From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Mike Frysinger" Subject: Re: Some embedded topics Date: Thu, 29 May 2008 00:21:52 -0400 Message-ID: <8bd0f97a0805282121j10a99bb7ve92efc6a8dc8bbb1@mail.gmail.com> References: <483C83DE.3040604@cisco.com> <8bd0f97a0805271527i622a31b8t68ba24c80a2e034a@mail.gmail.com> <20080527223142.GU26837@email.mot.com> <200805282201.48746.rob@landley.net> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; bh=dWtYXgRSCcgd6OIMOMIbWPQeYyNAE3gY/SdYzCX7ieQ=; b=Jc67NdtlMsiFI88hS7AHNaLYdNqZdkJI9/R0Sfcb4ej28w2jsRZY+tw6xfq5nA+IPL+Ok5QQ34kOrSXSdg0dG8yfbquARr4bHULbi67Mser2Sf9J6DEeBdEWaxyqJGlHz8KMNGRnfhiK7nmmkBaG9s2uYyX/amuwbtSpXYhMvAQ= In-Reply-To: <200805282201.48746.rob-VoJi6FS/r0vR7s880joybQ@public.gmane.org> Content-Disposition: inline Sender: linux-embedded-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Rob Landley Cc: T Ziomek , David VomLehn , linux-embedded-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On Wed, May 28, 2008 at 11:01 PM, Rob Landley wrote: > On Tuesday 27 May 2008 17:31:42 T Ziomek wrote: >> If I understand correctly David is talking about logging some trace-like >> info (so it exists before a HW watchdog expires), and having it somewhere >> "safe" from being disturbed by a HW reset. > > The standard way of doing this is to use the mem= kernel command line > parameter to tell the system it has less memory than it does, and using > what's left as a ramdisk. Years ago I saw some userspace thing running as > root mmap() /dev/mem (or whatever they're calling it these days) and log to > it. In theory you could even set the dmesg buffer up at the end of physical > memory with a smallish kernel patch, make it big, and set the kernel to doing > verbose printks. > > The trick is A) knowing the absolute physical address at which your debug > buffer lives so you can find it after the reboot, B) convincing the system to > do something useful with it on reboot rather than just overwriting it with > fresh log data. how about the fact that when the core resets, the memory controller is often reset as well ? that external memory is going to degrade. or do we just bite our thumb and weather the few random bit errors ? -mike -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html