On 31.01.2018 21:15, Paul "LeoNerd" Evans wrote:
On Wed, 31 Jan 2018 21:04:55 +0100
Joerg Wunsch <j...@uriah.heep.sax.de> wrote:
As Paul "LeoNerd" Evans wrote:
Does anyone have a suggestion on how I can have a string pointer to
a flash-stored string in a static initialiser?
This only works by allocating each of the string into a variable
(well, constant actually) in flash by itself, and then mention their
names in the struct initializer.
Hrm; that's upsettingly annoying. Is there perhaps a way this can be
convinced into working? I generally dislike the untidiness of having to
define lots of things above the main array definition, just so I can
pull them in by name into it, and use that name nowhere else. Inline
things would be nicer there.
If that static is not function-static, then __flash can be used:
#if !defined __FLASH || (defined __AVR_PM_BASE_ADDRESS__)
// For devices that see flash in RAM address space, resort to vanilla C.
#define __flash // empty
#endif // have __flash
#define FSTR(X) ((const __flash char[]) { X } )
const __flash char* const __flash animals[] =
{
FSTR ("mite"), FSTR ("slug"), FSTR ("sloth")
};
const __flash char flash[] = "flash";
const __flash char *pram_to_flash = FSTR ("pet");
const __flash char * const __flash pflash_to_flash = FSTR ("cat");
const __flash char* ani (int i)
{
return animals[i];
}
Notice that in contrast to progmem, __flash is a qualifier and *not* an
attribute. In particular, it matters where it occurs in a declaration,
e.g. whether left or right of a "*". gcc will generate accesses as
desired, no need for pgm_read macros or inline asm. However gcc rejects
FSTR for function-static so that there is no one-fits-all solution:
const __flash char* get_pet (void)
{
static const __flash char *pet = FSTR ("pet");
return pet;
}
In function 'get_pet':
error: compound literal qualified by address-space qualifier
return FSTR ("pet");
^~~~~~
Johann
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