From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from bh-25.webhostbox.net ([208.91.199.152]:37280 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752304AbbGANy3 (ORCPT ); Wed, 1 Jul 2015 09:54:29 -0400 Message-ID: <5593F10D.5000507@roeck-us.net> Date: Wed, 01 Jul 2015 06:54:21 -0700 From: Guenter Roeck MIME-Version: 1.0 To: Ariel D'Alessandro CC: linux-watchdog@vger.kernel.org, wim@iguana.be, ezequiel@vanguardiasur.com.ar Subject: Re: [PATCH 1/2] watchdog: NXP LPC18XX Windowed Watchdog Timer Driver References: <1435343072-8753-1-git-send-email-ariel@vanguardiasur.com.ar> <1435343072-8753-2-git-send-email-ariel@vanguardiasur.com.ar> <20150626190700.GC23078@roeck-us.net> <55903943.10309@vanguardiasur.com.ar> <5590CDF6.7000103@roeck-us.net> <5593CF3F.9040206@santafe.gov.ar> <5593D6CC.10201@vanguardiasur.com.ar> In-Reply-To: <5593D6CC.10201@vanguardiasur.com.ar> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-watchdog-owner@vger.kernel.org List-Id: linux-watchdog@vger.kernel.org On 07/01/2015 05:02 AM, Ariel D'Alessandro wrote: > (Sorry, I sent the last mail with an incorrect mail account) > > El 01/07/15 a las 08:30, adalessandro escibió: >> >> El 29/06/15 a las 01:47, Guenter Roeck escibió: >>> On 06/28/2015 11:13 AM, Ariel D'Alessandro wrote: >>>>>> +/* Timeout values in seconds */ >>>>>> +#define LPC_WDT_DEF_TIMEOUT 1 >>>>>> + >>>>> >>>>> One second ? This is highly unusual. 30 or 60 seconds is more common, >>>>> and one second would be very challenging for user space. >>>>> >>>>> Any special reason for using such a tight default ? >>>> >>>> Considering that LPC18xx Watchdog has a fixed divide-by-4 clock >>>> pre-scaler and a 24-bit counter and that Watchdog clock runs at a fixed >>>> frequency of 12MHz, timeout range goes from 1 to 5 seconds. >>>> >>>> I think you're right, 1 sec is very challenging, so it's 5 secs then. >>>> >>> Ultimately you might want to consider a soft timer as backup to the system >>> timeout. But that can be done later if/when needed. >> >> I understand your point, but just to be sure, what do mean by soft timer? >> A kernel function which pings the watchdog periodically even if the watchdog is open. Example: Timeout is set to 30 seconds. Since the HW watchdog times out earlier than that, it needs to be pinged regularly (eg every 2.5 seconds). The kernel does that with a timer unless user space does not ping the watchdog within the configured interval of 30 seconds. Guenter