RE: [avr-libc-dev] [bug #22878] eeprom_*_word/dword/block cause hangin ATmega256x

[Stu Bell]

"Is avr-gcc for avr6 ready to use?"  Yes, with warnings.  Since gcc
insists on the size of a function pointer to be 2 bytes, anything using
function pointers must be used with caution.  If the function resides in
the lower half of flash, the 2 byte pointer works fine.

The problem is when the function resides in upper memory.  Then, the 2
byte pointer will point to the wrong place.

Note that normal function calls work fine.  Avr-gcc has been modified to
handle that case, through the use of the linker "trampoline" section.
It is just function pointers that give problems.

I've been using avr-gcc with the ATmega2560 for over 2 years now.
Although I'm picky about how my modules are linked (so the functions
that have pointers reside in low flash), the code is successful.

I will admit that I would not recommend the avr6 to people with little
experience in programming.

Best regards, 

Stu Bell 
DataPlay (DPHI, Inc.) 


-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf Of
Dmitry K.
Sent: Wednesday, April 09, 2008 12:24 AM
To: address@hidden
Subject: Re: [avr-libc-dev] [bug #22878] eeprom_*_word/dword/block cause
hangin ATmega256x

Hm...

Is avr-gcc for avr6 ready to use?

I have try avr-gcc 4.4-20080404 (4.3.0 does not support avr6) with
binutils 2.18.  In result the small program without any EEPROM usage and
without any inline functions gives incorrect
code:

/* avr-gcc 4.4-20080404 + binutils 2.18 produce incorrect code: the
foo4()
   function stores 0 value to 'vp' variable.
   Options: -W -Wall -Os -mmcu=atmega2560  */

#define BIGCODE()       asm volatile (".rept 30000\n\tnop\n\t.endr")

void (* volatile vp) (void);

__attribute__((noinline)) void foo1 (void)  { BIGCODE(); vp = foo1; }
__attribute__((noinline)) void foo2 (void)  { BIGCODE(); vp = foo2; }
__attribute__((noinline)) void foo3 (void)  { BIGCODE(); vp = foo3; }
__attribute__((noinline)) void foo4 (void)  { BIGCODE(); vp = foo4; }

int main ()
{
    foo1 ();
    foo2 ();
    foo3 ();
    foo4 ();
    return 0;
}


I will see the bug report later.

Dmitry.



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