linux spi test application

Here is a very simple demo application that shows how to read the Flash ID from an SPI Flash device:

/*
* Sample application that makes use of the SPIDEV interface
* to access an SPI slave device. Specifically, this sample
* reads a Device ID of a JEDEC-compliant SPI Flash device.
*/

#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>

int main(int argc, char **argv)
{
/*
* This assumes that a 'mdev -s' has been run to create
* /dev/spidev* devices after the kernel bootstrap.
* First number is the "bus" (SPI contoller id), second number
* is the "chip select" of the specific SPI slave
* ...
* char *name = "/dev/spidev1.1";
*/
char *name;
int fd;
struct spi_ioc_transfer xfer[2];
unsigned char buf[32], *bp;
int len, status;

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

memset(xfer, 0, sizeof xfer);
memset(buf, 0, sizeof buf);
len = sizeof buf;

/*
* Send a GetID command
*/
buf[0] = 0x9f;
len = 6;
xfer[0].tx_buf = (unsigned long)buf;
xfer[0].len = 1;

xfer[1].rx_buf = (unsigned long) buf;
xfer[1].len = 6;

status = ioctl(fd, SPI_IOC_MESSAGE(2), xfer);
if (status < 0) {
perror("SPI_IOC_MESSAGE");
return;
}
printf("response(%d): ", status);
for (bp = buf; len; len--)
printf("%02x ", *bp++);
printf("\n");
}

Here is how the application runs on the STM32F4 target:

~ # /spidev_flash /dev/spidev3.0
response(7): 20 20 16 10 00 00
~ #

SPI输出数据的同时必将读回数据来，因为要读回6个数据来，所以这里使用了缓冲区1的长度为6.