[avr-gcc-list] Re: Larger than 64K memory sections

[David Brown]

Jan Waclawek wrote:
> > > I am using a 4MB flash memory with my Mega64. I would like to
> > > create a memory section for the entire 4MB. Is it possible? If
> > > yes, how can this be done in the makefile? Thank you very much
> > > for your time.
> > You can't directly access such large memory areas from an AVR,
> > therefore it makes no sense to talk about a memory section for it.
>
> IMHO your implication is incorrect. Even if there's no builtin
> support for non-RAM variables in avr-gcc (yet), we already have
> sections for EEPROM and FLASH - and the latter can be >64kB large.

Yes, that's true.  I hadn't thought about the EEPROM sections, mainly 
because I think they are often a bad idea in practice and thus don't use 
them (it's far too easy for the final addresses to change between 
builds, making a mess of stored data after changing the software.  I 
much prefer to use a struct at a fixed manually-specified address to 
order my eeprom data).

Still, without direct access the OP will need manual paging at least 
(and possibly more manual work - for all we know, this could be a serial 
flash, or 16-bit flash connected via GPIOs, or whatever).

Memory sections and pointer arithmetic get messy or impossible after 32K 
or 64K limits.  A 4MB section may also crash with other sections in the 
linker file unless you are very careful.

All in all, I can't see any advantage to the OP in using memory sections 
here, and I can see a great many complications if it can be made to work 
at all.