bug with timer0 interrupt?

Jonathan Geisler <[email protected]> Thu, 14 Feb 2013 10:06:06 -0500

Newsgroups	gmane.comp.hardware.avr.gcc
Message-ID	<[email protected]>

I'm encountering a strange error with avr-gcc 4.6.3 and 4.7.2 using
the timer interrupt.  The code I'm using is attached.  As you can see,
I was trying to tie in to the Arduino environment (with Eclipse) so
that I could help my students wean off that set of functions to being
able to use the hardware directly.

When I set up the library, I encountered a strange error and was able
to trace it back to this simple program that sets up the timer with a
prescalar of 1024 and then increments an unsigned long counter when
that timer overflows.  When the counter reaches a specific value, I
toggle the built-in LED on the Arduino board connected to PORTB.

The strange behavior is that if I initialize the counter to 0, the
code doesn't work--appearing to hang.  If I initialize the counter to
1, everything works perfectly.  I have verified that if I make a
similar change to the Arduino libraries that the original code begins
to work properly.

I'm not sure what the exact error is since I can use the Arduino
environment on my machine without a problem, but when I try to compile
it through Eclipse it gives me this error.  I'll include the build log
as an attachment in case particular compiler/linker flags are triggering
the error.

						-- Jonathan Geisler --

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main.cpp (text/x-c, 741 B)

/*
 * main.cpp
 *
 *  Created on: Feb 8, 2013
 *      Author: Jonathan Geisler
 */

//#define JGG

#ifdef JGG
#include "Arduino.h"
#else
#include <avr/interrupt.h>
#endif

void setup() {
#ifdef JGG
	pinMode(13, OUTPUT);
#else
	TCCR0A = 0;
	TCCR0B = 5;
	TIMSK0 = 1;
	sei();

	DDRB |= 0x20;
#endif
}

volatile unsigned long count = 1;  // bad executable if initialized to 0!!!

void loop() {
#ifdef JGG
	digitalWrite(13, HIGH);
	delay(1000);
	digitalWrite(13, LOW);
	delay(1000);
#else
	if (count > 50) {
		PORTB ^= 0x20;
		count = 0;
	}
#endif
}

#ifndef JGG
ISR(TIMER0_OVF_vect) {
	++count;
}

void init() {
	/* do nothing */
}
#endif

int main() {
	init();

#ifdef USBCON
	USBDevice.attach();
#endif

	setup();

	while (1) {
		loop();
	}
}

build.log (text/plain, 968 B)

make all 
Building file: ../main.cpp
Invoking: AVR C++ Compiler
avr-g++ -I"/home/jgeisler/src/eclipse/Arduino_Core/src" -DARDUINO=103 -Wall -Os -ffunction-sections -fdata-sections -fno-exceptions -mmcu=atmega328p -DF_CPU=16000000UL -MMD -MP -MF"main.d" -MT"main.d" -c -o "main.o" "../main.cpp"
Finished building: ../main.cpp
 
Building target: Arduino-on-Eclipse-1.elf
Invoking: AVR C++ Linker
avr-gcc -Wl,-Map,Arduino-on-Eclipse-1.map,--cref -Wl,--gc-sections -Os -L"/home/jgeisler/src/eclipse/Arduino_Core/328P_16MHz" -mmcu=atmega328p -o "Arduino-on-Eclipse-1.elf"  ./main.o   -lArduino_Core -lm
Finished building target: Arduino-on-Eclipse-1.elf
 
Invoking: AVR Create Extended Listing
avr-objdump -h -S Arduino-on-Eclipse-1.elf  >"Arduino-on-Eclipse-1.lss"
Finished building: Arduino-on-Eclipse-1.lss
 
Create Flash image (ihex format)
avr-objcopy -R .eeprom -O ihex Arduino-on-Eclipse-1.elf  "Arduino-on-Eclipse-1.hex"
Finished building: Arduino-on-Eclipse-1.hex

signature.asc (application/pgp-signature, 490 B)

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