wiringPiSPI.c

4 digit 7 segment 에 shift register를 연결해서 SPI 통신을 이용해 제어하고

RTC 모듈을 I2C 통신을 이용해 값을 가져오되

라이브러리를 사용하지 않고 만들기...

어쨌든 기존에 있는 라이브러리를 참고하고 필요한 함수만 떼어오는 것이 될 수 있으나

이 시도에 의미를 가지기로 한다

 

 

int wiringPiSPIDataRW (int channel, unsigned char *data, int len)
{
  struct spi_ioc_transfer spi ;

  channel &= 1 ;

// Mentioned in spidev.h but not used in the original kernel documentation
//	test program )-:

  memset (&spi, 0, sizeof (spi)) ;

  spi.tx_buf        = (unsigned long)data ;
  spi.rx_buf        = (unsigned long)data ;
  spi.len           = len ;
  spi.delay_usecs   = spiDelay ;
  spi.speed_hz      = spiSpeeds [channel] ;
  spi.bits_per_word = spiBPW ;

  return ioctl (spiFds [channel], SPI_IOC_MESSAGE(1), &spi) ;
}

spi_ioc_transfer > spidev.h

 

/**
 * struct spi_ioc_transfer - describes a single SPI transfer
 * @tx_buf: Holds pointer to userspace buffer with transmit data, or null.
 *	If no data is provided, zeroes are shifted out.
 * @rx_buf: Holds pointer to userspace buffer for receive data, or null.
 * @len: Length of tx and rx buffers, in bytes.
 * @speed_hz: Temporary override of the device's bitrate.
 * @bits_per_word: Temporary override of the device's wordsize.
 * @delay_usecs: If nonzero, how long to delay after the last bit transfer
 *	before optionally deselecting the device before the next transfer.
 * @cs_change: True to deselect device before starting the next transfer.
 *
 * This structure is mapped directly to the kernel spi_transfer structure;
 * the fields have the same meanings, except of course that the pointers
 * are in a different address space (and may be of different sizes in some
 * cases, such as 32-bit i386 userspace over a 64-bit x86_64 kernel).
 * Zero-initialize the structure, including currently unused fields, to
 * accomodate potential future updates.
 *
 * SPI_IOC_MESSAGE gives userspace the equivalent of kernel spi_sync().
 * Pass it an array of related transfers, they'll execute together.
 * Each transfer may be half duplex (either direction) or full duplex.
 *
 *	struct spi_ioc_transfer mesg[4];
 *	...
 *	status = ioctl(fd, SPI_IOC_MESSAGE(4), mesg);
 *
 * So for example one transfer might send a nine bit command (right aligned
 * in a 16-bit word), the next could read a block of 8-bit data before
 * terminating that command by temporarily deselecting the chip; the next
 * could send a different nine bit command (re-selecting the chip), and the
 * last transfer might write some register values.
 */
struct spi_ioc_transfer {
	__u64		tx_buf;
	__u64		rx_buf;

	__u32		len;
	__u32		speed_hz;

	__u16		delay_usecs;
	__u8		bits_per_word;
	__u8		cs_change;
	__u32		pad;

	/* If the contents of 'struct spi_ioc_transfer' ever change
	 * incompatibly, then the ioctl number (currently 0) must change;
	 * ioctls with constant size fields get a bit more in the way of
	 * error checking than ones (like this) where that field varies.
	 *
	 * NOTE: struct layout is the same in 64bit and 32bit userspace.
	 */
};

내일 마저 추가...

 

 

 

https://sites.uclouvain.be/SystInfo/usr/include/linux/spi/spidev.h