Electronic Circuits and Projects Forum

Originally Posted by kubeek

I know I can hack in there pullups, but this is not very nice on already produced boards.

Not nice but very common.

Originally Posted by kubeek

Ok I found that the 0.5ms for the C init wasn´t the biggest problem, the default setting of 16K cycles + 65ms startup delay was much worse.
Still, is there a way in avr-gcc to do what I intended?

Yes:

Code :

#include <avr/io.h>
 
void my_init_portb(void) __attribute__ ((naked)) __attribute__ ((section (".init0")));
 
void my_init_portb(void)
{
        PORTB = 0xff;
        DDRB = 0xff;
}

http://nongnu.org/avr-libc/user-manu..._sections.html
The "naked" attribute strips off all the function entry and exit code. The section(".init0") defines the memory location where the piece of code is placed.