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Realtime and WinNT

Posted on 2000-03-10
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Last Modified: 2013-11-20
I'm currently developing an application under NT, which periodically sends data to the parallel port every 50 ms with a tollerance of max +/- 125ms.

I tried several ways to implement this with Multimedia Timers and with own threads with highest thread priority.

But in some (bad) cases, events do not apeare for 2,5 seconds.

Are there solutions do solve this problem? Or do I have to write VxD's to take control of this realtime problem???
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Question by:Coma
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by:jhance
ID: 2604426
VxDs are not an option under NT since these are a Win9x feature only.  A device driver is one possibility but remember that NT itself is NOT a RTOS (Real Time Operating System).  An RTOS (like VRTX, VxWorks, pSOS, and others) guarantee a certain latency.  NT doesn't do this so, literally, it's response to an event can take forever.

Your requirement of 50mS +/- 125mS might be achievable, however, with a device driver.  Of course, I'd be really careful with the - 125mS side of the tolerance....

The remaining problem here is that NT doesn't guarantee that even a device driver will get serviced under all circumstances.  If another device driver has control of the system, NT cannot give control to your driver until the one with control gives it up.  If this is a critical situation you might consider a hardware assist solution where it can continue to operate for a reasonable period without any software attention.  Another possibility is one of the NT add-ons that run underneath NT and provide real-time services in an NT environment.
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Author Comment

by:Coma
ID: 2604587
Tanx jhance. But what do you mean with "Another possibility is one of the NT add-ons that run underneath NT and provide real-time services in an NT environment"?
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ID: 2604626
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