10 Replies Latest reply on Oct 18, 2014 1:50 PM by user_14586677

A problem with ISRs

mahmoud.athab Aug 18, 2017 2:03 PM

Hi, I am building a simple digital piano for my little sister. Nothing serious, just some bush buttons connected to intterupts, when a button is pressed the intterupt writes a value to a control register. the control register works as a select signal for a mux. the mux inputs are differnet clocks which serve as the piano tunes.

Now, the hardware is connected perfectly, every intterupt triggers perfectly, so here is the weird part:

When I press the first bush button, which is the tune A, everything works as it should, the intterupt triggers, the control register is written, then the return statement is excuted which brings the program back to main.

when I press the second bush button, the intterupt triggers, the control register is written, but the return statment is IGNORED. the program just keeps going to the next ISR where the its return statment is also ignored, and the next and the next until it creats an infinte loop outside of main.

I have uploded the project on two links if you care to shed some light on this problem.

http://www.mediafire.com/download/sp7z1hvm2ccu3eh/Simple_Piano_Using_Square_Waves.Bundle01.zip

https://drive.google.com/file/d/0BwvX4pp-M0KyNzlqY00yWUZzOGc/view?usp=sharing

1. Re: A problem with ISRs

user_78878863 Oct 15, 2014 5:11 PM (in response to mahmoud.athab)

What do you mean with "goes to the next ISR"? Is the same ISR called again?

How did you find about this? With the debugger? The reason might be that the interrupt trigger is level-based and not edge-based. Then it will be active as long as the button is pressed (and be executed when the interrupt-flag is cleared inside of the ISR)
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2. Re: A problem with ISRs

mahmoud.athab Oct 15, 2014 5:58 PM (in response to mahmoud.athab)

Yes I found that problem using the debugger, and what I mean by "goes to the next ISR" is that it finishes whatever I programmed the ISR to do and moves to perform the next ISR although it was not triggered. for example, when I press button 2 (tone C) the C ISR is performed. as soon as it is finished it moves directly to perform the D ISR without the intterupt being triggered, and then moves to the E ISR and so on until it returns to the C ISR and creates a loop.

all the intteurpts are rising edge based.
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3. Re: A problem with ISRs

mahmoud.athab Oct 15, 2014 7:30 PM (in response to mahmoud.athab)

No need, I found the problem, it was with the switch connections.
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4. Re: A problem with ISRs

user_78878863 Oct 16, 2014 3:37 AM (in response to mahmoud.athab)

That sounds interesting. How does a faulty switch wiring cause triggering one ISR after another?
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5. Re: A problem with ISRs

user_14586677 Oct 16, 2014 6:19 AM (in response to mahmoud.athab)

GPIO Interrupts covered here (explanation of port wide behaviour) -





          http://www.cypress.com/?rID=57571



Regards, Dana.
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6. Re: A problem with ISRs

mahmoud.athab Oct 16, 2014 3:18 PM (in response to mahmoud.athab)

@hli, no idea. I connected 5 switches with a pull down resistor, but only the first switch worked as it should. I removed the pull down connections and it worked like a charm. it still is a very strange problem.

@Dana, the answer might be in your document, I'll make sure to read it.
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7. Re: A problem with ISRs

mahmoud.athab Oct 16, 2014 3:49 PM (in response to mahmoud.athab)

In the document provieded by Dana, on page 16 it mentions 2 ports configured as a rising edge and falling edge interrupts.

3. Configure P6[0] as a resistive pull-down pin, or add

an external pull-down.

4. Configure P6[1] as a resistive pull-up pin, or add an

external pull-up.



    it says "or add", but what if we do both. because I configured my ports as resistive pull down and added an external pull down at the same time. could that be what caused the problem?
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8. Re: A problem with ISRs

user_14586677 Oct 16, 2014 6:06 PM (in response to mahmoud.athab)

If you double up on PU's or PD's for sure you will burn more

power when switch closed.



Rare but if SW had high R when closed you might not meet noise margin,

eg. reflect a switch closure.



Just use internal, simpler.



Regards, Dana.
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9. Re: A problem with ISRs

mahmoud.athab Oct 18, 2014 1:37 AM (in response to mahmoud.athab)

Well, trust me Dana when I tell you that the lesson is well learned and won't be forgotten. Thank u.
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10. Re: A problem with ISRs

user_14586677 Oct 18, 2014 1:50 PM (in response to mahmoud.athab)

Glad the forum was able to help.

Regards, Dana.
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