netdev - Re: PTP_PEROUT_REQUEST and clock stepping

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Date:	Fri, 12 Sep 2014 17:19:29 +0200
From:	Daniel Glöckner <dg@...ix.com>
To:	Richard Cochran <richardcochran@...il.com>
CC:	Christian Riesch <christian.riesch@...cron.at>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: PTP_PEROUT_REQUEST and clock stepping

On 09/12/14 16:40, Richard Cochran wrote:
>> Taking the Intel i210 as an example, the third option (doing nothing)
>> would lead to the following behavior:
>>
>>  - If the clock is stepped back, the periodic output stops until the
>>    clock reaches the point when it was adjusted.
>>
>>  - If the clock is stepped forward, the periodic output oscillates at
>>    62,5 MHz to catch up.
> 
> That is a good example of "the results are undefined".
> 
> So, how would you reprogram the i210 to keep the period output
> continuous?

0. I'm assuming here that new_time >= start
1. stop the periodic output via TSAUXC
2. set the clock via SYSTIM* to new_time
3a. if (new_time - start) % period < period / 2
	set the TRGTTIM* regs to new_time - (new_time - start) % period
3b. else
	set the TRGTTIM* regs to new_time - (new_time - start) % period
	                                  + period
4. start the periodic output via TSAUXC

Best Regards,

  Daniel

-- 
Dipl.-Math. Daniel Glöckner, emlix GmbH, http://www.emlix.com
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