Re: Homebrew STG card - IEEE 1394 firewire

[Doug Fortune <pentam-at-home.com>]

Jon Elson wrote:

> > If you wanted to consider PC ->USB->breakout box with I/O's
> > then the dirty work has already been done, and almost dirt cheap at
> >
> > http://www.ActiveWireInc.com/
> >
> > "ActiveWire-USB with programmable I/O pins that can interface to
> >   anything.  Control the pins from your browser by HTML/ javascript or
> >   VBasic or C.  Win95/98/2000, Linux, FreeBSD, LabView drivers available
> >   NOW! Macintosh next...  "

> One thing that needs to be addressed is worst-case latency on the USB, and
> using the USB drivers.  Can this really handle real-time work?  The DAC,
> PWM output, or whatever drives the servos, and whatever reads the encoders
> needs to be serviced at predictable intervals.

Ok, how about going to the next step, 100,200, or 400 Mbits/s Firewire?
a book: http://www.ercb.com/brief/brief.0065.html
Adaptec has cards and development kits:
http://www.adaptec.com/products/solutions/1394.html
http://www.whatis.com/firewire.htm  overview says

FireWire is Apple Computer's version of a new standard, IEEE 1394 High
Performance Serial Bus, for connecting devices to your personal computer. FireWire
provides a single plug-and-socket connection on which up to 63 devices can be
attached with data transfer speeds up to 400 Mbps (megabits per second). The
standard describes a serial bus or pathway between one or more peripheral devices and
your computer's microprocessor. In the next few years, you can expect to see many
peripheral devices coming equipped to meet this new standard. FireWire and other
IEEE 1394 implementations provide:

     A simple common plug-in serial connector on the back of your computer and on many
different
     types of peripheral devices
     A thin serial cable rather than the thicker parallel cable you now use to your
printer, for example
     A very high-speed rate of data transfer that will accommodate multimedia applications
(100 and
     200 megabits per second today; with much higher rates later)
     Hot-plug and plug-and-play capability without disrupting your computer
     The ability to chain devices together in a number of different ways without
terminators or
     complicated set-up requirements

IEEE 1394 provides two types of data transfer: asynchronous and isochronous. Asynchronous
is for
traditional load-and-store applications where data transfer can be initiated and an
application
interrupted as a given length of data arrives in a buffer. Isochronous data transfer
ensures that data flows
at a pre-set rate so that an application can handle it in a timed way. For multimedia
applications, this
kind of data transfer reduces the need for buffering and helps ensure a continuous
presentation for the
viewer.

The proposal then is to buy a PCI firewire card for the PC (current generations of Apples
and upcoming generations of PC's will probably have firewire already built-in), and build
a single daisy-chainable servo controller/driver board.  Up to 16 of them can be logically

chained together on a single cable,  for considerable flexibility in choosing the number
of axes.

If the data rate & latency prove acceptable, this could carry us many years into the
future...

Comments?   Flames?

Doug Fortune
pentam-at-home.com