From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4F17487C.8080508@domain.hid> Date: Wed, 18 Jan 2012 23:32:28 +0100 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <28CCC3D1EEE841E184D8E5663EBDCCBE@TerryHP> <4F171C09.8010908@domain.hid> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-help] Compile error List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Terry Fryar Cc: xenomai@xenomai.org On 01/18/2012 10:44 PM, Terry Fryar wrote: > I knew I wouldn't get enough...but I have other projects in between those > timing requirements and I wanted to see how little latency I could get. > Using an RTDM driver we wrote, I am measuring about 2us (not 20us) by > triggering an irq off a gpio and pulsing another gpio line and measuring the > difference between the irq edge and the pulsed edge using a logic analyzer. That is probably because you are not measuring latency under load. So, you do not see the worst case. > I have a board that runs a suhdol linux sbc that is somehow handling gpio > interactions within nanosecond ranges, and I have no idea how that is being > done. Even flipping a gpio pin with direct register access inside a KLM is > around 62ns. I just don't know how they are managing to detect a gpio pin > state change and respond to several things all within a couple hundred ns?? > > I've looked at their app files and it's just a gpio driver and what appears > to be a single userspace app. A mystery I guess..... I am talking about worst case here, not about average case. -- Gilles.