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Application of polling concept in Real Time Embedded Systems

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avssunil

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Polling Concept.

Hi,
I have a doudt in the polling concept.The processor polls for every N seconds to see if the device is ready and if so,the device finishes its job before X sec,what will happen in the N-X seconds???How will this latency be overcome in Real Time Embedded Systems???

Thanks.
Sunil
 

yasser_shoukry

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Polling Concept.

Polling is usually used with soft real time constraints, as the idle tasks(which contains polling) are usually assigned a low priority otherwise it will block other tasks from working.
 

avssunil

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Re: Polling Concept.

Hi,
Thanks for the asnwer,but what about hard real time systems????Will the interrupt concept come instead of polling,pls clear this also.
 

yasser_shoukry

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Polling Concept.

External Interrupts are used with asynchronous events, if you want to meet a hard real time periodic constraint then you have to rely on a timer interrupt, i.e. to program a timer (sometimes called alert) to schedule the task which implements this periodic hard real time constraint, of course this task should have a high priority so it will suspend any other task working on the kernel now.

Best Wishes
 

vsomeshwar

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Polling Concept.

This is very rare .
Usuallly processor always faster than IO devices.
 

yasser_shoukry

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Re: Polling Concept.

vsomeshwar said:
This is very rare .
Usuallly processor always faster than IO devices.

Of course a processor is faster than IO devices, but what i am talking about is when there are multiple tasks on the same kernel, then polling (idle) tasks should be given a low priority which can cause this task to be delayed , so it is not preferred to use polling with hard real time constraints
 

avssunil

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Re: Polling Concept.

Hi,
Thanks for the asnwer,but what about hard real time systems????Will the interrupt concept come instead of polling,pls clear this also.
 

jenardo

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Re: Polling Concept.

Hi,
If what you seek is polling an external device, then external interrupts will be used instead.
Else if you are seeking a periodical check on anything, then use timer interrupts.
 

cfant

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Re: Polling Concept.

Short answer to your question would be: depends. If your device require attention before x time, than you will have a problem. Other way to avoid this problem is to introduce buffer so that information can be stored until polling routine gets control.
 

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