c# - 如何设置树莓派串口波特率？

Question

我有以下 .NET Core 2.0 C# 代码:

using System;
using System.Runtime.InteropServices;

namespace TestSerial
{
    class Program
    {
        [Flags]
        public enum OpenFlags
        {
            O_RDONLY = 0,
            O_WRONLY = 1,
            O_RDWR = 2,

            O_NONBLOCK = 4,
        }

        [DllImport("libc")]
        public static extern int cfsetspeed(byte[] termios_data, long speed);

        [DllImport("libc")]
        public static extern int tcgetattr(int fd, [Out] byte[] termios_data);

        [DllImport("libc")]
        public static extern int tcsetattr(int fd, int optional_actions, byte[] termios_data);

        [DllImport("libc")]
        public static extern int open(string pathname, OpenFlags flags);


        static void Main(string[] args)
        {
            const string serialDevice = "/dev/serial/by-id/usb-ELT_SENSOR_EK100_V1.0_SN000001-if00-port0";

            int fileDescriptor = open(serialDevice, OpenFlags.O_RDONLY | OpenFlags.O_NONBLOCK);
            Console.WriteLine($"Libc.open returned {fileDescriptor}");

            byte[] termiosData = new byte[256];

            int result = tcgetattr(fileDescriptor, termiosData);
            Console.WriteLine($"Libc.tcgetattr returned {result}");

            result = cfsetspeed(termiosData, 38400);
            Console.WriteLine($"Libc.cfsetspeed returned {result}");

            result = tcsetattr(fileDescriptor, 0, termiosData);
            Console.WriteLine($"Libc.tcsetattr returned {result}");
        }
    }
}

程序应该将 USB 串行端口的波特率更改为 38400。但是，程序没有按预期运行。

这是运行程序的输出:

Libc.open returned 18
Libc.tcgetattr returned 0
Libc.cfsetspeed returned -1
Libc.tcsetattr returned 0

我也仔细检查了串口设置，确实没有改变:

$ sudo stty -a -F /dev/serial/by-id/usb-ELT_SENSOR_EK100_V1.0_SN000001-if00-port0
speed 9600 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>;
eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R;
werase = ^W; lnext = ^V; discard = ^O; min = 1; time = 0;
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Libc.cfsetspeed 返回错误的原因可能是什么？

Answer 1

问题是 cfsetspeed 函数的速度参数声明中的数据类型(long)不正确。速度参数的数据类型应为 uint。

这是正确的代码:

using System;
using System.Runtime.InteropServices;

namespace TestSerial
{
    class Program
    {
        [Flags]
        public enum OpenFlags
        {
            O_RDONLY = 0,
            O_WRONLY = 1,
            O_RDWR = 2,

            O_NONBLOCK = 4,
        }

        [DllImport("libc")]
        public static extern int cfsetspeed(byte[] termios_data, uint speed);

        [DllImport("libc")]
        public static extern int tcgetattr(int fd, [Out] byte[] termios_data);

        [DllImport("libc")]
        public static extern int tcsetattr(int fd, int optional_actions, byte[] termios_data);

        [DllImport("libc")]
        public static extern int open(string pathname, OpenFlags flags);


        static void Main(string[] args)
        {
            const string serialDevice = "/dev/serial/by-id/usb-ELT_SENSOR_EK100_V1.0_SN000001-if00-port0";

            int fileDescriptor = open(serialDevice, OpenFlags.O_RDONLY | OpenFlags.O_NONBLOCK);
            Console.WriteLine($"Libc.open returned {fileDescriptor}");

            byte[] termiosData = new byte[256];

            int result = tcgetattr(fileDescriptor, termiosData);
            Console.WriteLine($"Libc.tcgetattr returned {result}");

            result = cfsetspeed(termiosData, 38400);
            Console.WriteLine($"Libc.cfsetspeed returned {result}");

            result = tcsetattr(fileDescriptor, 0, termiosData);
            Console.WriteLine($"Libc.tcsetattr returned {result}");
        }
    }
}