Re: [avr-gcc-list] Allocation sequence of eeprom variables

[David Brown]

On 21/08/2012 10:38, Juergen Harms wrote:
> On 08/20/2012 10:10 PM, David Brown wrote:
> > Almost certainly, there is something wrong in your code, or in the way
> > you have declared your external data - the "-Wuninitialized" flag should
> > not give false positives as you describe.  (It can give false positives,
> > when you know yourself that all code paths that use the data have
> > initialised the variables but the compiler is unable to prove this.)
>
> I got rid of most of the "-Wuninitialized" warnings by introducing
> intermediate typedefs - for instance, replacing
>
> extern    const double    sunrise_fact[] PROGMEM;
>     by
> typedef double PROGMEM        prog_double;
> extern    const prog_double    *sunrise_fact;
>
>
> One single warning remains that I did not manage to suppress:
>
> extern    const prog_int8_t max_module;
>
> What is wrong with that? max_module is defined in another module and is
> initialised to a very constant value. The warning message is given when
> VersionPanel.c is compiled
>
> VersionPanel.c: In function 'ShowCpuInfo':
> VersionPanel.c:71:26: warning: uninitialized variable 'max_module' put
> into program memory area [-Wuninitialized]
>
> and the reference to max_module in ShowCpuInfo is:
>
>      if ( x_value <= pgm_read_byte ( &max_module ) ) {
>
> Any suggestions how to avoid this last warning - would be great if I get
> back to a make listing without warnings.

The use of "prog_int8_t" and similar types is deprecated:

<http://www.nongnu.org/avr-libc/user-manual/group__avr__pgmspace.html#ga48c7cb011ea5f82f4b73df40e07dff46>

These types had "PROGMEM" attached the progmem attribute to the type, 
rather than the variable, and I believe that does not work any more (if 
it ever did).

I don't think you should be getting an "unintialised" warning for:

extern const int8_t maxModule PROGMEM;

On older versions of avr gcc, there were spurious warnings - but I 
believe these have been fixed now.

The workaround for the warnings is simply to omit the "PROGMEM" on the 
extern declarations - it doesn't do anything anyway.