Gene,

Yes, the Pi has slow I/O but this thread is about the "Blue Pill" board
that costs $2.60 with free shipping.

SO what I do is build a hybrid.   The cheap little STM32F103 has many I/O
pins that are robust and even 5 volt tolerent.   I use the STM32 to connet
to the world and then SPI to telk betwween the Pi and the STM32


Allof the I/O on the Pi is not slow.    The current version o the pi, to
Pi3B+ can do networking at 300 megabits persecond.    This is faster then
any 100BaseT device but not the 1000BaseT we would like.   None the less
fast enough

But the Pi's SPI and I2C pins on the GPIO head go DIRECT to the CPU chip,
 In fact all the lines in the 40 pin header to straight to the chip.

Back to the hybrid system.   This is thebest model and is very much like
the old PC drinving a Measa FPGA card.   A the can replace the old PC and
an STM32 ( can replace the Mesa.

Somepeople are using BeagalBone Black boards because the BBB has those
PRUs.   This is like the Pi/STM32 hybrid, logically identical.

Dn't complain about the Pi3B+.  If you are still using a 100BaseT network
switch, that switch will be the bottleneck,not the Pi.


My hybrid right not is runing real-time control at microsecond resolution
over WiFi, I have the "blue pill" device phyically near the motors then a
short cable to a Pi3 then WiFi to my Macbook. Motors are DC with 64 pulse
encoders running up to about 10,000 RPM into a 100:1 reduction gearbox.
 So we see roughtly about 10,000 encoder edges per second times two
motors in the worst case of "full speed".    The PID loops work fine even
using low-end STM32 chips





On Sat, Mar 9, 2019 at 5:33 AM Gene Heskett <ghesk...@shentel.net> wrote:

> On Saturday 09 March 2019 07:53:05 Nicklas Karlsson wrote:
>
> > > On Sat, 9 Mar 2019 at 11:59, Nicklas Karlsson
> > >
> > > <nicklas.karlsso...@gmail.com> wrote:
> > > > I think CPU Cortex-M4 is a lot slower than arduino
> > >
> > > Really? That isn't my experience. Given that the M4 is running at
> > > 120MHz and the Arduino is 8MHz and both are running the same code?
> >
> > No I got it wrong and mixed it with raspberry, I think.
> >
> The pi's huge, glaring slow i/o problem is that internal usb-2 hub. AIUI,
> only the wifi and gpio bypass that huge bottleneck.
> >
> > _______________________________________________
> > 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>
>
>
>
> _______________________________________________
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>


-- 

Chris Albertson
Redondo Beach, California

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