/****************************************
*    basic SPI demo for mcp23s17        *
*****************************************/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/spi/spidev.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

#include <stdint.h>

#define	CMD_WRITE	0x40
#define CMD_READ	0x41

static char       *spiDevice = "/dev/spidev0.0" ;
static uint8_t     spiMode   = 0 ;
static uint8_t     spiBPW    = 8 ;
static uint32_t    spiSpeed  = 5000000 ;
static uint16_t    spiDelay  = 0;

// MCP23S17 Registers

#define	IOCON		0x0A

#define	IODIRA		0x00
#define	IPOLA		0x02
#define	GPINTENA	0x04
#define	DEFVALA		0x06
#define	INTCONA		0x08
#define	GPPUA		0x0C
#define	INTFA		0x0E
#define	INTCAPA		0x10
#define	GPIOA		0x12
#define	OLATA		0x14

#define	IODIRB		0x01
#define	IPOLB		0x03
#define	GPINTENB	0x05
#define	DEFVALB		0x07
#define	INTCONB		0x09
#define	GPPUB		0x0D
#define	INTFB		0x0F
#define	INTCAPB		0x11
#define	GPIOB		0x13
#define	OLATB		0x15


int spi_fd;

static uint8_t readByte (uint8_t reg)
{
  uint8_t tx [4] ;
  uint8_t rx [4] ;
  struct spi_ioc_transfer spi ;

  tx [0] = CMD_READ ;
  tx [1] = reg ;
  tx [2] = 0 ;

  spi.tx_buf        = (unsigned long)tx ;
  spi.rx_buf        = (unsigned long)rx ;
  spi.len           = 3 ;
  spi.delay_usecs   = spiDelay ;
  spi.speed_hz      = spiSpeed ;
  spi.bits_per_word = spiBPW ;

  ioctl (spi_fd, SPI_IOC_MESSAGE(1), &spi) ;

  return rx [2] ;
}

static void writeByte (uint8_t reg, uint8_t data)
{
  uint8_t spiBufTx [3] ;
  uint8_t spiBufRx [3] ;
  struct spi_ioc_transfer spi ;

  spiBufTx [0] = CMD_WRITE ;
  spiBufTx [1] = reg ;
  spiBufTx [2] = data ;

  spi.tx_buf        = (unsigned long)spiBufTx ;
  spi.rx_buf        = (unsigned long)spiBufRx ;
  spi.len           = 3 ;
  spi.delay_usecs   = spiDelay ;
  spi.speed_hz      = spiSpeed ;
  spi.bits_per_word = spiBPW ;

  ioctl (spi_fd, SPI_IOC_MESSAGE(1), &spi) ;
}

/*spi_open
*      - Open the given SPI channel and configures it.
*      - there are normally two SPI devices on your PI:
*        /dev/spidev0.0: activates the CS0 pin during transfer
*        /dev/spidev0.1: activates the CS1 pin during transfer
*
*/
int spi_open(char* dev)
{
  if((spi_fd = open(dev, O_RDWR)) < 0){
    printf("error opening %s\n",dev);
    return -1;
  }
  return 0;
}

int main(int argc, char* argv[])
{
    unsigned char data = 0xAF;
    if(argc <= 1){
        printf("too few args, try %s /dev/spidev0.0\n",argv[0]);
        return -1;
    }
    // open and configure SPI channel. (/dev/spidev0.0 for example)
    if(spi_open(argv[1]) < 0){
        printf("spi_open failed\n");
        return -1;
    }

  writeByte (IODIRA, 0x00) ;	// Port A -> Outputs
  writeByte (GPIOA, 0xFF) ;
  //writeByte (IPOLB, 0x01) ; // invert lsb
  //writeByte (GPPUB, 0xFF) ; // enable pullups.
  writeByte (IODIRB, 0xFF) ;	// Port B -> Inputs
  data = readByte (GPIOB) ;

  printf("RECEIVED: %.2X\n",data);
  close(spi_fd);
  return 0;
}