mehrfach gebrauch der SPI Schnittstelle

void display_sprite(uint16_t page, uint16_t byte, uint8_t x, uint8_t y, uint8_t w, uint8_t h) {

  speed_inc();

  mem_init_read(page, byte, 12);

  display_cmd((uint8_t *)0xef90, 0);

  display_cmd((uint8_t *)0x0500, 0);

  display_cmd((uint8_t *)(0x0800 | x), 0);

  display_cmd((uint8_t *)(0x0900 | (x + w - 1)), 0);

  display_cmd((uint8_t *)(0x0a00 | y), 0);

  display_cmd((uint8_t *)(0x0b00 | (y + h - 1)), 0);

  SPDR = 0xff;

  loop_until_bit_is_set(SPSR, SPIF);

  RPO_D_RS &= ~_BV(PIN_D_RS);

  for (uint16_t i = 0; i < w * h; ++i) {

    loop_until_bit_is_set(SPSR, SPIF);

    SPDR = SPDR;

    loop_until_bit_is_set(SPSR, SPIF);

    SPDR = SPDR;

  }

  loop_until_bit_is_set(SPSR, SPIF);

  RPO_MEM_CS |= _BV(PIN_MEM_CS);

  RPO_D_CS |= _BV(PIN_D_CS);

  speed_dec();

}

void mem_init_read(uint16_t page, uint16_t byte, uint8_t offset) {

  RPO_MEM_CS &= ~_BV(PIN_MEM_CS);

  RPO_D_CS |= _BV(PIN_D_CS);

  if (offset <= 4) {

    offset = 4 - offset;

  } else {

    if (byte < offset - 4) {

      page = (page - 1) & MEM_LASTPAGE;

      byte = 264 - (offset - 4) + byte;

    } else {

      byte -= (offset - 4);

    }

    offset = 0;

  }  

  SPDR = MEM_OP_CONTREAD;

  loop_until_bit_is_set(SPSR, SPIF);

  SPDR = H8(page << 1);

  loop_until_bit_is_set(SPSR, SPIF);

  SPDR = L8(page) << 1 | H8(byte);

  loop_until_bit_is_set(SPSR, SPIF);

  SPDR = L8(byte);

  loop_until_bit_is_set(SPSR, SPIF);

  for (; offset; --offset) {

    SPDR = 0xff;

    loop_until_bit_is_set(SPSR, SPIF);

  }

}