Parsing data from serial port

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Daniel
Daniel 2016-4-11
评论： Daniel 2016-4-19
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
  2 个评论
Walter Roberson
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
Daniel 2016-4-11
编辑：Walter Roberson 2016-4-11
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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Walter Roberson
Walter Roberson 2016-4-11
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
  6 个评论
显示 4更早的评论
Walter Roberson
Walter Roberson 2016-4-14
"persistent". Or a shared variable if you need to be able to reset the state.
Daniel
Daniel 2016-4-19
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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