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 | | From: | Mayank Kaushik | | Subject: | AT91RM9200: PIO: im getting two interrupts when i press the switch once :-( | | Date: | 10 Jan 2005 04:38:18 -0800 |
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 | Hi,
im learning how to use the AT91RM9200..right now im trying to tackle
the AIC. iv set everyhting up, earmarking PIOA0 for an external
interrupt through a switch connected to it, so that theoretically
whenever the switch is pressed, an interrupt is generated that sends a
string via the debug port to hyperterminal.
everythings fine, but when i press the switch once, i get 2
interrupts...one whenthe switch is down, the other when i release
it..ive tried this in all modes, level sensitive, edge sensitive, high
level, positive edge, etc, all possible ones..
i dont suppose its due to a contact bounce, since im getting symmetric
interrupts like this..im using the exact libraries provided by atmel
(irq_pio.s and irq.mac)..
kindly advise what could be going wrong..
Thanx in anticipation
Mayank
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| | From: | Tauno Voipio | | Subject: | Re: AT91RM9200: PIO: im getting two interrupts when i press the switch | | Date: | Tue, 11 Jan 2005 09:41:49 GMT |
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| Mayank Kaushik wrote:
> Hi,
>
> im learning how to use the AT91RM9200..right now im trying to tackle
> the AIC. iv set everyhting up, earmarking PIOA0 for an external
> interrupt through a switch connected to it, so that theoretically
> whenever the switch is pressed, an interrupt is generated that sends a
> string via the debug port to hyperterminal.
>
> everythings fine, but when i press the switch once, i get 2
> interrupts...one whenthe switch is down, the other when i release
> it..ive tried this in all modes, level sensitive, edge sensitive, high
> level, positive edge, etc, all possible ones..
> i dont suppose its due to a contact bounce, since im getting symmetric
> interrupts like this..im using the exact libraries provided by atmel
> (irq_pio.s and irq.mac)..
>
The culprit may be the mechanical switch. It sends numerous
contact/no contact cycles when the contacts are just
touching. This is called contact bounce. Have a look
at the voltage on the live switch contact with an
oscilloscope.
The classical method is to use a switch with both a
normally open and a normally closed contact. The contacts
are used to set and reset a simple flip-flop which changes
state at the first touch of a bounce and ignores the rest
of the bounces.
Another method is to force your program to ignore
the bounces with a timer.
It is not a good idea to feed an unprocessed switch
contact to an interrupt input.
HTH
--
Tauno Voipio
tauno voipio (at) iki fi
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| | From: | Mayank Kaushik | | Subject: | Re: AT91RM9200: PIO: im getting two interrupts when i press the switch once :-( | | Date: | 11 Jan 2005 01:56:56 -0800 |
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| it wasnt the contact..the pio in this controller can only trigger on
input changes, nothing else..soree for the bother :-s
but thanx for the debounce info, might come in handy later
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