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<== Date ==> <== Thread ==>

Subject: Re: Beam Synchronous Acquistion (BSA) and the Hytec Motor Postion
From: Eric Norum <wenorum@lbl.gov>
To: "Ernest L. Williams Jr." <ernesto@slac.stanford.edu>
Cc: EPICS tech-talk <tech-talk@aps.anl.gov>
Date: Thu, 12 May 2011 11:42:54 -0700
On May 12, 2011, at 11:38 AM, Ernest L. Williams Jr. wrote:

> Mark Rivers wrote:
>>> 1ms period should be fine but I haven't
>>> checked the least time period that epicseventwait can use. Maybe Mark has better idea?
>>>    
>> 
>> That depends on the OS and how it is configured.  With vxWorks it is
>> determined by the value of sysClkRateGet/Set.  The default clock period
>> on vxWorks is normally 50/60Hz, but it can easily be increased with
>> sysClkRateSet().  If you are using RTEMS I don't know what the rate of
>> the system clock is.  Also, typically if you specify a time of X for
>> epicsEventWait the actual time will be X +- epicsThreadSleepQuantum(),
>> which is the system clock period.  In other words if I ask for 16.6 ms
>> on a standard 60Hz vxWorks system I will get 0 to 16.6 ms, because the
>> next system tick can happen immediately (=0) or we may have just missed
>> one and it will happen in 16.6ms.
>>  
> 
> Hi Mark,
> 
> Awesome, thanks for the info.
> 
> Till and Eric can you weigh in on this question for RTEMS?

>From <base>/src/RTEMS/base/rtems_config.c

#define CONFIGURE_MICROSECONDS_PER_TICK 20000

If you want a different value you can copy rtems_config.c to your application source directory, add it to the Makefile and make any changes you wish.  Note that this won't work for those of you dynamically loading your EPICS applications.

-- 
Eric Norum
wenorum@lbl.gov



Replies:
Re: Beam Synchronous Acquistion (BSA) and the Hytec Motor Postion Till Straumann

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