c - UART 比较图表。比格尔骨

Question

我在尝试将 uart 输入数据(来自 GPS)与“$”进行比较以检测新包时遇到问题。我确信问题在于我如何操作 charRead 变量。我尝试了一千种方法，但可能由于我缺乏经验，我还没有弄清楚问题是什么。代码会编译并且数据会一直出现，但是一旦我将代码加载到 beaglebone 中，它就会堆积起来，但不会进入“if (charRead =='$')”。

提前谢谢您!

#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <time.h>
#include <iostream>
#include <termios.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <string.h>
#include <ctype.h>
#include <math.h>
#include <limits.h>
#include "Payload.h"


#define SLOTS "/sys/devices/bone_capemgr.9/slots"
#define CR         0x0d
#define SPACE     0x20
#define COMMA     0x2C
#define MAXSIZE    100
unsigned long time_data;
unsigned int button = 45;
int i,z =0, j=0, value;
int rx_length;


int main()
{
    //uart4 configuration using termios

    int fd;
    //unsigned char  *mess;
    unsigned int value = 0;

    gpio_export(button);

    //Wait until the button is pushed
        while (value != 1){
            if (z==0){
            printf("waiting\n");}
                    z++;
            gpio_get_value(button, &value);}



    //OPEN THE UART
    //open uart4 for tx/rx, not controlling device

        if((fd = open("/dev/ttyO4", O_RDONLY | O_NOCTTY|O_NONBLOCK)) < 0){
            printf("Unable to open uart4 access.\n");
            }
        termios uart4;
        cfsetospeed(&uart4, B9600); //Set the speed

        //set attributes of uart4
        uart4.c_iflag = 0;
        uart4.c_oflag = 0;
        uart4.c_lflag = 0;
        tcsetattr(fd, TCSANOW, &uart4);




        //----- CHECK FOR ANY RX BYTES -----
            // Read up to 100 characters from the port if they are there

            unsigned char stringRead[MAXSIZE];
            unsigned char charRead;


        do{

            if (rx_length = read(fd, (void*)charRead, MAXSIZE)>0){

                if (charRead =='$'){
                i=0;
                stringRead[i] = charRead; //Store in the first position of the char --> $
                do {
                        rx_length = read(fd, (void*)charRead, MAXSIZE); //Read the next bit
                        if( (charRead != '\0') ) { 
                        i++;
                        stringRead[i] = charRead; //write into stringRead
                            }
                } while(charRead != 'CR'); //ASCII Carriage Return
                    stringRead[i+1] = charRead;
                    printf("%s", stringRead);
                }}
            if (rx_length==0){
                //No data
            }

        gpio_get_value(button, &value);

        }while (value!=0);

    gpio_unexport(button);

close(fd);
return 0;
}

Answer 1

您传递的是 charRead 变量值的强制转换，而不是指向内存位置的指针，因为函数 read() 需要 void *.

read(fd, (void*)charRead, MAXSIZE)

您需要一次读取一个字符:

read(fd, &charRead, 1)

或者改变你的阅读逻辑，以最大限度地提高阅读量和数据处理量。我还建议在访问 stringRead 时添加边界检查。