From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=unavailable autolearn_force=no version=3.4.4 Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!news.glorb.com!peer02.iad.highwinds-media.com!news.highwinds-media.com!feed-me.highwinds-media.com!post02.iad.highwinds-media.com!news.flashnewsgroups.com-b7.4zTQh5tI3A!not-for-mail From: Stephen Leake Newsgroups: comp.lang.ada Subject: Re: Raspberry Pi, Real-Time and Ada References: <5e8fad3a-94e6-4517-af54-db8b4146803e@googlegroups.com> <858uto3cj3.fsf@stephe-leake.org> <85d2iz1g48.fsf@stephe-leake.org> Date: Sat, 08 Feb 2014 02:28:43 -0600 Message-ID: <854n4a1004.fsf@stephe-leake.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (windows-nt) Cancel-Lock: sha1:HVb1CgwIRu+QGtCY6fOq+57AiG8= MIME-Version: 1.0 Content-Type: text/plain X-Complaints-To: abuse@flashnewsgroups.com Organization: FlashNewsgroups.com X-Trace: 6640052f5eabfeef2f4a315512 X-Received-Bytes: 2763 X-Received-Body-CRC: 3636006058 Xref: news.eternal-september.org comp.lang.ada:18436 Date: 2014-02-08T02:28:43-06:00 List-Id: "Rego, P." writes: > On Friday, February 7, 2014 6:28:23 AM UTC-2, Stephen Leake wrote: >> Ok, good. >> What is your application? > > In short, drones. > >> What are your timing requirements? > For the next application I think I will need achieve 1 ms for I/O > access in hard RT, and up to 100 us for pure computation for soft RT. I don't understand; the timing for "soft RT" is stricter than the timing for "hard RT". What do "soft" and "hard" mean here? Hmm. Perhaps they just mean "hardware" and "software"; I don't see why that's a useful distinction. But you are optimizing prematurely again; these are times for small parts of the overall control cycle. You need to start from the top. How fast does the overal control cycle need to run? Once every second? 1000 times a second? For spacecraft, this is based on a stability and pointing accuracy analysis; if the control cycle were slower, the spacecraft would not be stable, or would not point accurately enough. 10 Hz is usually adequate. What does the control cycle in a drone do? I suspect the plane is basically stable by the design of the wings and tail, and the control system is just running the steering. If the drone is teleoperated, the requirement is the human sensing time; you push the joystick, you want the plane to respond "quickly". Which gives control cycle times of 0.1 seconds = 10 Hz. Although 1 second would be tolerable. If the drone is autonomous, that analysis does not apply. If the drone's mission is to take pictures of targets, you can derive timing requirements from the speed of the drone in flight and the speed of the camera. That also gives location and pointing accuracy requirements; do you have GPS on the drone? How does it know where the camera is pointed? > Indeed. Yes, I will need much faster. Based on what analysis? -- -- Stephe