From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?ISO-8859-1?Q?Daniel_Gl=F6ckner?= Subject: Re: PTP_PEROUT_REQUEST and clock stepping Date: Fri, 12 Sep 2014 13:40:32 +0200 Message-ID: <5412DBB0.9010008@emlix.com> References: <54107965.6040007@emlix.com> <20140910172619.GB5944@localhost.localdomain> <20140911095245.GA5823@emlix.com> <20140912063310.GA6198@netboy> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: "netdev@vger.kernel.org" To: Richard Cochran , Christian Riesch Return-path: Received: from mx1.emlix.com ([88.198.240.195]:35858 "EHLO mx1.emlix.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753893AbaILLkf (ORCPT ); Fri, 12 Sep 2014 07:40:35 -0400 In-Reply-To: <20140912063310.GA6198@netboy> Sender: netdev-owner@vger.kernel.org List-ID: On 09/12/14 08:33, Richard Cochran wrote: > On Fri, Sep 12, 2014 at 08:24:49AM +0200, Christian Riesch wrote: >> Ok, I got it now. So you are suggesting to change the behavior of >> PTP_PEROUT_REQUEST, aren't you? And break existing applications? >> Christian I don't want to change the API. I would just have preferred a slightly different one. > I think he wants the periodic output to continue at the same phase an= d > frequency, even when you reset the clock time. >=20 > However, this is impossible to acheive because the hardware does not > support it. You mean the hardware that you know of that currently exists. I just think it is wrong to place the burden of stopping and starting the periodic output on the PTP demon. The kernel knows when clock_adjti= me and clock_settime are called and it also knows which periodic outputs are enabled and how they are configured. We just have to decide on the correct behavior (respect .start vs. ignore .start once running) to be implemented. 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. Best regards, Daniel --=20 Dipl.-Math. Daniel Gl=F6ckner, emlix GmbH, http://www.emlix.com =46on +49 551 30664-0, Fax +49 551 30664-11, Bertha-von-Suttner-Stra=DFe 9, 37085 G=F6ttingen, Germany Sitz der Gesellschaft: G=F6ttingen, Amtsgericht G=F6ttingen HR B 3160 Gesch=E4ftsf=FChrer: Dr. Uwe Kracke, Ust-IdNr.: DE 205 198 055 emlix - your embedded linux partner