PC/104

Lennart Sorensen lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org
Tue Jul 17 12:09:07 UTC 2007


On Mon, Jul 16, 2007 at 06:25:29PM -0400, phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org wrote:
> (Disclaimer: the MPPKit is our design. It's a teaching tool and useful in
> some complete systems, but there are better choices for many
> applications.)

I just found the line on the web page 'Based on the powerful Motorola
68HC11 E1 CFN2 microprocessor' to seem rather ridiculous.  25 or 30
years ago that would have made sense.  Today it may be flexible and
useful, but I sure wouldn't call it powerful.  I am also not sure that
advertising 'over 500 sold' is actually going to help sales.  It sounds
like the thing hardly sells at all to be honest.

> The arm, mips and powerPC have a very steep learning curve, depending on
> what you're trying to do. And they are appropriate for running a complex
> program, but not for some simple control tasks.

Of course.

> For example, I recently came across a system where *everything* is
> controlled by a central PC board. This required complex multitasking
> real-time software running under Linux that was very difficult to debug.
> The genius who designed this has of course left the project.  The PC
> software included such low-level tasks as operating a stepping motor and
> detecting when a shutter is closed.

Linux wasn't designed for real time at all.  Some people try to make it
work for it, but I am not sure it will ever be a good fit for that.

> It's much better to partition the system into low-level tasks that are
> handled by microprocessors (not necessarily ours ;). The microprocessors
> then communicate with the master PC host via some sort of com link such as
> RS232 or CAN bus. So the PC issues a command to 'close the shutter' and
> then the microprocessor reports back when the shutter is closed. Very
> simple to implement and debug.

In a lot of cases people are using FPGAs to do small complex tasks which
a host PC deals with the world in general.

> In another case, the designers insisted that low-level hardware tasks be
> controlled via a PCI interface. The interface hardware is horrendously
> complicated  and is going to be a nightmare to debug. A much better
> approach would be heirarchical hardware with a PC as the master controller
> and microprocessors doing the grunt work.

PCI certainly is complex and complex to route.  It does have a lot of
bandwidth though, and a lot of supported devices and almost every modern
chipset supports it.

> A microprocessor is about $3 or less these days and anyone reading this
> could learn to program one in an hour or two.

Sure.  Very useful devices for small jobs.  I still don't consider them
powerful processors. :)

--
Len Sorensen
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