Re: [avr-gcc-list] Large array in the FLASH size limitation

[David Sowa]

Alex Chernyshoff wrote:
> Hi!
>
> My attempts to declare array of chars in the FLASH
> memory
> is failure, if size of array more then 0x07fff.
> Probably, GCC use INT data type to calculate array
> size...
> I use "avrfreaks" windows build AVR-GCC 3.2 with the
> avr-libc-20020630,
> makefile is standart with "MCU = atmega103"
>
> Is it a bug, or exist some way to avoid this size
> limitation?

None of the AVR c compilers seem to have come to grips
with having an address space bigger than an int issue yet.

Not that I'm complaining, the AVR is a great little micro
but its 3 address space model does make it hard to map
into standard c.

I had this same issue on my project and here are the
workarounds I use.

For the arrays I need I wrote a utility that breaks the
data into 0x7000 byte chunks.  If these are declared one
after another in your code the compiler/linker will put
them continously into the flash and you can treat them
like one big array.

The next problem you may run into is that GCC can't give
a proper pointer to a flash array that begins after the
0x8000 point in flash, it always converts them to an int
for you.

I ended up needing to write my own flash memory routines
because the code generated by gcc uses the LPM instruction
and I needed the ELPM instruction to get at the data past
the 0x8000 point.

So basically I'm saying, force the compiler to build the
data into flash the way you want it, then get a pointer to
your big block of stuff and get at it that way.

Regards,
David Sowa

avr-gcc-list at http://avr1.org