What makes SPI nice is not it's speed. On the Pi it can go up to 250 MHz, so Ethernet beats it for speed and Ethernet cables can be 100 meters long. SPI wins because it is fast enough for most things and is very simple, just connect the wires. But it only works over a short distance. But it is SIMPLE, conceptually no unlike TTL level serial.
Ethernet needs some support hardware, a small transformer at least. Unlike simply using GPIO pins, SPI does not need much CPU time to send data. But if writing software you should not have to decide of lock in a certain communications method. I like whatht ehauthors is ros-serial did, that w=said "Use any communications method that has these four fuctions: open, close, read, write. THat pretty much means anything from a network socket to an RS232 cable. On Wed, Mar 27, 2019 at 6:15 AM Gene Heskett <ghesk...@shentel.net> wrote: > On Wednesday 27 March 2019 08:12:48 TJoseph Powderly wrote: > > > ( list apology, I seem to have replied to posters rather than to the > > list, and several times :-( > > > > re SPI comms Linuxcnc SBC microcontrollers ... > > > > it has been said on this mail list, > > that SPI is a good candidate for a bus technology to work _with_ > > realtime. > > > > heres some work in that vein (maybe overlooked) > > > > yeltrow's work: > > a generic spi hal module so you can use other SPI devices ( rpi, > > arduino, mcp23s17, ENC28J60, theres a lot of spi stuff to hang onto > > such a bus ) > > https://www.forum.linuxcnc.org/24-hal-components/28851-spi-bus-generic > >-driver-and-st-l6480 > > > Interesting driver for the big stuffs. However, I wonder if yeltrow is > aware of rpspi.ko, now part of LCNC. Not parport based but gpio, > written specificly for the rpi3b. And I'm using it, writing to a Mesa > 7i90 at 42 megabaud, and reading back from the 7i90 at 25 megabaud > useing only 4 gpio pins for 2 or 3 target devices. > > Perusal of that code might be of help to yeltrow. gpio seems to be about > 10x faster than trying to simulate SPI over a parport. The 7i90 has > both modes depending on the firmware loaded. > > > the files are on the forum for members linuxcnc-upload-2015-12-03.tar > > So this work handily predates rpspi.ko. Still, theres obviously things to > be learned from the rpi version. > > > erste's work: > > for ethernet circumventing usb ( via spi > > interesting as spi and ethernet seem to be future avenues > > http://erste.de/ethraw/README > > > > theres other efforts but less coupled to the spi grail > > > > tomp > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > Cheers, Gene Heskett > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
