Matlab 实时读取串口并绘图

Vofa+

Vofa+ 是一个很好的跨平台上位机软件，但是它无法保存数据，而且作者也并没有要继续更新的意思，保存数据功能应该是遥遥无期了。因此本文使用 Matlab 实时读取串口数据，并使用 plot 函数绘制。

vofa+ 里发送 float 型数据的协议是 justfloat，其具体规则如下：

下位机发送数据

下位机发送程序各有不同，下面是一个例子，使用的是 DSP28027 单片机，定义了全局变量 gTime 做时间向量：

void myPutVariableData_vofa(void)
{
    int   num = 6; // number of float variables to be sent
    float data[6]      = {0}; // float variables to be sent 
    uint16_t txBuf[14] = {0}; 
    float testData = 114514.0;
    float testW    = 10.0;

    txBuf[2 * num]     = 0x0000;
    txBuf[2 * num + 1] = 0x7f80;
    
    data[0] = testData;
    data[1] = testData;
    data[2] = testData;
    data[3] = testData;
    data[4] = testData;
    data[5] = sin(2 * 3.1415 * testW * gTime);

    memcpy(txBuf, (uint16_t *)data, num * sizeof(float));
    mySCI_sendDataBlocking(txBuf, 2 * num + 2);
}

Matlab 代码

使用 matlab 读取串口主要分为接收数据和协议解析，用的方法比较粗暴，直接读取串口然后判断帧尾。

Step 1. 设置串口

Matlab 中使用 serialportlist 命令查找电脑连接的串口，找到对应设备名称后在设置相关参数

devicelist = serialportlist' % This command shows the port connected.

baudrate        = 115200;
device          = "/dev/cu.usbserial-A700eG4x";
myPort          = serialport(device,baudrate); 
myPort.DataBits = 8;
myPort.StopBits = 1;
myPort.Parity   = "none";

Step 2. 设置数据缓冲区

设置绘图数据的个数和时间窗口大小，本文设置 6 个数据， 2000 个采样点的窗口，每一帧传输时间使用 $dt=\frac{(n\ast 4+4)\ast 8\text{BIT}}{\text{Baudrate}}$ 计算，$n$ 为传输数据个数。然后将数据缓冲区都初始化为0：

varNum = 6;
buf    = 2000;
dt     = (varNum * 4 + 4) * 8 / baudrate;
time   = -dt*(buf/2):dt:dt*(buf/2-1);

dataBuf.var0 = zeros(buf,1);
dataBuf.var1 = zeros(buf,1);
dataBuf.var2 = zeros(buf,1);
dataBuf.var3 = zeros(buf,1);
dataBuf.var4 = zeros(buf,1);
dataBuf.var5 = zeros(buf,1);

这里也可以使用动态命名变量来初始化：

varNum = 6;
buf    = 2000;
dt     = (varNum * 4 + 4) * 8 / baudrate;
time   = -dt*(buf/2):dt:dt*(buf/2-1);


for i = 1:varNum
	namelist{i} = ['var',num2str(i-1)];
	dataBuf.(namelist{i}) = zeros(buf,1);
end

Step 3. 协议解析

协议解析主要是找到帧尾标志，使用 read() 读取4字节串口数据并判断是否是帧尾，找到帧尾就可以按照对应位置解析数据。转换 00 00 80 7F 为十进制数组 0 0 128 127 再进行判断，如果找到帧尾，就依次读取数据位（这里读取的是下一帧的数据，差一帧）。然后使用 circshift() 循环存储数据，让缓冲区的最后一位始终存储最新的数据。

因为数据是小端浮点数组（先发低位再发高位），所以使用 flip() 函数重新排序，然后将读取到的数据转换为 uint32，再使用 typecast() 函数转换为单精度浮点型数据。

dec2uint32 = @(dec)uint32(dec * [2^24, 2^16, 2^8, 2^0]');
temp = read(myPort,4,'uint8');
if prod(temp == [0 0 128 127])
    temp = read(myPort, varNum * 4, 'uint8');
    dataBuf.var0 = circshift(dataBuf.var0);
    dataBuf.var0(end) = typecast(dec2uint32(flip(temp(1:4))),'single');
    dataBuf.var1 = circshift(dataBuf.var1);
    dataBuf.var1(end) = typecast(dec2uint32(flip(temp(5:8))),'single');
    dataBuf.var2 = circshift(dataBuf.var2);
    dataBuf.var2(end) = typecast(dec2uint32(flip(temp(9:12))),'single');
    dataBuf.var3 = circshift(dataBuf.var3);
    dataBuf.var3(end) = typecast(dec2uint32(flip(temp(13:16))),'single');
    dataBuf.var4 = circshift(dataBuf.var4);
    dataBuf.var4(end) = typecast(dec2uint32(flip(temp(17:20))),'single');
    dataBuf.var5 = circshift(dataBuf.var5);
    dataBuf.var5(end) = typecast(dec2uint32(flip(temp(21:24))),'single');
end

