Problem mit PORTA = 0xFF bei atmega32

#include <avr/io.h>

#include <avr/interrupt.h>

int steps[] = { 1,4,6,9,11,13,16,19,21,23,26,28,31,33,36,38,41,43,45,48,51,52,56,58,60,63,65,68,70,72,75,78,80,82,85,87,90,93,94,97,100,102,105,107,109,112,115,117,119,122,124,127,129,132,134,136,139,142,144,146,149,151,154,156,159,161,164,166,168,171,174,176,178,181,183,186,188,191,193,196,198,201,203,205,208,210,213,215,218,220,223,225,228,230,232,235,238,240,242,245,247,250,252,255,257,260,262,264,267,270,271,275,277,279,282,284,287,289,291,294,297,299,301,304,306,309,311,314,316,319,321,324,326,328,331,334,335,339,341,343,346,348,350,353,356,358,360,363,366,368,370,373,375,378,380,382,386,387,390,393,395,397,400,402,405,407,410,412,414,418,419,422,425,426,430,432,434,437,439,442,444,446,449,452,454,456,459,462,463,467,468,472,473,476,479,481,484,486,488,491,493,496,498,501,503,506,508,511,513,515,518,520,523,526,527,531,532,536,537,540,543,545,547,550,553,555,557,560,562,565,567,569,573,574,577,580,581,585,587,589,592,594,597,599,602,604,606,609,612,614,616,619,621,624,626 };

int cstep = 0;

int tep = 0;

char plus = 1;

int main (void) {

  DDRA  = 0xff;

  //TCCR1A = (1<<WGM11)|(1<<WGM10);

  //no prescaler and reset on compare on match

  TCCR1B = (1<<CS10)|(1<<WGM12);

  OCR1A = steps[cstep];

  TCNT1 = 0;

  //enable interrupt

  TIMSK = (1<<OCIE1A);

  sei();

  while(1) {

    if ( tep > 255 )

      plus = -1;

    else if ( tep < 0 )

      plus = 1;

    tep += plus;

    int i,j,k;

    for ( i = 0; i < 80; i++ )

      for ( j = 0; j < 100; j++ )i = i;

  }

   return 0;

}

ISR( TIMER1_COMPA_vect ){

  OCR1A = steps[++cstep];

  if ( cstep >= tep && PINA != 0 )

    PORTA = 0;

  //Schreib ich hier PORTA = 1; klappt es...

  if ( cstep == 1 )

    PORTA = 255;

  if ( cstep > 254 )

    cstep = 0;

  TCNT1 = 0;

  return;

}