Returning a value from an Interrupt?

RandyR

I'm trying to update a counter variable from within an interrupt, but the value is lost after returning from the interrupt code. I'm running the SX/B 2.00.21 beta.

I've tried using the INTERRUPT NOCODE command among other things to no avail. Any suggestions?

JonnyMac

Can you post your code? There is no reason for your value becoming "lost" -- I use interrupts to handle timers, etc. which means the values are not being lost.

RandyR

Thanks for the quick response!

Here's an abreviated version of the code. When the sensor is taken high, the interrupt is triggered and the IF statement within the interrupt turns on LED1. But the same IF statement below in the main program won't turn on LED2.

DEVICE SX28, OSC4MHZ, TURBO, STACKX, OPTIONX
FREQ 4_000_000

Sensor PIN RB.0 INPUT INTR_RISE
LED1 PIN RA.0 OUTPUT
LED2 PIN RA.1 OUTPUT
Counter VAR Byte

INTERRUPT NOCODE
ISR_Start:
· IF Sensor = 1 THEN
· · Counter = 60
· · IF Counter <> 0 THEN
· ··· LOW LED1
· ··· Pause 200
· ··· HIGH LED1
· · ENDIF
· ENDIF

ISR_Exit:
· WKPND_B = %00000000
RETURNINT

PROGRAM Start

Start:
· WKED_B = %11111000
· WKEN_B = %11111000
· WKPND_B = %00000000
· HIGH LED1
· HIGH LED2
· Counter = 0

Main:
· IF Counter <> 0 THEN
· · LOW LED2
··· Pause 200
··· HIGH LED2
· ENDIF
· PAUSE 5000
· Counter = 0
GOTO Main


Post Edited By Moderator (Bean (Hitt Consulting)) : 4/24/2009 1:21:39 PM GMT

JonnyMac

You're going to get strange behavior putting PAUSE in your interrupt, but that won't corrupt "counter." What are you trying to accomplish? I would suggest simply setting a flag in the interrupt and letting the foreground take care of blinking the LEDs for you.

RandyR

Agreed about the pause statements. I only have the LED's (and pauses) there to test the code. The full application has 3 sensors, 3 relays and 10 DIP switches and everything else works great. The code above is the test code I'm using to isolate and resolve this one problem. I've tried dozens of combinations and I simply can't get the interrupt code to pass a value back to the main program.

Can you suggest how I might set a flag? I'll try anything at this point...

Bean

Randy,
First of all remove the NOCODE option from the INTERRUPT line.

Second, I don't see anywhere in your code where you are changing the value of counter ? You test it at a couple places and assign it a value in a couple places but how are you expecting it's value to change ?

Bean.

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There is a fine line between arrogance and confidence. Make sure you don't cross it...

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RandyR

The "Counter = 60" statement within the interrupt code should change the value, shouldn't it? I removed the NOCODE option, but still same result.

Dave Hein

Randy,

Which variable are you having trouble with?· Is it Counter or WKPND_B?· Do the LEDs flash correctly when you get the interrupt?· If both LEDs flash, then the main routine is see the new value of Counter OK.· Is the value of KDPND_B the problem?

I don't understand the reason for the "IF Counter <> 0" statement.· The line above it set the value of Counter to 60, so it will alway be nonzero.

Dave

Bean

Randy,
Are you expecting the variable "Counter" to be automatically incremented with each interrupt ? It will not be. You will need a "INC Counter" in the interrupt routine to make that happen.

Bean.

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There is a fine line between arrogance and confidence. Make sure you don't cross it...

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RandyR

I'm having trouble with "Counter", but I think I have just found the issue!

The interrupt was occurring (and returning) into the pause which is followed by a reset of the counter variable! My error seems to be caused by confusion with the delays in the program execution. I'll work on correcting this in the full production code and confirm.

Thanks for all the prompt responses!!