Read as54047d sensor from c on raspberry pi

as5047d.c

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

static uint8_t mode = 1;
static uint8_t bits = 8;
static uint32_t speed = 1000000;
static uint16_t delay = 0;

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

static void pabort(const char *s) {
  perror(s);
  abort();
}

static void transfer(int fd) {
  int i = 0;
  int ret;
  uint8_t tx[] = { 0xff, 0xff };
  float angle;

  uint8_t rx[ARRAY_SIZE(tx)] = {0, };
  struct spi_ioc_transfer tr = {
    .tx_buf = (unsigned long)tx,
    .rx_buf = (unsigned long)rx,
    .len = ARRAY_SIZE(tx),
    .delay_usecs = delay,
    .speed_hz = speed,
    .bits_per_word = 0,
  };

  while (1 == 1) {
    ret = ioctl(fd, SPI_IOC_MESSAGE(1), &tr);
    angle = (((rx[0] << 8) | rx[1]) & 0B0011111111111111);
    printf("%0.2f\n",  angle * 0.02197265625);
    //i++;
  }
}

int main(int argc, char **argv)
{
  char *name;
  int fd;
  struct spi_ioc_transfer xfer[2];
  unsigned char buf[32], *bp;
  int len, status;
  int ret = 0;


  name = argv[1];
  fd = open(name, O_RDWR);
  if (fd < 0) {
    perror("open");
    return 1;
  }

  // spi mode
  ret = ioctl(fd, SPI_IOC_WR_MODE, &mode);
  if (ret == -1 )
    pabort("can't set spi mode");

  ret = ioctl(fd, SPI_IOC_RD_MODE, &mode);
  if (ret == -1)
    pabort("can't get spi mode");

  /*
  * bits per word
  */
  ret = ioctl(fd, SPI_IOC_WR_BITS_PER_WORD, &bits);
  if (ret == -1)
    pabort("can't set bits per word");

  ret = ioctl(fd, SPI_IOC_RD_BITS_PER_WORD, &bits);
  if (ret == -1)
    pabort("can't get bits per word");

  /*
  * max speed hz
  */
  ret = ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed);
  if (ret == -1)
    pabort("can't set max speed hz");

  ret = ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed);
  if (ret == -1)
    pabort("can't get max speed hz");

  printf("spi mode: %d\n", mode);
  printf("bits per word: %d\n", bits);
  printf("max speed: %d Hz (%d KHz)\n", speed, speed/1000);

  transfer(fd);
  close(fd);

  return ret;
}