca::GetList($PV, "DOUBLE");
print("get : Err:$err Val:@val\n");

Read some meta information of a record

Here we read some extra fields of a record:

use Pezca;

$PV1="ao_buffer";
$PV2="buffer";

print("Get DRVL and DRVH of $PV1.\n");
my  ($errcode,$low,$high)= Pezca::GetControlLimits($PV1);
print("err:$errcode  DRVL:$low  DRVH:$high\n");
print("\n");
print("Get LOPR: and HOPR: of $PV1.\n");
my  ($errcode,$low,$high)= Pezca::GetGraphicLimits($PV1);
print("err:$errcode  LOPR:$low  HOPR:$high\n");
print("\n");
print("Get number of elements from $PV2.\n");
my ($errcode,$no)= Pezca::GetNelem($PV2);
print("err:$errcode, elements:$no\n");
print("\n");
print("Get precision of $PV1.\n");
my ($errcode,$prec)= Pezca::GetPrecision($PV1);
print("err:$errcode, PREC:$prec\n");
print("\n");
print("Get units of $PV1.\n");
my ($errcode,$units)= Pezca::GetUnits($PV1);
print("err:$errcode, UNITS:$units\n");