利用内核自带的spi测试测试spi驱动的时候，mosi没有之恋miso，miso怎么也能收到数据？

#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>

#include <unistd.h>

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

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

static const char *device = "/dev/spidev2.0";
static uint8_t mode;
static uint8_t bits = 8;
static uint32_t speed = 1000; //500000;
static uint16_t delay;

static void transfer(int fd)
{
 int ret;
 
 //要发送的数据数组

 uint8_t tx[] = {
  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
  0x40, 0x00, 0x00, 0x00, 0x00, 0x95,
  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
  0xDE, 0xAD, 0xBE, 0xEF, 0xBA, 0xAD,
  0xF0, 0x0D,
 };

 

 

// uint8_t tx[] = {
//  0x55,0xaa,0xf5};
 
 uint8_t rx[ARRAY_SIZE(tx)] = {0, }; //接收的数据数据
 //声明并初始化spi_ioc_transfer结构体
 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 = bits,
 };

 //SPI_IOC_MESSAGE(1)的1表示spi_ioc_transfer的数量
 ret = ioctl(fd, SPI_IOC_MESSAGE(1), &tr);  //ioctl默认操作,传输数据
 if (ret == 1)
  pabort("can't send spi message");

 for (ret = 0; ret < ARRAY_SIZE(tx); ret++) { //打印接收缓冲区
  if (!(ret % 6))        //6个数据为一簇打印
   puts("");
  printf("%.2X ", rx[ret]);
 }
 puts("");
}

static void print_usage(const char *prog)   //参数错误则打印帮助信息
{
 printf("Usage: %s [-DsbdlHOLC3]\n", prog);
 puts("  -D --device   device to use (default /dev/spidev1.1)\n"
      "  -s --speed    max speed (Hz)\n"
      "  -d --delay    delay (usec)\n"
      "  -b --bpw      bits per word \n"
      "  -l --loop     loopback\n"
      "  -H --cpha     clock phase\n"
      "  -O --cpol     clock polarity\n"
      "  -L --lsb      least significant bit first\n"
      "  -C --cs-high  chip select active high\n"
      "  -3 --3wire    SI/SO signals shared\n");
 exit(1);
}

static void parse_opts(int argc, char *argv[])
{
 while (1) {
  static const struct option lopts[] = {
   { "device",  1, 0, 'D' },
   { "speed",   1, 0, 's' },
   { "delay",   1, 0, 'd' },
   { "bpw",     1, 0, 'b' },
   { "loop",    0, 0, 'l' },
   { "cpha",    0, 0, 'H' },
   { "cpol",    0, 0, 'O' },
   { "lsb",     0, 0, 'L' },
   { "cs-high", 0, 0, 'C' },
   { "3wire",   0, 0, '3' },
   { "no-cs",   0, 0, 'N' },
   { "ready",   0, 0, 'R' },
   { NULL, 0, 0, 0 },
  };
  int c;

  c = getopt_long(argc, argv, "D:s:d:b:lHOLC3NR", lopts, NULL);

  if (c == -1)
   break;

  switch (c) {
  case 'D':
   device = optarg;
   break;
  case 's':
   speed = atoi(optarg);
   break;
  case 'd':
   delay = atoi(optarg);
   break;
  case 'b':
   bits = atoi(optarg);
   break;
  case 'l':
   mode |= SPI_LOOP;
   break;
  case 'H':
   mode |= SPI_CPHA;
   break;
  case 'O':
   mode |= SPI_CPOL;
   break;
  case 'L':
   mode |= SPI_LSB_FIRST;
   break;
  case 'C':
   mode |= SPI_CS_HIGH;
   break;
  case '3':
   mode |= SPI_3WIRE;
   break;
  case 'N':
   mode |= SPI_NO_CS;
   break;
  case 'R':
   mode |= SPI_READY;
   break;
  default:
   print_usage(argv[0]);
   break;
  }
 }
}

int main(int argc, char *argv[])
{
 int ret = 0;
 int fd;

  int count=0;
  char buf[]={0x11,0x22,0x33,0x44,0x55};

 parse_opts(argc, argv);

 fd = open(device, O_RDWR);
 if (fd < 0)
  pabort("can't open device");

 /*
  * 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);

 while(1)
 {
  //经过测试，mosi发送数据正确，但是mosi没有直连miso脚，也能收到数据，怎么回事?
  //用示波器测量miso脚，也没有接收到数据波形，默认高电平
  transfer(fd);   //传输测试  
  sleep(1);
  transfer(fd);   //传输测试
  sleep(1);
  
  

    //count=write(fd,buf,sizeof(buf)/sizeof(buf[0]));
    //read(fd,buf,count);  
    //printf("read byte is: 0x%02X\n",buf[0]);
  //sleep(1);     
  
  
 }
 

 close(fd);

 return ret;
}