void spi_wr(unsigned char d)
{
   SPDR = d;
   while ((SPSR & 0x80) == 0)
      ;
}

unsigned char spi_rd(void)
{
   unsigned char v;
   SPDR = 0xFF;
   while ((SPSR & 0x80) == 0)
      ;
   v    = SPDR;
   return (v)
}