Re: gcc-avr 4.9.2 -Os messes with interrupt vectors

God, thank you so much! I have had this issue for days without finding a 
solution! Using avr-gcc with mmcu=atmega168 instead of avr-ld with mavr5 
appears to have solved the problem!

As you suggested, I used -v to see what is going on and you are right, I was 
missing the correct CRT file!

Thank you so much, Senthil! You saved me a lot of time and headache!

8. Mai 2016 16:16 von [email protected]:


>
> [email protected]>  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 >> [email protected]>> :
>>
>>
>>> 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, "> >>> [email protected]>>> > " <> 
>>> >>> [email protected]>>> >
>>> > 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 > >>> [email protected]>>> > :
>>>
>>>
>>>> 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, ">> >>>> [email protected]>>>> >> 
>>>> " <>>
>>>> [email protected]>>>> >> > 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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>>>>
>>>>
>>>>   >>  >>
>>>
>>>
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