Re: [avr-gcc-list] gcc-avr 4.9.2 -Os messes with interrupt vectors

[Senthil Kumar Selvaraj]

address@hidden writes:

> No, I will try to explain where my problem is. The code I posted before 
> should turn the LED connected to PB5 on. The code also contains an ISR, but 
> it is empty and as I never enable interrupts, it should never be called.

I guess you're not linking in the crt file for the device. The crt file
has startup code and the correct vector table for the device. Without
it, and without an alternate startup/vector table init code, you will
miss things like global variable initialization, SP setup etc., and
interrupt handlers won't run. 

Instead of
>>> avr-ld -mavr5 -o led-test.elf main.o

Can you invoke the compiler driver with the correct device i.e.?

avr-gcc -mmcu=atmega168 -o led-test.elf main.o

That way, the driver will invoke the linker with the correct crt object
file and other libraries. You can pass -v to see what exactly goes to
the linker.

Regards
Senthil

>
> The code works without optimizations, but with -Os enabled, the LED does 
> *not* turn on! If I remove the (empty) ISR and keep everything else the same, 
> the LED *does* turn on with optimizations enabled!
>
> My problem is not how to toggle the LED, I know how to do that. My problem is 
> that the code behaves differently when using the optimization option -Os.
>
> 8. Mai 2016 14:36 von address@hidden:
>
>
>> Hi,
>> "> I do *not* want the ISR to be called". I guess you do not want the 
>> interrupt to be enabled. If you do not start the timer (as the interrupt is 
>> timer related) this interrupt will never occur. If you are using the timer 
>> for something else and need the timer running, then you need not explicitly 
>> enable timer overflow interrupt (see TIMSK register bits). In the while 
>> loop, you are always setting the port bit which I guess is connected to the 
>> LED and the LED will glow when this bit is 1. Suggest toggling the LED 
>> through a while loop with delays (large enough to be able to see LED 
>> flashing) inserted.> > Regards,
>> Parthasaradhi
>> Hyderabad
>>
>>
>>  >  >  >  On Sunday, May 8, 2016 3:06 PM, "> address@hidden> " <> 
>> address@hidden> 
>> > wrote:
>>
>>
>>  > Thank you for your instant response.
>>
>> I am sorry if I was unclear about that: I do *not* want the ISR to be 
>> called. The LED should turn on because I enable it in main(), however, the 
>> uC goes straight to the ISR!
>>
>> For example, if I set the LED to high in the ISR and set it to low in 
>> main(), it will be set to high and the LED will turn on when I flash it. 
>> Even though I used cli()!
>>
>> This behavior appears to depend on -Os, so I guess I am either using the 
>> tools incorrectly, or there is a bug in the optimization code.
>>
>> 8. Mai 2016 11:22 von > address@hidden> :
>>
>>
>>> First off, you are disabling global interrupts (cli ()). You need to 
>>> enable them (sei ()). I presume you are toggling the LED in ISR, if so the 
>>> LED will not toggle as interrupts are disabled.>> >> Regards,
>>> Parthasaradhi
>>> Hyderabad
>>>
>>>
>>>  >>  >>  >>  On Sunday, May 8, 2016 2:40 PM, ">> address@hidden>> " <>> 
>>> address@hidden>> > wrote:
>>>
>>>
>>>  >>           >> Hello,
>>>
>>> I have been working on a project for some time and at some point, 
>>> everything just stopped working. It appears that as soon as I include an 
>>> ISR in my C code, the main function won't even be called anymore. I 
>>> reduced my code to this:
>>>
>>>
>>> #include <avr/io.h>
>>> #include <avr/interrupt.h>
>>>
>>> int main (void) {
>>>  cli();
>>>  DDRB = 0xff;
>>>  while(1) PORTB |= (1 << PB5);
>>>  return 0;
>>> }
>>>
>>> ISR(TIMER0_OVF_vect) {}
>>>
>>> But the LED just won't turn on. The strange thing is: If I remove the ISR 
>>> at the bottom without changing anything else, even keeping the include, 
>>> everything works. If I remove the -Os option from gcc but keep the ISR, 
>>> everything works.
>>>
>>> I use these commands to compile, link and flash it:
>>>
>>> F_CPU=16000000L
>>> avr-gcc -Wall -DF_CPU=$F_CPU -c -mmcu=atmega168 -Os main.c -o main.o
>>> avr-ld -mavr5 -o led-test.elf main.o
>>> avr-objcopy -O ihex led-test.elf led-test.hex
>>> sudo avrdude -c avrisp2 -p atmega168 -P usb -b 57600 -U 
>>> flash:w:led-test.hex
>>>
>>>
>>> I am quite new to the avr tools so I might just have made a silly mistake, 
>>> so I would appreciate any tips!
>>> Thank you!
>>>
>>>
>>> LSB:
>>> Distributor ID: Ubuntu
>>> Description: Ubuntu 16.04 LTS
>>> Release: 16.04
>>> Codename: xenial
>>>
>>> Output of avr-gcc -v:
>>> Using built-in specs.
>>> Reading specs from /usr/lib/gcc/avr/4.9.2/device-specs/specs-avr2
>>> COLLECT_GCC=avr-gcc
>>> COLLECT_LTO_WRAPPER=/usr/lib/gcc/avr/4.9.2/lto-wrapper
>>> Target: avr
>>> Configured with: ../src/configure -v --enable-languages=c,c++ 
>>> --prefix=/usr/lib --infodir=/usr/share/info --mandir=/usr/share/man 
>>> --bindir=/usr/bin --libexecdir=/usr/lib --libdir=/usr/lib --enable-shared 
>>> --with-system-zlib --enable-long-long --enable-nls 
>>> --without-included-gettext --disable-libssp --build=x86_64-linux-gnu 
>>> --host=x86_64-linux-gnu --target=avr CFLAGS='-g -O2 
>>> -fstack-protector-strong -Wformat ' CPPFLAGS=-D_FORTIFY_SOURCE=2 
>>> CXXFLAGS='-g -O2 -fstack-protector-strong -Wformat ' FCFLAGS='-g -O2 
>>> -fstack-protector-strong' FFLAGS='-g -O2 -fstack-protector-strong' 
>>> GCJFLAGS='-g -O2 -fstack-protector-strong' 
>>> LDFLAGS='-Wl,-Bsymbolic-functions -Wl,-z,relro' OBJCFLAGS='-g -O2 
>>> -fstack-protector-strong -Wformat ' OBJCXXFLAGS='-g -O2 
>>> -fstack-protector-strong -Wformat '
>>> Thread model: single
>>> gcc version 4.9.2 (GCC)
>>>
>>> _______________________________________________
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>>> https://lists.nongnu.org/mailman/listinfo/avr-gcc-list
>>>
>>>
>>>   >>  >>
>>
>>
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