Re: [avr-chat] far addresses

[Bob Paddock]

Not sure if your issue is the related to this one?:

https://lists.nongnu.org/archive/html/avr-libc-dev/2010-09/msg00046.html

As Bob Paddock wrote:

> From the error that I'm getting, below, I belive that __data_load_end
> is only 16 bits wide?

No, obviously it's wider:

 0x0003c370   __data_load_start = LOADADDR (.data)
 0x0003c378   __data_load_end = (__data_load_start + SIZEOF (.data))

(That's from a map file.)

Note that the linker has no notion of what C knows as a "type".  It
only has symbols.

>   uint16_t flash_end_u16 = (uint16_t) &(__data_load_end[0]);

Your problem is that the & operator makes a pointer out of something
else, and pointers in AVR-GCC are fixed to 16 bits in size.  You have
to avoid turning the large integer __data_load_end actually is into a
pointer (syntactically).  I couldn't find any way using C syntax for
this, unless resorting straight to assembly:

static inline uint32_t get_data_load_end(void)
{
  uint32_t tmp;

  asm volatile("ldi %A0, lo8(__data_load_end)" "\n"
               "ldi %B0, hi8(__data_load_end)" "\n"
               "ldi %C0, hlo8(__data_load_end)" "\n"
               "ldi %D0, hhi8(__data_load_end)"
               : "=r"(tmp));
  return tmp;
}



On Fri, Aug 25, 2017 at 5:02 AM, Bob von Knobloch <address@hidden> wrote:
> Hi,
> I'm rewriting a project I originally had running on a ATMega 644.
> Now I need more space, so an ATMega 1284 is my choice.
> I need to have a very large amount of constant data in flash (more than fits
> under the 64k address range).
> My problem is that I must get the address of some constants in high (above
> 0x10000) memory and here the 'address of' a char[] does not return the right
> value.
>
> Example:
> I have string constant 'mystring' at address  0x11808 (can see it in the
> .map and .lst files). Using 'print_func(mystring);', which should print this
> address, albeit truncated to 16bits, returns '0x1e57'. I cannot see a
> connection here.
> Anyone tried to do similar things?
>
> Regards,
>
> Bob von Knobloch
> --
> The Sun is out, the sky is blue, it's time to drive the MR2.
>
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