From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chad Reese Subject: Re: [PATCH net-next v2 1/8] net-timestamp: explicit SO_TIMESTAMPING ancillary data struct Date: Mon, 07 Jul 2014 14:08:57 -0700 Message-ID: <53BB0C69.6000304@cavium.com> References: <1404416380-3545-1-git-send-email-willemb@google.com> <1404416380-3545-2-git-send-email-willemb@google.com> <20140705201851.GE3869@localhost.localdomain> <20140707184700.GA1610@localhost.localdomain> <53BAF8AC.6010907@cavium.com> <20140707201817.GA10683@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Willem de Bruijn , netdev@vger.kernel.org, David Miller , Eric Dumazet , Stephen Hemminger , Chad Reese , David Daney To: Richard Cochran Return-path: Received: from mail-ie0-f180.google.com ([209.85.223.180]:57705 "EHLO mail-ie0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751931AbaGGVJA (ORCPT ); Mon, 7 Jul 2014 17:09:00 -0400 Received: by mail-ie0-f180.google.com with SMTP id tr6so2233756ieb.39 for ; Mon, 07 Jul 2014 14:08:59 -0700 (PDT) In-Reply-To: <20140707201817.GA10683@localhost.localdomain> Sender: netdev-owner@vger.kernel.org List-ID: On 07/07/2014 01:18 PM, Richard Cochran wrote: > On Mon, Jul 07, 2014 at 12:44:44PM -0700, Chad Reese wrote: >> >> For Octeon, you can optionally use the hardware timestamp as the >> system clock reference. Most people don't, but it is the only way to >> get the system time to be accurate. 1588 can synchronize two Octeon >> boards to less than 1ns for the hardware timer. The Linux software >> timers is always farther off. > > Did you mean 1us ? No, it was 1ns. Who would go through all this effort if all you wanted was 1us? Our requirement was within 20ns, but me managed to get 1ns with a lab setup. We had to be careful that the scope probes used in the measurement were the same length. Chad -- Chad Reese Cavium Networks Phone: 408 - 943 - 7183 Cell: 321 - 438 - 7753