linux的spi驱动，测试自发自收的时候，没有短接也能收到发送的数据？

[蜗牛哦]

你好，关于spi驱动，
我移植好后，测试spi自发自收数据，现在没有把发送脚和接收脚连起来，怎么也能收到发送的数据？
A8平台的mosi和miso脚没有短接，怎么也能收到发送的数据呢？用示波器测量mosi脚有数据输出，证明有数据输出，但是miso脚没有数据输入，一直是高电平，可是为什么程序能收到数据呢？

以下spi测试程序：

/************************************************************
 1.SPI_IOC_RD_MODE     				//读 模式 
 2.SPI_IOC_RD_LSB_FIRST    			//读 LSB 
 3.SPI_IOC_RD_BITS_PER_WORD    		//读 每字多少位 
 4.SPI_IOC_RD_MAX_SPEED_HZ 			//读 最大速率 
 5.SPI_IOC_WR_MODE     				//写 模式 
 6.SPI_IOC_WR_LSB_FIRST    			//写 LSB 
 7.SPI_IOC_WR_BITS_PER_WORD    		//写 每字多少位 
 8.SPI_IOC_WR_MAX_SPEED_HZ 			//写 最大速率 
 9.SPI_IOC_MESSAGE(n)      			//传输n个数据包 
*************************************************************/








#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);
		
		

    //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;
}

[蜗牛哦]

测试程序是没有问题的，因为把测试程序放在arm9开发板工作正常。 [root@yj423 yj423]#./spidev_test spi mode: 0 bits per word: 8 max speed: 1000 Hz (1 KHz) FF FF FF FF FF FF 40 00 00 00 00 95 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF DE AD BE EF BA AD F0 0D 断开发送脚和接收脚 [root@yj423 yj423]#./spidev_test spi mode: 0 bits per word: 8 max speed: 1000 Hz (1 KHz) 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

[happy小文字]

建议自己看下底层方案厂商配置的spi读写操作那一部分，有可能出了问题，如果你的硬件上确实没有短接

[kasuel]

楼主我遇到了跟你一样的问题，不知道您最终解决这个问题了吗？

[boylinxing]

我也是。。。。。。

[小v电子]

我也是 imx6ul的开发板

[qq_36453489]

应该是你的板子上的MISO管脚接了个上拉电阻，所以默认点评就是高电平了