c - RFID RC522读卡接线Pi

Question

我正在使用 raspberyy pi 3，RFID RC522。我想使用 WiringPi 来读取卡片。我正在尝试这段代码；

#include<stdio.h>
#include<conio.h>
#include<wiringPi.h>
#include<wiringPiSPI.h>

int main()
{
    int chan = 1;
    int speed = 1000000;

    if (wiringPiSPISetup(chan, speed) == -1)
    {
        printf("Could not initialise SPI\n");
        return;
    }
    printf("When ready hit enter.\n");
    (void) getchar(); // remove the CR
    unsigned char buff[100];

    while (1)
    {
        int ret = wiringPiSPIDataRW(chan, buff, 4);
        printf("%d %s \n", ret, buff);

    }
}

当我尝试这个时，它总是变成“4”。怎么读都看不懂。

Answer 1

您正在向从属 SPI 设备发送未初始化的数据。

unsigned char buff[100];

while (1)
{
    int ret = wiringPiSPIDataRW(chan, buff, 4);
    printf("%d %s \n", ret, buff);

}

缓冲区内容不确定。

查看library doc

int wiringPiSPIDataRW (int channel, unsigned char *data, int len);

This performs a simultaneous write/read transaction over the selected SPI bus. Data that was in your buffer is overwritten by data returned from the SPI bus.

这意味着您应该使用要发送的消息来初始化缓冲区。该数据将丢失，因为从机回复将返回到同一缓冲区中。

查看this example你应该做一些类似的事情:

 unsigned char buff[100] = {0};

 // Following bytes must be set according to your slave SPI device docs.
 buffer[0] = ??; 
 buffer[1] = ??;
 buffer[2] = ??;
 buffer[3] = ??;
 wiringPiSPIDataRW(chan, buffer, 4);