On Mon, Jan 31, 2011 at 11:53 AM, Philippe Gerum <[email protected]> wrote: > 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.
Does this mean that the main reason for jittery is due to the cache ? What would be the other reasons, if any ? >> >> - early boot operations (i.e. being able to perform some tasks asap >> >> after a power on reset) >> >> >> > >> > 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. Understand. I will make a try a see if I can meet some of my constraints. Thanks for your replies, -- Gryma _______________________________________________ Xenomai-help mailing list [email protected] https://mail.gna.org/listinfo/xenomai-help