同样这里可以使用动态变量命名简化代码：

temp = read(myPort,4,'uint8');
if prod(temp == [0 0 128 127])
    temp = read(myPort, varNum * 4, 'uint8');
    for i = 1:varNum
        dataBuf.(namelist{i})      = circshift(dataBuf.(namelist{i}),-1);
        dataBuf.(namelist{i})(end) = typecast(dec2uint32(flip(temp((i-1) * 4 + 1: i * 4))),'single');
    end
end

Step 4. 绘制数据

先建立 figure 对象，使用 while 判断窗体存在条件，持续绘制数据

h   = figure;
plotenabled = 0;

%%
while(ishandle(h))
    temp = read(myPort,4,'uint8');
    if prod(temp == [0 0 128 127])
        temp = read(myPort, varNum * 4, 'uint8');
        for i = 1:varNum
            dataBuf.(namelist{i})      = circshift(dataBuf.(namelist{i}),-1);
            dataBuf.(namelist{i})(end) = typecast(dec2uint32(flip(temp((i-1) * 4 + 1: i * 4))),'single');
        end
        plot(time, dataBuf.var5,'b-','LineWidth',1.5);
        if plotenabled == 0
            plotenabled = 1;
            grid on
            title('Matlab Serial Port Read','FontSize',14,'FontName','Times New Roman');
            xlabel('Time','FontSize',14,'FontName','Times New Roman');
            ylabel('Value','FontSize',14,'FontName','Times New Roman');
        end
    end
    plotenabled = 0;
end

• 变量 plotenabled 用于首次绘图设置绘图参数，只有第一次绘图的时候会执行设置 title, xlabel, ylabel 等参数。

完整的 Matlab 代码如下：

%---------------------------------------
% This is the series port read script
%
% hu 2023-07-07 Created
% hu 2024-04-10 Test vofa+ protocol
%---------------------------------------

clc,clear,close all
devicelist = serialportlist' % This command shows the port connected.

baudrate        = 115200;
device          = "/dev/cu.usbserial-A700eG4x";
myPort          = serialport(device,baudrate); 
myPort.DataBits = 8;
myPort.StopBits = 1;
myPort.Parity   = "none";

varNum   = 6;
buf      = 2000;
dt       = (varNum * 4 + 4) * 8 / baudrate;
time     = -dt*(buf/2):dt:dt*(buf/2 - 1);

for i = 1:varNum
    namelist{i} = ['var',num2str(i-1)];
    dataBuf.(namelist{i}) = zeros(buf,1);
end
dec2uint32 = @(dec)uint32(dec * [2^24, 2^16, 2^8, 2^0]');

h   = figure;
plotenabled = 0;

%%
while(ishandle(h))
    temp = read(myPort,4,'uint8');
    if prod(temp == [0 0 128 127])
        temp = read(myPort, varNum * 4, 'uint8');
        for i = 1:varNum
            dataBuf.(namelist{i})      = circshift(dataBuf.(namelist{i}),-1);
            dataBuf.(namelist{i})(end) = typecast(dec2uint32(flip(temp((i-1) * 4 + 1: i * 4))),'single');
        end
        plot(time, dataBuf.var5,'b-','LineWidth',1.5);
        if plotenabled == 0
            plotenabled = 1;
            grid on
            title('Matlab Serial Port Read','FontSize',14,'FontName','Times New Roman');
            xlabel('Time','FontSize',14,'FontName','Times New Roman');
            ylabel('Value','FontSize',14,'FontName','Times New Roman');
        end
    end
    plotenabled = 0;
end
clc,clear,close all

绘制数据可以通过 fig 窗口保存到本地，或者在数据转换后保存到工作区，这里不再赘述。