Serial communication with matlab problem in writing

[bouvett]

Hi guys,
I have already read many of the links available on this forum and on the web in general, but unfortunately i still haven't solved the problem in my code - I'm sure a geek out there will solve this in minutes but i'm still a newbie unfortunately :sad: .

i am trying to read data from a serial port, process the data and then transferring it back serially. Now the read is surely right, but unfortunately when i go to write a problem arises. I am in actual fact calibrating a touch screen to a glcd.. now the transmission of data between the embedded board i am using and the matlab is wrong when i write back to the serial port but good when i just read.

The code is:

function touch_screen_calibration ()
%This function will calibrate the touch screen for the natural input
%calculator. What it does is to accept input serially from the glcd which
%will be of the form x,y and then provide a calibrated output x_cal,y_cal
%again serially to the fpga.

%calibration constants
x_d0 =12;
x_d1 =114;
x_d2 =63;

y_d0 =6;
y_d1 =30;
y_d2 =57;

% Opens a serial communication object
SPort=serial('COM7','BaudRate', 9600,'Parity', 'none','DataBits',8,'StopBits', 1);
set(SPort,'InputBufferSize',20480000);
set(SPort,'Timeout',0.00000001);
fopen(SPort)

coordinates = zeros(1,5000);
counter =1;

% asynchronous mode
SPort.ReadAsyncMode = 'continuous';
readasync(SPort);

%Setup calibration variables
cal_counter = 6; %used to keep track of which calibration point has been received
                 %and whether calibration is ready.               
A=0.0;
B=0.0;
C=0.0;
D=0.0;
E=0.0;
F=0.0;
K=0;

    while(1)
        IN_DATA=fread(SPort,1,'uchar');
    
        if(IN_DATA ~= -1)  
            IN_DATA
            
            switch (cal_counter)
                case 0
                    x_0 = IN_DATA;
                    cal_counter = cal_counter +1;
                case 1
                    y_0 = IN_DATA;
                    cal_counter = cal_counter +1;
                case 2
                    x_1 = IN_DATA;
                    cal_counter = cal_counter +1;
                case 3
                    y_1 = IN_DATA; 
                    cal_counter = cal_counter +1;
                case 4
                    x_2 = IN_DATA;
                    cal_counter = cal_counter +1;
                case 5
                    y_2 = IN_DATA;
                    cal_counter = cal_counter +1;
                    
                    K = (x_0 -x_2)*(y_1 - y_2) - (x_1 - x_2)*(y_0 - y_2);
                    
                    A = ((x_d0 - x_d2)*(y_1 - y_2) -(x_d1 - x_d2)*(y_0 - y_2))/K;
                    B = ((x_0 - x_2)*(x_d1 - x_d2) -(x_d0 - x_d2)*(x_1 - x_2))/K;
                    C = (y_0*(x_2*x_d1 - x_1*x_d2) + y_1*(x_0*x_d2 - x_2*x_d0) + y_2*(x_1*x_d0 - x_0*x_d1))/K;
                    
                    D = ((y_d0 - y_d2)*(y_1 - y_2) -(y_d1 - y_d2)*(y_0 - y_2))/K;
                    E = ((x_0 - x_2)*(y_d1 - y_d2) -(y_d0 - y_d2)*(x_1 - x_2))/K;
                    F = (y_0*(x_2*y_d1 - x_1*y_d2) + y_1*(x_0*y_d2 - x_2*y_d0) + y_2*(x_1*y_d0 - x_0*y_d1))/K;
                    
                case 6 %calibration ready therefore start reading X and Y co-cordinates
                    X = IN_DATA;
                    cal_counter = cal_counter +1;
                case 7
                    Y = IN_DATA;
           
                    if( (X<128  && X>=0) && (Y<64  && Y>=0))
                        %Process data and send it serially
                        %x_cal = A*X + B*Y + C;
                        %y_cal = D*X + E*Y + F;
                        
                        x_cal = X;
                        y_cal = Y;

                        coordinates(1,counter) = X;
                        coordinates(1,counter+1) = Y;

                        counter = counter +2;

                        %slow down transmission for send
                        stopasync(SPort);
                        set(SPort,'Timeout',1);
                        SPort.ReadAsyncMode = 'continuous';
                        %readasync(SPort);

                        x_cal = round(x_cal);
                        fwrite(SPort,x_cal);

                        y_cal = round(y_cal);
                        fwrite(SPort,y_cal);

                        stopasync(SPort);
                        set(SPort,'Timeout',0.00000001);
                        SPort.ReadAsyncMode = 'continuous';
                        %readasync(SPort);

                        cal_counter = cal_counter -1;
                        save  coordinates coordinates
                    end
                    
                    
                otherwise cal_counter = cal_counter; %dummy
                    
            end
        end
    end
end

i suspect that the problem is that i am all the time changing the timeout period. The reason for doing this is because i want to read the port continously but if i keep the same time out period for writing an error is returned.


Thanks for your time guys.

regards,
bouvett

---------- Post added at 21:20 ---------- Previous post was at 21:09 ----------

if i just write to the serial port without changing the timeout i get an error:


??? Error using ==> serial.fwrite at 199
A timeout or Ctrl-C occurred during the write operation.

Error in ==> touch_screen_calibration at 102
fwrite(SPort,x_cal);

I hope this helps as a clue.
thanks guys

---------- Post added at 21:30 ---------- Previous post was at 21:20 ----------

I have confirmed that the problem is whit how i am handling the timeout period. when i set the time out period to 0.01, i would not need to change it before writing to the serial port but unfortunately this is quite slow for my application.. so what i really need is a proper handling of the changing of the timeout period.


thanks again

---------- Post added at 22:37 ---------- Previous post was at 21:30 ----------

The error is very strange since it can read very fast but it cannot write that fast not even 5 times slower... this is constantly giving me a timeout error when trying to write to the serial port