Experimental Physics and
Industrial Control System

Dylan Maher Loughnan <[email protected]> · Wed, 5 Feb 2003 16:26:03 -0500 (EST)

Hello,
	I am  experimenting with EPICS base R3.14.1. running it on a 
standard RedHat7.3 machine. I have written device support for a few NI DAQ 
cards, which is going very well. In doing so, I noticed something 
strange.  The scan period seems to be consistently extended by an 100th 
of a second, when using device support.  I first noticed this when 
I toggled a binary out at 10Hz to generate a square wave.  I saw the 
effect very clearly on the oscilloscope.
	I then had a look at the time-stamps and saw the same thing.  To 
see if this was due to device support, I built an example with device 
support that did nothing.

static long Inuit_bo();
static long write_bo();
struct {
	long		number;
	DEVSUPFUN	report;
	DEVSUPFUN	init;
	DEVSUPFUN	init_bo;
	DEVSUPFUN	get_ioint_info;
	DEVSUPFUN	write_bo;
}devBoDIO96={	5,NULL,NULL,init_bo,NULL,write_bo,};

static long init_bo(pbo)
    struct boRecord	*pbo;
{
 return(0);
}
static long write_bo(pbo)
    struct boRecord	*pbo;
{ 
    return(0);
}

like so.  
The scan rate was set to .1 and the same problem occurred.

Here is the ca-monitor with empty device support

 DML:Bo0                        02/05/03 16:06:27.070044  
 DML:Bo0                        02/05/03 16:06:27.280062  
 DML:Bo0                        02/05/03 16:06:27.490039  
 DML:Bo0                        02/05/03 16:06:27.700034  
 DML:Bo0                        02/05/03 16:06:27.910037  
 DML:Bo0                        02/05/03 16:06:28.120074  
 DML:Bo0                        02/05/03 16:06:28.330045  
 DML:Bo0                        02/05/03 16:06:28.540051  
 DML:Bo0                        02/05/03 16:06:28.750047  
 DML:Bo0                        02/05/03 16:06:28.960049  

Using soft records, there is no such problem.

Has anyone else noticed this? 
any help would be greatly appreciated

best regards.

Dylan Maher-Loughnan
MIT-Bates Linear Accelerator Center

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System