Re: [avr-gcc-list] Fixed, external function "pointers"

[Erik Walthinsen]

Erik Christiansen wrote:
> The easiest way to do this is in the linker script. e.g. taking Dave's
> as a basis, modify
>
>   .data    : AT (ADDR (.text) + SIZEOF (.text))
>
> to
>
>   .data  0x800068  : AT (ADDR (.text) + SIZEOF (.text))
>
> and you've moved the vma up 8 bytes. (check with objdump -h)
Yeah, I'm probably going to have to write a linker script to simplify 
the compilation of application code.  Right now I add this to the cmdline:

        -Wl,-Tdata=0x800180 \
        -Wl,--section-start=.appsig=0x17fc \
        -Wl,--just-symbols=bootloader \

I'm completely unfamiliar with linker scripts, can I have a short linker 
script that contains *just* the above information and tacks onto / 
replaces the normal parameters just by listing it on the linker cmdline? 
 Or do I have to snapshot the entire linker script from a given version 
of ld and modify it slightly (and keep it up to date etc)?

> There's no compile-time data that needs to go into those 8 bytes, is
> there?
Nope, initialized by the bootloader code.  One of the big reasons for 
switching to pure ASM was to eliminate the rather significant chunk of 
code dedicated to just copying stuff around, even if it was never 
initialized in the C...

Speaking of redundancy, I haven't been able to find any documentation on 
the register-level ABI that avr-gcc expects, and thus what registers I 
do and don't need to save when writing my own ASM functions.  I see 
conflicting info in the compiler output, with the interrupt handlers 
saving almost all of the upper 16 even if they aren't all used, and 
others apparently not even saving registers they clobber (esp r30:r31).

Where can I find that info?

TIA,
   Omega
   aka Erik Walthinsen
   address@hidden