From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <508AA828.8050702@xenomai.org> Date: Fri, 26 Oct 2012 17:11:36 +0200 From: Gilles Chanteperdrix MIME-Version: 1.0 References: In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai] Seeking recommendations for SBC with precision timer List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Howard Lee Harkness Cc: Xenomai@xenomai.org On 10/26/2012 04:46 PM, Howard Lee Harkness wrote: > Thank you for your fast responses! > > 1) Not necessarily fanless, but that would be nice. > > 2) Don't need a timestamp. All I need is a precision interval. I want to be > able to send a signal to a device, and read a measurement exactly 11 us (or > 5 us, or 17 us, or 31 us, etc.) later, plus or minus no more than about 1 > us. <1 us precision would be better, but I think for now 1 us resolution is > sufficient. Reliably, repeatably. What you are asking is a latency of less than 1us, not a resolution. Here is a graph showing the (user-space wake-up) latencies we get with various configurations of Xenomai 2.6.1 over Linux 3.4.6 on an atom 230: http://xenomai.org/~gch/core-3.4-latencies/atom.png These are user-space wake-up latencies, you get better result with irqs handlers. But 1us, that is a bit hard. The only way I know to do this, is, for instance, if you know that the maximum irq latency is 15us, wake-up 15us before the wanted wake-up date, and spin in the timer handler until the time you want, using a clocksource which has a better resolution than 1us. x86 generally use the tsc which is such a clocksource. -- Gilles.