I thought I read recently that there is a nicer way to declare and access flash-based data. Did I dream that, misunderstand, or is it true? Didn't find anything with some searches. Thanks.
kk6gm
Is there a replacement for PROGMEM and its access functions?
Author
Message
sternst
kk6gm wrote:
Search for "__flash".
Didn't find anything with some searches.
clawson 
Level: Moderator
Joined: Mon. Jul 18, 2005
Posts: 104937 View posts
Location: (using avr-gcc in) Finchingfield, Essex, England
kk6gm
Thanks, guys, this is SO much nicer! Anybody know when it was added?
david.prentice As a silly question.
Is there a mechanism for sensible handling of anonymous strings?
Or do you have to continue with the PSTR() abortion?
David.
SprinterSB
The problem with PSTR is that pointers to it will point to the generic space (RAM). PSTR locates in flash but that does not change the address space to flash.
If you use a consumer function that uses const __flash* then it will still read from flash and you get the desired behavior.
You can read the Embedded C extension ISO/IEC TR 18037 for the gory details. IMO there are some shortcomings regarding string literals. PSTR should cast the outgoing address to const __flash char* provided the built-in macro __FLASH is defined. PSTR only works locally whereas ((const __flash char[]) { "foo" }) will only work globally.
david.prentice The compiler can recognise a named literal or an anonymous literal.
CodeVision and ImageCraft handle it very well.
8051 compilers have always put anonymous strings in __code memory.
Yes, I agree that you do occasionally get anomalies. And after many years of wrapping strings with PSTR(), there is no great problem just continuing.
OTOH, I am sure that the whole subject could be handled more elegantly.
David.
gchapman
Level: 10k+ Postman
Joined: Tue. Jan 9, 2007
Posts: 16594 View posts
Location: Clay County, Texas, u.S.A.
kk6gm wrote:
Formally, 2012-Mar-22.Anybody know when it was added?
http://gcc.gnu.org/gcc-4.7/changes.html (search for named)
SprinterSB
Better: search for avr to find *all* relevant changes.
joeymorin
SprinterSB wrote:
I've used __flash locally:PSTR only works locally whereas ((const __flash char[]) { "foo" }) will only work globally.
void foo(void) {
static const __flash char bar[] = { "foobar" };
...
Or did you mean something else?
|
"Experience is what enables you to recognise a mistake the second time you make it." "Good judgement comes from experience. Experience comes from bad judgement." "Wisdom is always wont to arrive late, and to be a little approximate on first possession." "When you hear hoofbeats, think horses, not unicorns." "Fast. Cheap. Good. Pick two." "We see a lot of arses on handlebars around here." - [J Ekdahl] |
 |
SprinterSB
Consider code like that:
#define FSTR(X) ((const __flash char[]) { X })
const __flash char *pstr = FSTR ("foo");