mcp3008.c

#include <stdint.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/types.h>
#include <linux/spi/spidev.h>

#define ARRAY_SIZE(array) sizeof(array) / sizeof(array[0])

static const char *DEVICE = "/dev/spidev1.0";
static uint8_t MODE = SPI_MODE_0;
static uint8_t BITS = 8;
static uint32_t CLOCK = 1000000;
static uint16_t DELAY = 5;

/*
 * Ensure all settings are correct for the ADC
 */
static int prepare(int fd) {

  if (ioctl(fd, SPI_IOC_WR_MODE, &MODE) == -1) {
    perror("Can't set MODE");
    return -1;
  }

  if (ioctl(fd, SPI_IOC_WR_BITS_PER_WORD, &BITS) == -1) {
    perror("Can't set number of BITS");
    return -1;
  }

  if (ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &CLOCK) == -1) {
    perror("Can't set write CLOCK");
    return -1;
  }

  if (ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &CLOCK) == -1) {
    perror("Can't set read CLOCK");
    return -1;
  }

  return 0;
}

/*
 * (SGL/DIF = 0, D2=D1=D0=0)
 */ 
uint8_t control_bits_differential(uint8_t channel) {
  return (channel & 7) << 4;
}

/*
 * (SGL/DIF = 1, D2=D1=D0=0)
 */ 
uint8_t control_bits(uint8_t channel) {
  return 0x8 | control_bits_differential(channel);
}

/*
 * Given a prep'd descriptor, and an ADC channel, fetch the
 * raw ADC value for the given channel.
 */
int readadc(int fd, uint8_t channel) {
  uint8_t tx[] = {1, control_bits(channel), 0};
  uint8_t rx[3];

  struct spi_ioc_transfer tr = {
    .tx_buf = (unsigned long)tx,
    .rx_buf = (unsigned long)rx,
    .len = ARRAY_SIZE(tx),
    .delay_usecs = DELAY,
    .speed_hz = CLOCK,
    .bits_per_word = BITS,
  };

  if (ioctl(fd, SPI_IOC_MESSAGE(1), &tr) == 1) {
    perror("IO Error");
    abort();
  }

  return ((rx[1] << 8) & 0x300) | (rx[2] & 0xFF);
}


int main(int argc, char **argv) {

  int fd = open(DEVICE, O_RDWR);
  if (fd <= 0) {
    printf("Device %s not found\n", DEVICE);
    return -1;
  }

  if (prepare(fd) == -1) {
    return -1;
  }

  uint8_t i;
  for(i = 0;i < 8;i++) { 
    printf("Channel %d: %d\n", i + 1, readadc(fd, i));
  }

  close(fd);

  return 0;
}