On Saturday 09 March 2019 14:12:43 Chris Albertson wrote:

>   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
>
Thats doing pretty good, but you're in the realm of on-offs no one else 
can fix too. I find thats the major objection to the pi, no one knows 
how it works but me.

> 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.
> >
> > > _______________________________________________
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> > > 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


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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