Re: [avr-gcc-list] bug with timer0 interrupt?

[Jonathan Geisler]

On Fri, Feb 15, 2013 at 01:16:27AM +0100, Georg-Johann Lay wrote:
> Jonathan Geisler schrieb:
> > 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.
> 
> When you change count in the ISR and read it in main, the read must be 
> atomic.  Otherwise, you may see glitches and phantom values.
> 
> It atomic access does not help, you can compare the code generated with 
> your Eclipse setup and with your Arduino setup.

The atomic accesses didn't help.  I didn't include that originally
because the Arduino doesn't include them.

For my C code, they appear to be identical.  I didn't compare the
extra code added by the linker.

> You cal also check the generated assembly whether or not it is as you 
> expect.  If so, your problem is somewhere else.

The asm code for my C code appears to be correct.  That is what is so
perplexing to me.  Note that the test code is a distillation of what
the Arduino environment does and it quite succinct, but displays the
error quite reliably.

> You could also supply a test case that can be compiled and reproduced.
> 
> To get a test case, add -v -save-temps to the compiler options and 
> recompile.  Then post the console output of the compiler and the .ii file.

Here is the console output.  I'm attaching the .ii file and the .cpp
file used for the compilation.

    [227] jgeisler:~/classes/enp341 % avr-g++ -Wall -Os -ffunction-sections 
-fdata-sections -fno-exceptions -mmcu=atmega328p -DF_CPU=16000000UL -MMD -MP 
-MF"main.d" -MT"main.d" -c -o test.o test.cpp -v -save-temps
    Using built-in specs.
    COLLECT_GCC=/usr/x86_64-pc-linux-gnu/avr/gcc-bin/4.7.2/avr-g++
    Target: avr
    Configured with: 
/var/tmp/portage/cross-avr/gcc-4.7.2/work/gcc-4.7.2/configure --prefix=/usr 
--bindir=/usr/x86_64-pc-linux-gnu/avr/gcc-bin/4.7.2 
--includedir=/usr/lib/gcc/avr/4.7.2/include 
--datadir=/usr/share/gcc-data/avr/4.7.2 
--mandir=/usr/share/gcc-data/avr/4.7.2/man 
--infodir=/usr/share/gcc-data/avr/4.7.2/info 
--with-gxx-include-dir=/usr/lib/gcc/avr/4.7.2/include/g++-v4 
--host=x86_64-pc-linux-gnu --target=avr --build=x86_64-pc-linux-gnu 
--disable-altivec --disable-fixed-point --without-ppl --without-cloog 
--enable-lto --enable-nls --without-included-gettext --with-system-zlib 
--enable-obsolete --disable-werror --enable-secureplt --disable-multilib 
--disable-libmudflap --disable-libssp --disable-libgomp 
--with-python-dir=/share/gcc-data/avr/4.7.2/python 
--enable-poison-system-directories --enable-checking=release --disable-libgcj 
--disable-libquadmath --enable-languages=c,c++ --enable-shared 
--disable-threads --disable-bootstrap --with-bugurl=http://bugs.gentoo.org/ 
--with-pkgversion='Gentoo 4.7.2 p1.0, pie-0.5.3'
    Thread model: single
    gcc version 4.7.2 (Gentoo 4.7.2 p1.0, pie-0.5.3) 
    COLLECT_GCC_OPTIONS='-Wall' '-Os' '-ffunction-sections' '-fdata-sections' 
'-fno-exceptions' '-mmcu=atmega328p' '-D' 'F_CPU=16000000UL' '-MMD' '-MP' '-MF' 
