On Tue, Oct 25, 2016 at 9:38 PM, Nicklas Karlsson < [email protected]> wrote:
> > I think SPI runs at 500 KHz. That is 50 times slower then Ethernet if > you > > look at only the bit rate. But what matters, I think more is the time > it > > takes to send one message. It might (maybe?) be faster on SPI because > you > > avoid the TCP/IP stack. With SPI your software is driving the bare > > hardware. > > SPI on cheap micro controller run in several Mbit/second, maybe 10-20Mbit > is common. It is slower than Ethernet but there is nothing else where. > Yes they are that fast in some micro controllers. But on the "Pi" they do about 500K. I think they made some cost/performance/power trades There might be a way to make it go faster, if you have ever worked with bare ARM hardware with no OS every pin is nearly infinitely configurable but you have to understand how to program some very complex registers and this the NOT standard across all ARM chips, so you are into a 500 page manual every time. > > Sometimes a car at 55 MPH can beat a 550 MPH airplane if the trip is > short > > enough. I don't know about this case but it's kind of moot as 500KHz is > > well more than fast enough. > > I think SPI on simple device may beat Ethernet on ordinary computer then > it come to real time tasks. Capacity is a lot lower but it is available > then needed. > Yes, this was my point. I think the way it works in Linux is you get access to the port and then just push data out. With Ethernet and IP you have a few layers of software between you and the physical art. This is why I just can't believe these people worrying about latency in a switch, compared to an IP networking stack the switch is ttruely "nothing" > > > > Not sure how well SPI works on the Orange Pi. Since you've decided on > > > the 7i90HD with SPI why don't use use the Rpiwith it? > > SPI is simple stuff. It work similar to a shift register, data is clocked > in and out simultaneously. It may be possible to connect several in series > and then I think principle is similar to Ethercat although without > possibility to insert data and checksum while shifted through. > You have to read the Mesa documentation. If it wants checksums then you send them. There is no choice in this unless you want to make your own bit files > > -- Chris Albertson Redondo Beach, California ------------------------------------------------------------------------------ The Command Line: Reinvented for Modern Developers Did the resurgence of CLI tooling catch you by surprise? Reconnect with the command line and become more productive. Learn the new .NET and ASP.NET CLI. Get your free copy! http://sdm.link/telerik _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
