Parsing data from serial port

Question

Daniel 2016-4-11

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/278320-parsing-data-from-serial-port

评论： Daniel 2016-4-19

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

Hi,

I communicate with a DsPIC

i have a constant format for a message:

HEADER1 HEADER2 OPCODE DATA CHECKSUM (no spaces)

in my MATLAB GUI i want to read the incoming message, chk if i get the HEADER1 I EXPCT, then chk to see i get HEADER2 i expect , if so: get OPCODE and DATA and do with that something

how can i split my message?

thought about switch;case

wanted to know if there is something more "elegant"

Thanks

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Walter Roberson 2016-4-11

Is that a text format or a numeric format? are the headers variable length? How can you tell when HEADER1 stops and HEADER2 begins?

Daniel 2016-4-11

编辑：Walter Roberson 2016-4-11

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headers ARE FIXED

header1: 55
header2: AA

if i get a sequence of 55AA i know now comes the opcode then the data

if i get 55555555555 i wait for AA because HEADER1 was recieved

if i get 55AF i wait to get 55 again because sequence 55AA was not recieved

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Answer 1

Walter Roberson 2016-4-11

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You need a Finite State Machine. The Mathworks tools for that are http://www.mathworks.com/discovery/finite-state-machine.html but you probably do not need anywhere near the full power of that.

current_state = 0;
while true
   this_input = fread(s, 1, 'uint8');
   if feof(s); break; end
   if state == 0 && this_input == 88   %0x55
      current_state = 1;
   elseif current_state == 1 && this_input == 170   %0xAA
      current_state = 2;
      now read the opcode and data and so on.
      When you are through with it
      current_state = 0;
   else
      current_state = 0;
   end
 end

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Daniel 2016-4-12

编辑：Daniel 2016-4-12

在 MATLAB Online 中打开

ok, so here is what i tried: i have a button ('READ') that is intended to check if any message exist in the buffer. analyze the message i.e. check if the message is valid (HEADERs) GET THE OPCODE, and according to opcode - write to 3 different boxes. example:

    55  AA  02 1B CHKSUM
    H1  H2  OP DATA CHKSUM
OPCODE 02 : write to box 'temperature' 27(0X1B)
OPCDODE 03: write to box 'voltage' the DATA

BUT NOTHING APPEARS IN THE BOX... here is my actual code for the button 'READ' press:

%%--- Executes on button press in rxButton.
function rxButton_Callback(hObject, eventdata, handles)
current_state = 0;
while (handles.SerPIC.BytesAvailable >= 5)
  this_input = fread(handles.SerPIC,1, 'uint8');
%     if feof(SerPIC);
%         break;
%     end
    switch current_state
        case 0 % state 0  wait for HEADER_1
            if (this_input == 85)
                current_state = 1;
            else 
                current_state = 0;
            end
        case 1 % state 1  wait for HEADER_2
            if (this_input == 170) %was 170
                current_state = 2;
                recieved_checksum = 255;
            elseif (this_input == 85)
                current_state = 1;
            else
                current_state = 0;
            end 
        case 2 % state 2  wait for OPCODE
             OPCODE = this_input;
             current_state = 3;
             recieved_checksum = mod(recieved_checksum + this_input,255);
        case 3 % state 3  wait for DATA
             DATA = this_input;
             current_state = 4;
             recieved_checksum = mod(recieved_checksum + this_input,256);
        case 4 % state 4  wait for CHECKSUM
             current_state = 0;
             recieved_checksum = recieved_checksum - this_input;
             if (recieved_checksum == 0)
                % data is valid and can be read
                if (OPCODE == 2)
                    set(handles.temp_read,'string',(DATA))
                elseif (OPCODE == 3)
                    set(handles.voltage_read,'string',DATA)
                elseif (OPCODE == 4)
                    set(handles.current_read,'string',DATA)
                end
             end
    end
end
guidata(hObject,handles)
end

Walter Roberson 2016-4-14

"persistent". Or a shared variable if you need to be able to reset the state.

Daniel 2016-4-19

在 MATLAB Online 中打开

I'll try here: so i set in the "connect" button the following:

 handles.SerPIC.BytesAvailableFcn = {'@intcon1',handles};
    set(handles.SerPIC,'BytesAvailableFcnMode','byte');  
    set(handles.SerPIC,'BytesAvailableFcnCount', 1);

and the call back function is:

if true
function  intcon1(hObject, eventdata, handles)
  persistent current_state
  persistent L;
  persistent i;
  persistent DATA;
  persistent recieved_checksum;
  % current_state = 0;
  % while (handles.SerPIC.BytesAvailable >= 1)
      this_input = fread(handles.SerPIC,1);
      switch current_state
          case 0 % state 0  wait for HEADER_1
              L=0;
              i=0;
              DATA=0;
              recieved_checksum=0;
              if (this_input == 85)
                  current_state = 1;  
              else 
                  current_state = 0;
              end
          case 1 % state 1  wait for HEADER_2
              if (this_input == 51) %was 170
                  current_state = 2;
                  recieved_checksum = 136;
              elseif (this_input == 85)
                  current_state = 1;
              else
                  current_state = 0;
              end 
          case 2 % state 2  wait for message length
               MESSAGE_LENGTH = this_input;
               L=MESSAGE_LENGTH;
               i=1;
               current_state = 3;
               recieved_checksum = mod(recieved_checksum + this_input,255);
          case 3
  %         if (s.BytesAvailable == MESSAGE_LENGTH)
              DATA(i) = this_input;
              recieved_checksum = mod(recieved_checksum + this_input,255);
              i=i+1;
              L = L - 1;
              if L > 0
                  current_state = 3;
              else
                  current_state = 4;
              end
          case 4
                recieved_checksum = recieved_checksum - this_input;
                if (recieved_checksum ==0)
                    set(handles.temp_read,'string',[num2str(DATA(1))])
                    set(handles.voltage_read,'string',[num2str(DATA(2))])
                    set(handles.current_read,'string',[num2str(DATA(3))])
                      current_state = 0;
                else
                    current_state = 0;
                end
      end
          guidata(hObject,handles)
end

but nothing seems to happen. and i get an error:

if true
Error using feval
Invalid function name '@intcon1'.
  Error in instrcb (line 36)
          feval(val{1}, obj, eventStruct, val{2:end});
  Warning: The BytesAvailableFcn is being disabled. To enable the callback property
  either connect to the hardware with FOPEN or set the BytesAvailableFcn property.  
end

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