Re: [avr-gcc-list] Startup code

[Dmitry]

>From your bootloader code you can jump to init procedure:


 void __attribute__ ((section(".bootloader"))) RunBootloader(void)
 {
 
   // My Bootcode
   asm volatile("jmp _real_init_"); // should be the last line.
 }


I am not sure if you need some frame space in your boot loader code. If you do 
not, it would be better if you  add __attribute__((naked)) to your 
RunBootloader(). 

If you need it - I am not sure if the hardware initializes a stack pointer or 
something. If it does not, you have to initialize it first and try something 
like:

 void __attribute__ ((section(".bootloader"))) __attribute__((naked)) 
RunBootloader(void)
 {
        // initialize frame pointer and stack pointer
        // stack pointer will be re-initialized in main
        asm volatile("
        ldi r28,lo8(__stack - %0)
        ldi r29,hi8(__stack - %0)
        out __SP_H__,r29
        out __SP_L__,r28 " 
                :: "i"((unsigned int)FRAME_SIZE_REQUIRED));     

        // now if you want to disable WDT
        asm volatile("
        ldi     r18, lo8(__init_wdtcr__)
        wdr
        out     %0, r18"
                :: "I"(WDTCR));
        
        // other registers likewise (see gcrt1.S in libc)...

        // your bootloader code

        asm volatile("jmp _real_init_"); // should be the last line.
}


hope it helps,
Dmitry.



On Wed, 30 Jan 2002 15:17:26 +0200
Pieter Potgieter <address@hidden> wrote:

> void __attribute__ ((section(".bootloader"))) RunBootloader(void)
> {
> 
>   // My Bootcode
> 
> }
> 
> Ok I got this far:
> The bootloader section is located at address 0x1FC00 by the linker.
> The fuse bit in the mega128 is set to jump to the bootloader address.
> 
> Question :
> Are there any startup code or registers that needs to be initialised in the 
> RunBootloader() procedure?  Because the normal startup code is only executed 
> when the mega starts executing from address 0x0000.
> 
> IOW what startup code is neccessary for the mega to start executing from an 
> address?
> 
> Regards
> Pieter Potgieter.
> 
> 
> 
> avr-gcc-list at http://avr1.org
> 


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