Re: [CAD_CAM_EDM_DRO] Re: EZ-USB

Chris Stratton wrote:

> > DOS is not a reasonable avenue for USB work, but Linux and
> > Macintosh both support USB.
> >
>
> There have been several mailing lists posts hinting at the existence
> of USB for rtlinux, but nothing definite at either rtlinux.org or
> rtlinux.com
>
> As I understand it, it is not enough for the linux kernel to be able
> to talk USB. Rather, the realtime code that runs above the kernel and
> hence can't use the kernel's drivers, is what needs to talk to the I/O
> device.

Yup, at least for EMC, it would have to be real-time, and the kernel would have
to leave that USB port completely alone. (That might help reliability, though.)

> Another option would be to port the the reatlime portion of EMC to
> actually run on the USB microcontroller and have the non-realtime
> portions (which run under the linux kernel and can use its drivers)
> feed data to the USB micro rather than to a local realtime task. The
> micro may not be fast enough to do this... but there might be one that
> is, especially if a seperate unit was used for each axis. Want to add
> a rotary table to your mill? just buy it, plug its integrated driver
> into the USB, and watch it enumerate!

If you use separate micros, then you have to keep all axes synchronized.
Not so easy.

> In my opinion, one of the really good things about EMC is that it is
> open to modification. A USB device that used code downloaded at
> runtime and built with gnu development tools would preserve this,
> although with a sharper learning curve given the need to know 8051
> assembly.

This is the wonderful thing about EMC, there is no assembly code in there.
(Actually, there is just the tiniest bit, there are C macros that put 80x86
input and output instructions inline with the code, avoiding subroutine
calls.) Also, all calculation, all the way through, is done in floating point,
making the arithmetic a lot simpler, but not so easy for an 8-bit micro.

Jon