Re: Newbie Question About Device Drivers

From: Phil Barila (PBarila_at_Barila.com)
Date: 08/03/04 

Date: Mon, 2 Aug 2004 21:14:55 -0600

"TerryW @vbssys.com>" <prog<NOSPAM> wrote in message
news:3fksg09thsgrhetcj9628e0mvgr3ffdbq2@4ax.com...
> Thanks for the Post Mr. Burn.
> I guess we are trying to achieve a more "Real Time" operating system.
> We build an XP embedded operating system and then deploy it. This
> works great for a lot of our applications. But for some of our
> applications, it is very critical that we monitor things flawlessly.

All together now! "Windows is not an RTOS". Realtime extensions can help,
but it's better to architect around the non-realtime nature if you can.

> We have an advantech card that we put on a PCI slot that we use for
> physical Digital IO (turning gates on/ checking for photo-eye states)
> for some systems it is imperitive that we NEVER miss a state change
> for an input. And some inputs cycle at 50 cycles per second. We
> notice that during intensive screen activity we miss pulses when using
> just C++ to read the address of the input card.

Do you need to do anything in response to the state cahnge, or do you just
need to know it happened? How tight is the latency requirement from state
change to response, if there is one?

> It would be ideal to have a piece of code that just counts how many
> times the state has changed and return it to other pieces in shared
> memory or on the socket.

Have your hardware do that. Then you can read the count at your leisure.

Phil 

-- 
Philip D. Barila  Windows DDK MVP
Seagate Technology LLC
(720) 684-1842
As if I need to say it:  Not speaking for Seagate.
E-mail address is pointed at a domain squatter.  Use reply-to instead.