Re: [rtl] interrupt driven vs. periodic real-time tasks

[yodaiken@chelm.cs.nmt.edu]

The major problem with the PC architectures in RT is the obsolete  8253/4
timer. This timer is slow to program (off chip) and a general pain in the
ass to use. One of the examples in the RTL distribution shows how to use
the RTC for generating interrupts and for some purposes this is better.
For devices that can generate their own timing interrupts, you are far
better off using that interface and passing data either to a rtl task
or directly to a linux process. Palo improves things somewhat by
using the 8253 in periodic mode and trusting that interrupts are 
caught soon after being enabled. This permits him to _not_ reprogram
the timer on each interrupt. The price paid is that all periodic
tasks must have a reasonable greatest common divisor in their 
periods.

I have some experimental code for allowing the standard scheduler to
choose either periodic or one-shot (the current default) but it needs
some work.

Is their much interest out there in a scheduler that can attach to 
other interrupts?


On Sat, Oct 03, 1998 at 04:11:12PM -0400, Kurt Rosenfeld wrote:
> Hello everyone.  I hope you are all enjoying the fall weekend.
> 
> I am confused about the difference between interrupt-driven and periodic 
> real-time tasks.  From what I have read, it seems that the periodic tasks are 
> basically being driven by interrupts generated by a hardware timer in machine.  
> Is this true?  If this is true, it seems like all of the real-time timing 
> performance/statistics would be the same for an interrupt-driven and a periodic 
> task.  Is this true?  For example, do we get exactly the same performance from a 
> 1000Hz make_periodic task and an RT handler that responds to an 1000Hz external 
> hardware clock?
> 
> The answers to these questions might also be the answers to Donald Gaffney's 
> recent questions.
> 
> -kurt 
> 
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-- 

---------------------------------
Victor Yodaiken
Department of Computer Science
New Mexico Institute of Mining and Technology
Socorro NM 87801
Homepage		http://www.cs.nmt.edu/~yodaiken
PowerPC Linux page	http://linuxppc.cs.nmt.edu
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