Latency does not matter if the real-time timing is done on the "far end". N the case where you would use USB or Ethernet you'd have a processor, either an FPGA or a uP. If there is any kind of buffer or memory on the processor then millisecond hang-ups are OK.
Proof that this works is with al the machine tools that in fact use these kinds of links. Or just look at anyone who is using an Ethernet connected Mesa card with LinuxCNC. You'd be correct if the far end device was just a dumb serial connected parallel port and all the timing was generated on the PC. On Tue, Oct 17, 2017 at 10:25 AM, Peter C. Wallace <p...@mesanet.com> wrote: > On Tue, 17 Oct 2017, Chris Albertson wrote: > > Date: Tue, 17 Oct 2017 10:02:09 -0700 >> From: Chris Albertson <albertson.ch...@gmail.com> >> Reply-To: "Enhanced Machine Controller (EMC)" >> <emc-users@lists.sourceforge.net> >> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> >> Subject: Re: [Emc-users] Pine64 / Rpi3 >> >> On the Pi the Ethernet and USB are on the same shared bus. But >> how much bandwidth is required to drive a Mesa FPGA card? I >> have read the Ethernet port can only push about 40% of it's spec'd >> bandwidth but the card only requires 2% it's OK. >> >> If performance is the goal you's spend an eatery $50 and buy an >> Intel PC mainboard rather than the Pi. >> >> >> > > Performance is not the issue, latency with USB drivers is the issue. > USB or USB Ethernet have plenty of performance, but suffer from occasional > multi-millisecond latencies. These are fine for normal network usage > but not good for LinuxCNCs real time I/O. > > There are some RPI form factor boards that do have Ethernet built into the > SOC > which might be suitable for real time Ethernet. > > > On Tue, Oct 17, 2017 at 9:56 AM, andy pugh <bodge...@gmail.com> wrote: > > On 17 October 2017 at 17:51, Greg Bentzinger <skullwo...@yahoo.com> wrote: >> >> > Using >> > these boards Ethernet port as a dedicated port is an option, >> >> I don't think it is. I have heard that the Pi Ethernet port is on the USB >> bus. >> >> -- >> atp >> "A motorcycle is a bicycle with a pandemonium attachment and is >> designed for the especial use of mechanical geniuses, daredevils and >> lunatics." >> яя George Fitch, Atlanta Constitution Newspaper, 1916 >> >> ------------------------------------------------------------ >> ------------------ >> Check out the vibrant tech community on one of the world's most >> engaging tech sites, Slashdot.org! http://sdm.link/slashdot >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users >> >> > > > -- > > Chris Albertson > Redondo Beach, California > ------------------------------------------------------------ > ------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > Peter Wallace > Mesa Electronics > > (\__/) > (='.'=) This is Bunny. Copy and paste bunny into your > (")_(") signature to help him gain world domination. > > ------------------------------------------------------------ > ------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > -- Chris Albertson Redondo Beach, California ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
