ret = ioctl(fd, SPI_IOC_MESSAGE(1), &tr_txrx[0])
时间: 2024-06-01 20:10:59 浏览: 15
&spi_transfer);
This line of code is using the ioctl system call to send a message to the SPI device specified by the file descriptor "fd". The message being sent is a single transfer defined by the spi_transfer structure, which contains information such as the data to be sent and received, the length of the transfer, and various configuration options. The SPI_IOC_MESSAGE macro is used to specify that this is a single transfer operation. The return value of the ioctl call is stored in the variable "ret".
相关问题
write code for spi communication using c/c++
Sure, here's an example code for SPI communication using C/C++:
```
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/spi/spidev.h>
#define SPI_DEVICE "/dev/spidev0.0"
#define SPI_MODE SPI_MODE_0
#define SPI_BITS_PER_WORD 8
#define SPI_SPEED_HZ 1000000
int spi_fd;
int spi_init()
{
int ret = 0;
spi_fd = open(SPI_DEVICE, O_RDWR);
if (spi_fd < 0) {
perror("open");
return -1;
}
uint8_t mode = SPI_MODE;
ret = ioctl(spi_fd, SPI_IOC_WR_MODE, &mode);
if (ret < 0) {
perror("ioctl");
return -1;
}
uint8_t bits_per_word = SPI_BITS_PER_WORD;
ret = ioctl(spi_fd, SPI_IOC_WR_BITS_PER_WORD, &bits_per_word);
if (ret < 0) {
perror("ioctl");
return -1;
}
uint32_t speed_hz = SPI_SPEED_HZ;
ret = ioctl(spi_fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed_hz);
if (ret < 0) {
perror("ioctl");
return -1;
}
return 0;
}
int spi_transfer(uint8_t *tx_buf, uint8_t *rx_buf, size_t len)
{
struct spi_ioc_transfer transfer = {
.tx_buf = (unsigned long)tx_buf,
.rx_buf = (unsigned long)rx_buf,
.len = len,
.speed_hz = SPI_SPEED_HZ,
.bits_per_word = SPI_BITS_PER_WORD,
.delay_usecs = 0,
};
int ret = ioctl(spi_fd, SPI_IOC_MESSAGE(1), &transfer);
if (ret < 0) {
perror("ioctl");
return -1;
}
return 0;
}
int main()
{
int ret = spi_init();
if (ret < 0) {
printf("SPI initialization failed\n");
return -1;
}
uint8_t tx_buf[2] = {0x01, 0x02};
uint8_t rx_buf[2] = {0};
ret = spi_transfer(tx_buf, rx_buf, 2);
if (ret < 0) {
printf("SPI transfer failed\n");
return -1;
}
printf("Received data: 0x%02x 0x%02x\n", rx_buf[0], rx_buf[1]);
close(spi_fd);
return 0;
}
```
This code initializes the SPI device and performs a SPI transfer with a 2-byte transmit buffer and a 2-byte receive buffer. The received data is printed to the console.
如何通过c语言去验证SPI的功能正确性
要验证SPI的功能正确性,通常需要以下步骤:
1. 确定SPI的主从模式、数据传输速率、数据位数等参数。
2. 编写SPI的驱动程序,包括初始化SPI、发送数据、接收数据等功能。
3. 编写测试程序,通过SPI发送数据给设备,然后读取设备返回的数据,并进行比较,以验证数据传输的正确性。
以下是一个简单的SPI测试程序的示例代码:
```c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/spi/spidev.h>
#define SPI_DEVICE "/dev/spidev0.0"
#define MODE 0
#define SPEED 1000000
#define BITS_PER_WORD 8
int main()
{
int spi_fd;
int ret;
unsigned char tx_buf[5] = {0x01, 0x02, 0x03, 0x04, 0x05};
unsigned char rx_buf[5] = {0};
struct spi_ioc_transfer spi;
spi_fd = open(SPI_DEVICE, O_RDWR);
if (spi_fd < 0) {
perror("Fail to open spi device");
exit(EXIT_FAILURE);
}
ret = ioctl(spi_fd, SPI_IOC_WR_MODE, &MODE);
if (ret < 0) {
perror("Fail to set spi mode");
exit(EXIT_FAILURE);
}
ret = ioctl(spi_fd, SPI_IOC_WR_BITS_PER_WORD, &BITS_PER_WORD);
if (ret < 0) {
perror("Fail to set spi bits per word");
exit(EXIT_FAILURE);
}
ret = ioctl(spi_fd, SPI_IOC_WR_MAX_SPEED_HZ, &SPEED);
if (ret < 0) {
perror("Fail to set spi speed");
exit(EXIT_FAILURE);
}
spi.tx_buf = (unsigned long)tx_buf;
spi.rx_buf = (unsigned long)rx_buf;
spi.len = sizeof(tx_buf);
spi.speed_hz = SPEED;
spi.bits_per_word = BITS_PER_WORD;
ret = ioctl(spi_fd, SPI_IOC_MESSAGE(1), &spi);
if (ret < 0) {
perror("Fail to send spi message");
exit(EXIT_FAILURE);
}
printf("Send data: ");
for (int i = 0; i < sizeof(tx_buf); i++) {
printf("%02x ", tx_buf[i]);
}
printf("\n");
printf("Receive data: ");
for (int i = 0; i < sizeof(rx_buf); i++) {
printf("%02x ", rx_buf[i]);
}
printf("\n");
close(spi_fd);
return 0;
}
```
该程序使用了Linux下的SPI设备节点/dev/spidev0.0,并设置了SPI的模式为0、速率为1MHz、每个字节8位。程序发送了一个5字节的数据包给设备,并读取设备返回的数据包。程序运行后,可以通过查看输出结果来判断SPI的功能是否正常。