Minimum RTEMS system clock frequency

[Joel Sherrill]

On March 19, 2015 7:22:03 PM CDT, Chris Johns <chrisj at rtems.org> wrote:
>On 19/03/2015 8:06 pm, Alexander Krutwig wrote:
>>
>> currently I am working on the implementation of FreeBSD timecounters
>> into RTEMS as illustrated in Ticket #2271 of the developer's board
>> (https://devel.rtems.org/ticket/2271).
>
>This is really cool stuff and I think the graphs so far are excellent.
>
>> In the progress, I found out that the minimum RTEMS system clock
>> frequency should at least be 20Hz to guarantee a correct
>functionality.
>> Are there users that are troubled by this minimum system clock
>frequency?
>
>I am a little confused with the wording here.
>
>To me a 'system clock frequency' is the CPU clock or core clock or 
>something similar. Is this a frequency of the tick interrupt for RTEMS
>?
>
>If this is a tick frequency do you mean this is the maximum frequency ?
>
>A period of 50usecs is too short for any system I know of so I can only
>
>assume this is a maximum frequency and minimum period.

20 Hz is a 50 millisecond period. 

I have assumed that he meant this was the largest clock tick time quantum which is reasonable to configure.

Why is that?

>If this is a maximum frequency that seems ok with me. This is a system 
>timer and my experience is any high speed timing should use dedicated 
>timers tailored to the task, or example IEEE 1588 (PTP).
>
>Chris
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--joel