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=-0.3 required=5.0 tests=BAYES_00, REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4 Path: border1.nntp.dca1.giganews.com!nntp.giganews.com!goblin2!goblin.stu.neva.ru!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: silly ravenscar question Date: Wed, 25 Feb 2015 18:55:51 +0100 Organization: cbb software GmbH Message-ID: <14r7a7x3kyv4t.13luzs6ukxqiq$.dlg@40tude.net> References: <8e30f54c-81c4-4861-897c-bb6c563c76e8@googlegroups.com> Reply-To: mailbox@dmitry-kazakov.de NNTP-Posting-Host: w2sqUGEBZqsVBYNL7Ky3Kg.user.speranza.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset="big5" Content-Transfer-Encoding: 8bit X-Complaints-To: abuse@aioe.org User-Agent: 40tude_Dialog/2.0.15.1 X-Notice: Filtered by postfilter v. 0.8.2 Xref: number.nntp.giganews.com comp.lang.ada:192346 Date: 2015-02-25T18:55:51+01:00 List-Id: On Wed, 25 Feb 2015 09:35:26 -0800 (PST), jan.de.kruyf@gmail.com wrote: > On Wednesday, February 25, 2015 at 12:45:53 PM UTC+2, Dmitry A. Kazakov wrote: > >> The high end is 8 analogue channels 100µs over the network + hundreds of >> lower speed channels. Data volumes is not a big problem. E.g. we can sample >> 8 100µs channels and distribute them over the network without data loss, >> doing 10ms oversampling. > > What is '100µs ' ? '0xc79b9c' was nowhere to be found. micro > what do you mean to say by 10msec oversampling? That would be to store each 100 values into the buffer and get the wave-form each 10ms. Normally, high-speed channels are not used for control, it means that we don't need to react each 0.1ms, but we must catch each value, stamp it and pass further, e.g. to the data logger or to the software oscilloscope. > in any case to focus the thinking, I did some quick sums: > A packet with a payload of 50 bytes, according to the theory should be > able to do the roundtrip (100 m cable, 1 switchbox, no packet contention) > in 25 usecs through an stm34 board, with time to spare. that includes DMA > and offloading and onloading of data. > So that makes 40 packets per msec. Leave some space for syncframes, arp > frames and data loss, then 20 roundtrip packets /msec should be doable, > provided the jitter is strictly controlled. > An individual terminal has all the time in the world to handle the data > between commframes, but I bet that, depending on what you want out of the > system, the pc might feel the strain at that rate. (and the rt scheme must > be up to scratch in the pc) We managed 0.2ms with 4 channels without oversampling, transported over XCP under VxWorks. XCP is a UDP-based protocol. The data were coalesced into one frame. > So the bottleneck according to me is in the pc in most cases. This is true. > In any case so according to your specs we would need some kind of > multiplexing scheme. This is one case when you trade latencies for throughout. In other cases latencies are more important, e.g. for control and for time synchronization. The latter is the weakest spot of all existing field buses. Most of them do not have any, others have a garbage clock synchronization, like EtherCAT's distributed clock is. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de