spi.c

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

#include "spi.h"

// Reference:
//   https://www.kernel.org/doc/Documentation/spi/
//   https://www.kernel.org/doc/Documentation/spi/spi-summary
//   https://www.kernel.org/doc/Documentation/spi/spidev


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

#define SPI_MSB_FIRST       0
#define SPI_BITS_PER_WORD_8 8
#define SPI_BITS_PER_WORD_9 9
#define SPI_SPEED_500KHZ    500 * 1000 // Raspberry Pi minimum
#define SPI_SPEED_6MHZ      6 * 1000 * 1000 // Rerported LCD Maximum
#define SPI_SPEED_3815HZ    3815 // Linux minimum
#define SPI_DELAY_0         0
#define SPI_DELAY_MIN       2980 // Minimum tested value
#define SPI_CS_CHANGE       1 // Don't clear CS between messages
                              // Actually should be cleared according
                              // to the epson data sheets

const uint32_t DELAY     = SPI_DELAY_0;
const uint32_t SPEED     = SPI_SPEED_6MHZ;
const uint32_t BPW       = SPI_BITS_PER_WORD_9;
const uint32_t CS_CHANGE = SPI_CS_CHANGE;

int spi_init(const char* dev) {
  uint8_t  mode      = SPI_CPOL; // => SPI_CPOL (per the EPSON data sheet)
                                 //    not SPI_CPHA
  uint8_t  lsb_first = SPI_MSB_FIRST;
  uint8_t  bpw       = BPW;
  uint32_t speed     = SPEED;

  int fd = open(dev, O_RDWR);

  if (fd < 0)
    return fd;

  if (ioctl(fd, SPI_IOC_WR_MODE         , &mode     ) < 0) return -1;
  if (ioctl(fd, SPI_IOC_WR_LSB_FIRST    , &lsb_first) < 0) return -1;
  if (ioctl(fd, SPI_IOC_WR_BITS_PER_WORD, &bpw      ) < 0) return -1;
  if (ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ , &speed    ) < 0) return -1;

  // printf("initializing device: %s\n"  , dev);
  // printf("spi mode: %d\n"             , mode);
  // printf("*lsb first: %d\n"           , lsb_first);
  // printf("bits per word: %d\n"        , bpw);
  // printf("max speed: %d Hz (%d KHz)\n", speed, speed/1000);

  return fd;
} 

int spi_send_word(int fd, uint16_t word) {
  struct spi_ioc_transfer tr = {
    .tx_buf        = (unsigned long) &word,
    .rx_buf        = (unsigned long) 0,
    .len           = 2,
    .delay_usecs   = DELAY,
    .speed_hz      = SPEED,
    .bits_per_word = BPW,
    .cs_change     = 0,
  };

  if (ioctl(fd, SPI_IOC_MESSAGE(1), &tr) < 0) {
    return -1;
  }

  return 0;
}

int spi_send_buffer(int fd, uint32_t len, void* data) {
  struct spi_ioc_transfer tr = {
    .tx_buf        = (unsigned long) data,
    .rx_buf        = (unsigned long) 0,
    .len           = 2 * len,
    .delay_usecs   = DELAY,
    .speed_hz      = SPEED,
    .bits_per_word = BPW,
    .cs_change     = 0,
  };

  if (ioctl(fd, SPI_IOC_MESSAGE(1), &tr) < 0) {
    return -1;
  }

  return 0;
}