rem: for (i=0; i<4; i++) { avr_txrx ( fd, data[i] ); }
add: avr_cmd(fd, data, res);
context: int avr_chip_erase ( int fd ){  unsigned char data[4] = {0xac, 0x80, 0x00, 0x00};  int i;  for (i=0; i<4; i++) {    avr_txrx ( fd, data[i] );  }  usleep(20000);  return 0;}