背景

板子上有两个串口，但是串口1被xr829模块占用了，串口3主要用于调试，为简单实现串口功能，本讲将实现usb转串口（ch340）来采集gps的数据，并解析。

（一）USB串口驱动

@本讲不使用Tina系统，使用 百问Buildroot 。

Tips:CH340是CH341的阉割版，CH340不支持并口、打印口、IIC，专为串口应用设计

在buildroot已经集成了ch341的驱动，我们将其 使能 即可使用，非常简单。

Symbol: USB_SERIAL_CH341 [=y]                                                                                
   Type  : tristate                                                                                             
   Prompt: USB Winchiphead CH341 Single Port Serial Driver                                                      
     Location:                                                                                                  
       -> Device Drivers                                                                                        
         -> USB support (USB_SUPPORT [=y])                                                                      
   (1)     -> USB Serial Converter support (USB_SERIAL [=y])                                                    
     Defined at drivers/usb/serial/Kconfig:105                                                                  
     Depends on: USB_SUPPORT [=y] && USB [=y] && USB_SERIAL [=y]  
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（二）驱动加载

驱动是编译进内核的，不用手动加载，把USB转TTL插到USB口就自动匹配识别，生成ttyUSB0设备。
以下是开机显示信息：

[   11.529946] usbcore: registered new interface driver ch341
[   11.537840] usbserial: USB Serial support registered for ch341-uart
[   11.545934] ch341 1-1.2:1.0: ch341-uart converter detected
[   11.578483] usb 1-1.2: ch341-uart converter now attached to ttyUSB0
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ls /dev
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（三）简单读取串口数据

此时已经将ch340和gps模块连接上开发板了

使用 cat 命令即可简单读取串口返回的信息。

# cat /dev/ttyUSB0

A*7B

$GPVTG,,T,,M,1.070,N,1.982,K,A*27

$GPGGA,072008.00,2306.6$GPTXT,01,01,01,NMEA unknown msg*58

$GPRMC,072232.00,A,2306.62360,N,11316.59966,E,0.311,,020822,,,A*78

$GPVTG,,T,,M,0.311,N,0.577,K,A*25

$GPGGA,072232.00,2306.62360,N,11316.59966,E,1,08,1.62,21.7,M,-5.6,M,,*7A

$GPGSA,A,3,13,02,05,11,20,18,24,23,,,,,3.06,1.62,2.59*05

$GPGSV,3,1,11,02,49,126,20,05,43,034,37,11,28,123,12,13,58,033,35*72

$GPGSV,3,2,11,15,73,291,21,18,27,324,37,20,24,071,29,23,10,286,32*78

$GPGSV,3,3,11,24,26,175,20,29,48,259,10,30,06,046,*45

$GPGLL,2306.62360,N,11316.59966,E,072232.00,A,A*68
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（四）数据解析

本解析参考：https://blog.csdn.net/qq_30665009/article/details/121434507

我们在编写正式的应用程序之前，先了解这一堆数据里面我们想要的部分 --> $GPRMC
$GPRMC格式：

 $GPRMC,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>*hh

 $GPRMC,072232.00,A,2306.62360,N,11316.59966,E,0.311,,020822,,,A*78
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其中：

（五）编写应用程序

参考 https://www.likecs.com/show-205110023.html

1、定义结构体

typedef struct __gprmc__
{
    UINT time;         /* gps定位时间 */
    char pos_state;    /*gps状态位*/
    float latitude;    /*纬度 */
    float longitude;   /* 经度 */
    float speed;       /* 速度 */
    float direction;   /*航向 */
    UINT date;         /*日期  */
    float declination; /* 磁偏角 */
    char dd;
    char mode; /* GPS模式位 */
} GPRMC;
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2、使用 open 和 read 函数读取串口数据
3、获取想要的部分

/* 如果buff字符串中包含字符"$GPRMC"则将$GPRMC的地址赋值给ptr */
if (NULL == (ptr = strstr(buff, "$GPRMC")))
{
    return -1;
}
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4、使用 sscanf 进行格式化处理，存进结构体
5、计算、回显处理

（六）测试

编译后放到开发板，测试程序

# ls
gps_test

# ./gps_test
buff:1,13,36,033,33*7F
$GPGSV,3,2,10,15,62,356,30,18,48,324,20,20,14,092,19,23,21,306,23*7A
$GPGSV,3,3,10,24,48,164,20,29,35,229,25*70
$GPGLL,2306.62377,N,11316.59930,E,081227.00,A,A*65
$GPRMC,081228.00,A,2306.62398,N,11316.59935,E,0.294,,020822,,,A*72
$GPVTG,,T,,M,0.294,N,0.545,K,A*28
$GPGGA,081228.00,2306.62398,N,11316.59935,E,1,08,1.04,-0.4,M,-5.6,M,,*61
$GPGSA,A,3,15,18,24,13,05,02,23,20,,,,,2.10,1.04,1.82*02
$GPGSV,3,1,10,02,29,144,21,05,36,062,35,11,10,138,,13,36,033,32*7E
$GPGSV,3,2,10,15,62,356,30,18,48,324,17,20,14,092,20,23,21,306,22*75
$GPGSV,3,3,10,24,48,164,20,29,35,229,26*73
$GPGLL,2306.62398,N,11316.59935,E,081228.00,A,A*6E
$GPRMC,081229.00,A,2306.62396,N,11316.59928,E,0.427,,020822,,,A*7F
$GPVTG,,T,,M,0.427,N,0.791,K,A*2D
$GPGGA,081229.00,2306.62396,N,11316.59928,E,1,09,1.04,-0.8,M,-5.6,M,,*6F
$GPGSA,A,3,15,18,24,13,05,02,23,20,11,,,,2.10,1.04,1.82*02
$GPGSV,3,1,10,02,29,144,21,05,36,062,35,11,10,138,1,1144,15,05,36,062,36,11,10,138,12)▒▒
===========================================================
==
==   GPS state bit : A  [A:有效状态 V:无效状态]
==   GPS mode  bit : A  [A:自主定位 D:差分定位]
==   Date : 2022-08-02
==   Time : 16:12:28
==   纬度 : 北纬:23度6分37秒
==   经度 : 东经:113度16分35秒
==   速度 : 0.294  m/s
==
============================================================
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但是要留意，某些gps模块获取不到该字段的数据，需要将其对应修改匹配。

至此，测试完毕。
源码地址：
https://download.csdn.net/download/qq_46079439/86272180