Re: EZ-USB

--- In CAD_CAM_EDM_DRO@y..., Chris Stratton <stratton@m...> wrote:

> Seperation in USB busses is a relative thing. The computer may have
> multiple jacks, but they all ultimately hang off the same controller
> chip. Mess with that chip and you loose all the USB devices. I

think

> my preference would be to have the CNC controls be the only USB
> devices in the system - that way under something like rtlinux, you
> could leave the USB driver out of the main kernel, so that only the
> realtime portion of the system could talk to the controller. Of
> course things may get harder when all keyboards and mice are USB...

Yes the busses share one controller chip, but software problems
in one USB device driver are less likely to bring all USB traffic
to a halt. Running the USB controller chip is a major task, one
that I feel is best left to the operating system which has lots
of debug time on it, instead of code written just for our needs
which would have a comparatively small user base.

> Stepper systems have a unique advantage in that they don't move
> without constant input. A servo or hardware pulse generator can

lead

> to a runaway. At a minimum, I think you need to be protected

against

> computer crashes and microcontroller crashes. A typical embedded
> systems trick is a timer that will reset the processor if it is not
> periodically set back to 0. Having it also trigger someting like an
> Estop that cuts power to the drives would be a good idea, just
> in case the micro can't recover.

The planned dead man timer would indeed inhibit output pulses and
activate a signal which could be used to disable other external
hardware.

Steve Stallings