Re: [avr-gcc-list] GCC Startupcode

[Andreas Strodl]

Hi,

Thanks, that seems to be what I need.
With that init function I could do some comunication with the connected
computer fast after reset leaving the startupcode itself untouched.
The main program itself may start a bit later.
Thanks to all.

Andreas Strodl


"Theodore A. Roth" wrote:
> 
> On Mon, 14 Jun 2004, Andreas Strodl wrote:
> 
> > Hi,
> >
> > I am working on a project where I need a ATmega16 to start up very fast
> > after a reset. Since after a reset the startupcode is always executed
> > first operation of the main programm starts to late. Now I am thinking
> > about modifying the startupcode. Could anyone please tell me were I can
> > find that startupcode in the AVRlibc and if there is somthing special
> > to care about.
> 
> The startup code already has facilities to do want you want so you
> shouldn't need to rewrite anything. All you need to do is write a naked
> function and insert it into the .init1 section.
> 
> Your function should be defined like this:
> 
> void myinit(void) __attribute__ ((naked)) __attribute__ ((section 
> (".init1")));
> void
> myinit(void)
> {
>   /* do early init stuff */
> }
> 
> Your init funciton should not have a RET asm insn in it.
> 
> If you need to use the stack for anything in your init code, you should
> use the .init3 section instead of the .init1 section.
> 
> Have a look at this in the "The .initN Sections" section:
> 
>   http://www.nongnu.org/avr-libc/user-manual/mem_sections.html
> 
> Alternatively, you could write a function named __init() and the reset
> vector will jump right into that, but then you would not get the other
> .initN sections executing.
> 
> It's very instructional to do a disassemble of your rom image and look
> through the startup code to see what is going on. You can do that with
> avr-objdump like this:
> 
>   $ avr-objdump -S rom-image.elf
> 
> ---
> Ted Roth
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