'main.d' '-MT' 'main.d' '-c' '-o' 'test.o' '-v' '-save-temps'
     /usr/libexec/gcc/avr/4.7.2/cc1plus -E -quiet -v -MMD test.d -MF main.d -MP 
-MT main.d -D F_CPU=16000000UL test.cpp -mmcu=atmega328p -Wall 
-ffunction-sections -fdata-sections -fno-exceptions -Os -fpch-preprocess 
-fno-rtti -fno-enforce-eh-specs -fno-exceptions -o test.ii
    ignoring nonexistent directory "/usr/lib/gcc/avr/4.7.2/include/g++-v4"
    ignoring nonexistent directory "/usr/lib/gcc/avr/4.7.2/include/g++-v4/avr"
    ignoring nonexistent directory 
"/usr/lib/gcc/avr/4.7.2/include/g++-v4/backward"
    ignoring nonexistent directory 
"/usr/lib/gcc/avr/4.7.2/../../../../avr/sys-include"
    #include "..." search starts here:
    #include <...> search starts here:
     /usr/lib/gcc/avr/4.7.2/include
     /usr/lib/gcc/avr/4.7.2/include-fixed
     /usr/lib/gcc/avr/4.7.2/../../../../avr/include
    End of search list.
    COLLECT_GCC_OPTIONS='-Wall' '-Os' '-ffunction-sections' '-fdata-sections' 
'-fno-exceptions' '-mmcu=atmega328p' '-D' 'F_CPU=16000000UL' '-MMD' '-MP' '-MF' 
'main.d' '-MT' 'main.d' '-c' '-o' 'test.o' '-v' '-save-temps'
     /usr/libexec/gcc/avr/4.7.2/cc1plus -fpreprocessed test.ii -quiet -dumpbase 
test.cpp -mmcu=atmega328p -auxbase-strip test.o -Os -Wall -version 
-ffunction-sections -fdata-sections -fno-exceptions -fno-rtti 
-fno-enforce-eh-specs -fno-exceptions -o test.s
    GNU C++ (Gentoo 4.7.2 p1.0, pie-0.5.3) version 4.7.2 (avr)
            compiled by GNU C version 4.5.4, GMP version 5.0.2, MPFR version 
3.0.1-p4, MPC version 0.8.2
    warning: MPFR header version 3.0.1-p4 differs from library version 3.1.1.
    GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
    GNU C++ (Gentoo 4.7.2 p1.0, pie-0.5.3) version 4.7.2 (avr)
            compiled by GNU C version 4.5.4, GMP version 5.0.2, MPFR version 
3.0.1-p4, MPC version 0.8.2
    warning: MPFR header version 3.0.1-p4 differs from library version 3.1.1.
    GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
    Compiler executable checksum: 5e7b521416cf40df37e35c64e8937dd8
    COLLECT_GCC_OPTIONS='-Wall' '-Os' '-ffunction-sections' '-fdata-sections' 
'-fno-exceptions' '-mmcu=atmega328p' '-D' 'F_CPU=16000000UL' '-MMD' '-MP' '-MF' 
'main.d' '-MT' 'main.d' '-c' '-o' 'test.o' '-v' '-save-temps'
     /usr/libexec/gcc/avr/as -mmcu=atmega328p -mno-skip-bug -o test.o test.s
    
COMPILER_PATH=/usr/libexec/gcc/avr/4.7.2/:/usr/libexec/gcc/avr/4.7.2/:/usr/libexec/gcc/avr/:/usr/lib/gcc/avr/4.7.2/:/usr/lib/gcc/avr/
    
LIBRARY_PATH=/usr/lib/gcc/avr/4.7.2/:/usr/lib/gcc/avr/4.7.2/../../../../avr/lib/
    COLLECT_GCC_OPTIONS='-Wall' '-Os' '-ffunction-sections' '-fdata-sections' 
'-fno-exceptions' '-mmcu=atmega328p' '-D' 'F_CPU=16000000UL' '-MMD' '-MP' '-MF' 
'main.d' '-MT' 'main.d' '-c' '-o' 'test.o' '-v' '-save-temps'
    [228] jgeisler:~/classes/enp341 % 

                                                -- Jonathan Geisler --

test.cpp
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test.ii
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