C中通过UDP套接字的串行接口

Question

我是串行接口的新手，我的公司要求我设计一个 API 来配置陀螺仪 - 连接到 WIFI 芯片 - 使用 C 代码，通过 UDP 套接字发送十六进制命令到WIFI芯片。我确保遵守制造商手册提供的格式，但似乎在串行接口方面我遗漏了一些东西。我正在使用此代码来执行此操作：

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <netdb.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include "port.h"
#include <time.h>

void waitFor (unsigned int );

unsigned char head1 = 0xff; //head
unsigned char head2 = 0xaa;  //head2
unsigned char saveadd = 0x00; //saveconfig address
unsigned char savevalue = 0x00; //save config  0x01 is factory reset
unsigned char endd = 0x00; //end

int
main(int argc, char **argv)
{
    struct sockaddr_in myaddr;  /* our address */
    struct sockaddr_in remaddr; /* remote address */
    remaddr.sin_addr.s_addr = inet_addr("192.168.1.1");
    remaddr.sin_port = htons(8889);
    socklen_t addrlen = sizeof(remaddr);        /* length of addresses */
    int recvlen;            /* # bytes received */
    int fd;             /* our socket */
    int msgcnt = 0;         /* count # of messages we received */
    remaddr.sin_family = AF_INET;

    /* create a UDP socket */

    if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
        perror("cannot create socket\n");
        return 0;
    }

    /* bind the socket to any valid IP address and a specific port */

    memset((char *)&myaddr, 0, sizeof(myaddr));
    myaddr.sin_family = AF_INET;
    myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    myaddr.sin_port = htons(SERVICE_PORT);

    if (bind(fd, (struct sockaddr *)&myaddr, sizeof(myaddr)) < 0) {
        perror("bind failed");
        return 0;
    }



        printf("waiting on port %d\n", SERVICE_PORT);


        // Hex command that turns a builtin LED on
        unsigned char comPart1 =    0xFF;
        unsigned char comPart2 =    0xAA;
        unsigned char comPart3 =    0x1b;
        unsigned char comPart4 =    0x00;
        unsigned char comPart5 =    0x00;

        unsigned char commands [5]; /* unsigned char array to hold command */
        commands [0] = comPart1;
        commands [1] = comPart2;
        commands [2] = comPart3;
        commands [3] = comPart4;
        commands [4] = comPart5;




        unsigned char temp_buf [2]; /*buffer used to send hex command*/
        temp_buf [0]= (unsigned char) 0x00;
        temp_buf [1]= '[=10=]';



        for (int i = 0; i < 5 ; i++) 
        {
           temp_buf [0] = commands[i];

        if (sendto(fd, temp_buf, sizeof (temp_buf), 0, (struct sockaddr *)&remaddr, addrlen) < 0)
            perror("sendto");
       }

        waitFor (0.5); /*delay specified by user manual*/



        printf ("%s \n", "Now saving the configration");
        //save commands as specified by user manual 
        unsigned char saveConfig [5];

        saveConfig [0] = head1;
        saveConfig [1] = head2;
        saveConfig [2] = saveadd;
        saveConfig [3] = savevalue;
        saveConfig [4] = endd;

        for (int i = 0; i < 5 ; i++)
        {

        temp_buf [0] = saveConfig [i];

        if (sendto(fd, temp_buf, sizeof (temp_buf), 0, (struct sockaddr *)&remaddr, addrlen) < 0)
            perror("sendto");
            waitFor (0.05);
       }
       waitFor (0.45);



}

void waitFor (unsigned int secs) {
    unsigned int retTime = time(0) + secs;   // Get finishing time.
    while (time(0) < retTime);               // Loop until it arrives.
}

我能够使用 CuteCom 串行配置陀螺仪（如果断开与 WIFI 芯片的连接并连接到 USB-TTL） .所以我知道硬件可以工作。当谈到串行接口时，我错过了什么。如何完成这样的任务？

Answer 1

saveConfig 是二进制数据，但您需要发送 hex 表示形式，因此：

temp_buf [0] = saveConfig [i]

不会工作。

你需要的是：

unsigned int
gethex(unsigned int val,int shf)
{

    val >>= shf;
    val &= 0x0F;
    val = "0123456789ABCDEF"[val];

    return val;
}

temp_buf[0] = gethex(saveConfig[i],4);
temp_buf[1] = gethex(saveConfig[i],0);

Answer 2

你said/asked在评论

I am essentially trying to send the following: 0xff 0xaa 0x1b 0x00 0x00 one byte at a time. Do you think the NULL (byte of zeros) are causing the issue? How would I indicate the end of the buffer if I am not to use it?

但是，从您的代码中，您发送了一个 NULL 字节 in-between 每个数据字节。 temp_buf 包含 2 个字节，你是 hard-coding 第二个字节到 [=12=] 并将第一个字节设置为数据字节。然后 sendto(fd, temp_buf, sizeof (temp_buf), 0, (struct sockaddr *)&remaddr, addrlen 行发送这个缓冲区的内容。如果您将网络流量困在 wireshark 中，您会看到您正在发送 0xff 0x00 0xaa 0x00 0x1b 0x00 0x00 0x00 0x00 0x00 而不是您打算发送的内容。

为了回答您的问题，c 除了字符串之外，缓冲区的 NULL 字节终止符没有任何通用之处。有效数据字节可以一直为 0x00。如果我通过电子邮件向某人发送一张黑色图片，我将发送整个 0x00 字节流。您的陀螺仪必须具有某种应在其文档中描述的协议。根据我的经验，这是一个固定的消息长度，start/end 字节的 "magic" 序列，甚至是 application-defined header。在你的评论中，你表示陀螺仪一次只需要一个字节，所以你去吧，一次只发送一个字节！我想您将代码更改为如下所示：

// really no need for temp_buf
for (int i = 0; i < 5 ; i++)
{
  if (sendto(fd, &saveConfig[i] /* or saveConfig+i */, sizeof(char), 0, (struct sockaddr *)&remaddr, addrlen) < 0)
  {
    perror("sendto");
    // I'm guessing from your indentation you want this wait inside the if-statement. Note that in the code you posted, the if-statement doesn't have any brackets so this will execute each time through the loop whether there is an error or not
    waitFor (0.05);
  }
  waitFor (0.45);
}

一般来说，无论何时您处理此类网络问题，我都强烈建议您使用 wireshark（或等效工具）来准确查看您发送的内容，这非常有帮助！

C中通过UDP套接字的串行接口

Serial interface via UDP sockets in C

c

serialization

udp

serial-port

serial-communication