From mboxrd@z Thu Jan 1 00:00:00 1970 From: Philippe Gerum In-Reply-To: <4D469437.9050902@domain.hid> References: <1296469933.2214.35.camel@domain.hid> <4D469437.9050902@domain.hid> Content-Type: text/plain; charset="UTF-8" Date: Mon, 31 Jan 2011 11:53:54 +0100 Message-ID: <1296471234.2214.38.camel@domain.hid> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-help] Is xenomai OK for early boot purpose ? List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: xenomai@xenomai.org On Mon, 2011-01-31 at 11:51 +0100, Gilles Chanteperdrix wrote: > Philippe Gerum wrote: > > On Mon, 2011-01-31 at 09:55 +0100, gryma biloy wrote: > >> Hello, > >> > >> On a project running Linux on a beagle board, I'd like to add the > >> following capabilities to my platform : > >> - real time processes with periodic tasks (10ms, 100ms & 200 ms) and > >> a low jitter (< 50 us) > > > > Kernel space apps then, likely. Userland apps (the recommended way) > > probably have a larger worst-case jitter on this hardware, albeit still > > below 100 us. Gilles? > > Las time I checked, latency measured on a 720MHz omap3 was around 55us > with a 1ms period and 35us with a 100us period. Yeah, I suspect that longer periods ( >= 10 ms ) may introduce more opportunities for cache eviction due to linux activity, and therefore higher jittery, even if bounded. > > > > >> - early boot operations (i.e. being able to perform some tasks asap > >> after a power on reset) > >> > >> I've searched for solutions over the net and Xenomai seems to be a > >> possible candidate to fulfill > >> these constraints. Can you please share your knowledge to confirm that > >> Xenomai would make > >> the job (especially on the early boot side) ? > >> > > > > I don't see how Xenomai could directly help in any way for the early > > boot goal. If you question is about whether Xenomai initializes fast > > enough, and early enough during the linux boot process for kicking rt > > applications as soon as possible, then the answer is yes, that should > > do. > > Well, user-space applications will not get started before user-space is > started, i.e. basically before root filesystem has been mounted and init > is running. You could write your real-time application as the init > application, but that would be kind of awkward. > -- Philippe.