Experimental Physics and
Industrial Control System

On Linux, that function uses essentially '1.0 / sysconf ( _SC_CLK_TCK )'. The sysconf value is usually 100 (Hz), and it would explain why EPICS thinks it won't achieve the desired scan rate. I don't think a modern kernel will actually be limited by its tick rate, so I don't know how accurate that heuristic is.

 

Either way, the 'period' value isn't touched after this verification, so I think the IOC will still attempt to use it. You could try running a simple counter in your SCAN and checking with camonitor if the 100Hz rate is actually achieved.

 

I think scanppl() might have trouble detecting overruns with a period of 0.01, though:

 

        if (period > 0.0 &&
            (fabs(period - ppsl->period) > 0.05))
            continue;

 

By the way, epicsThreadSleepQuantum() can return 0.0 if the sysconf errors out, which I believe would result in a SIGFPE in initPeriodic() when dividing by quantum.

 

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