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On May 12, 2011, at 12:00, "Till Straumann" <[email protected]> wrote:
> On 05/12/2011 01:42 PM, Eric Norum wrote:
>> 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?
>
> Basically, the behavior is as described by Mark (i.e., the
> granularity/resolution of a blocking operation or a sleep/delay
> is determined by the OS system clock).
>
> Our GeSys images at SLAC are configured the following way:
>
> 4.9.3/rtems_p1/ssrlApps_p2
> 4.9.4/rtems_p0/ssrlApps_p3
> 4.9.4/rtems_p1/ssrlApps_p3
> 4.9.4/rtems_p1/ssrlApps_p4
>
> (and upcoming, later releases) use a system clock of 1kHz
> by default (so that we can block for less than a 360Hz
> fiducial). Only slower hardware (mvme167, uC5282, virtex,
> rce405) uses a lower clock rate of 100Hz.
>
> All older GeSys versions (not listed above) use a clock
> rate of 50Hz on all platforms.
Awesome, thanks for the info here :)
Cheers,
Ernest
>
> HTH
> -- Till
>
> PS: The increase of clock speed from the old 50Hz
> is documented in the ChangeLogs.
>
>>
>>> 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.
>>
>
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