Re: [avr-chat] far addresses

[Bob von Knobloch]

On 25/08/17 16:31, Rolf Pfister wrote:
> Am 25.08.2017 um 15:27 schrieb Bob von Knobloch:
> > Well, the problem is that the compiler doesn't appear to return the correct 
> > address for constants (even when only the lower 16bits are examined) when 
> > accessing objects above 64k.
> > It must be capable internally, I have code running there.
>
> Code example, compiler version?
> If you think its a compiler bug, maybe it could be helpful to
> look at the created assembler code.
>
> Rolf
>
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Hi Rolf,

Compiler is:
avr-gcc (AVR_8_bit_GNU_Toolchain_3.5.0_1662) 4.9.2

code is like:

const char teststring[] PROGMEM = "some text";                // Loaded with a 
SECTION statement and a linker map at 0x01b000 (high memory) (and checked that it really 
is there)

hex32out(teststring);                                   // Prints the hex value 
of the address of teststring

result: 00007187                                        // No relation to the 
address

Anyway, Jörg Wünsch has commented somewhere that all such strings should be put 
into low memory, so I think this is an indication that the compiler cannot be 
used this way. I wouldn't call it a bug as the compiler is constructed for 
processors with a 16-bit address space. Just that AVR have extended it by using 
special instructions that we probably can't expect the compiler to support.
I have reorganised my code so that all symbolically addressed objects reside 
under 0x10000 and those above are numerically addressed (luckily I could do 
this, originally I had otherwise planned).

Anyway thanks for replying and maybe this helps someone.

Cheers,
Bob

--
The Sun is out, the sky is blue, it's time to drive the MR2.