Homebrew PCBs

I've always been interested in RTOS's, mostly because I'm used to
programming before the whole multitasking thing anyway.
Did you have one in mind for a usb application?
I was considering a similar process for a cheap solution for another
stepper and solenoid device(diy thermal solar).
It's possible to run usb under DOS and there are open source cnc programs.
Perhaps a patch could reroute the signals through a usb layer.
Of course this just me thinking out loud. I'd have to dig out a laptop that
had those programs on it and see if the usb dos driver causes hiccups in
the cnc program first.


On Wed, Jun 27, 2012 at 6:45 AM, Randall Morgan <rmorgan62@...> wrote:

> No, what I am describing is sending the step data not the GCode which has
> to be interpreted and compiled into step commands. It can be done using a
> RTOS but under a non RTOS it requires either extra hardware buffering.
>
> On Wed, Jun 27, 2012 at 6:34 AM, Tony Smith <ajsmith1968@...> wrote:
>
> > **
> >
> >
> > > USB can be used in an interrupt driven system. For example a timer can
> be
> > used
> > > to to generate a periodic interrupt to trigger the usb data to be sent.
> > Just as can
> > > be done with a parallel or serial port. In the case of directly driving
> > steppers the
> > > periodic time constant must be low enough or the stepper controller
> must
> > be
> > > smart enough to buffer enough incoming data to last until the next data
> > > transmission. Even smarter hardware might send an interrupt request to
> > the
> > PC
> > > to request more data to fill it's buffer.
> > >
> > > A good demo of this was done in the Windows port of EMC2 RTS. Here a
> > > Windows XP, Vista, or 7 host uses the USB port to send data to a PIC uC
> > to
> > be
> > > buffered. The step data is then used to drive the motor steps. The data
> > transfer
> > > rate is plenty high enough but the period between transfers is the
> issue.
> > Under
> > > Linux, USB can be accessed at a lower level then under Windows and
> > results
> > in
> > > lower transmission latency.
> > >
> > > Playing Devil's advocate I'd say that RTOSs in uC devices can and do
> > provide
> > > almost identical access to hardware USB as they do to parallel
> ports....
> > But on
> > > the PC level you are right in that the OS allows much lower level
> access
> > to the
> > > para port.
> >
> > That's the grumble people have, USB isn't as simple as parallel. The
> > hardware your describing already exists (Smoothstepper, Flashcut etc),
> and
> > there are even Ethernet versions. Some people even use Arduinos for that.
> >
> > The PC just dumps the g-code to the hardware, and the hardware controls
> the
> > mill, not the PC. That's the way CNC used to be, with g-code drip-fed via
> > RS-232.
> >
> > The basic point is that direct control of CNC via USB isn't feasible, the
> > messaging stack introduces delays that makes it unreliable. Window,
> Linux,
> > Mac; they've all got the same problem.
> >
> > Even if it does work ok, someone plugs in something extra... and the OS
> go
> > off to handle that.
> >
> > Some people just don't like having to spend an extra $300 when the
> parallel
> > port works just fine.
> >
> > Tony
> >
> >
> >
>
>
>
> --
> If you ask me if it can be done. The answer is YES, it can always be done.
> The correct questions however are... What will it cost, and how long will
> it take?
>
>
> [Non-text portions of this message have been removed]
>
>
>
> ------------------------------------
>
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>
>
>
>


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