MATLAB: BytesAvailable doesnt empty Buffer completely

bufferbytesavailablefcnserial

Hello,

I have Problems reading all Data from the Buffer with BytesAvailableFcn. When Data is put in the buffer very fast, I have Data left in the Buffer but the BytesAvailableFcn doesnt trigger.

I programmed a Gui in Matlab which reads data froma an Arduino. The Arduino sends blocks of 8 Bytes. The BytesAvailableFcn is configured this way:

handles.serialIn = serial(COM3,'BaudRate',115200); 
set(handles.serialIn,'BytesAvailableFcnMode','byte'); 
set(handles.serialIn,'BytesAvailableFcnCount',8); 
fopen(handles.serialIn); 
set(handles.serialIn,'BytesAvailableFcn', {@mycallback,hObject});

When 8 Bytes are available the function mycallback reads 8 Bytes and processes them.

 function mycallback(obj,event,hObject)  
inByte = fread(obj,8,'char'); 
% process inByte

When the Arduino stops sending Data and I controll the Buffer manually, most of the time there ist still Data in there (more than 8 Byte).

It would be nice if someone could help me here.

Thanks,

Alex

Best Answer

Your callback can look at the BytesAvailable property to find out how many bytes are present, possibly reading full groups of 8 bytes in one go, or looping in your callback until less than 8 bytes are available.

Related Solutions

MATLAB: How to empty the serial port buffer in MATLAB without using the Instrument Control Toolbox

One way to clear the contents of the serial port buffer is to do a simple

fscanf(serialobj)

to read everything in the buffer until the first terminator, which is 'LF' by default. If there is a terminator in the buffer before the last character of the buffer then the previous code will not clear the buffer completely.

Alternatively, you can read the available bytes in the buffer of the serialobj

and use the following code:

fread(serialobj, serialobj.BytesAvailable)

to read all the contents of the buffer. It should be noted that FREAD will return data in the binary format (as opposed to ASCII).

Disconnecting and then reconnecting to the serial object via FCLOSE and FOPEN will also flush the serial buffer. However this approach is computationally much less efficient than the solutions above.

MATLAB: Read bytes from putc CCS to matlab gui

function [queryfcn, removefcn] = buffer_bytes(s)
   persistent byte_buffer
   persistent buffer_count
   
   if isempty(buffer_count)
       byte_buffer = [];
       buffer_count = 0;
   end
   s.BytesAvailableFcnMode = 'byte';
   s.BytesAvailableFcnCount = 1;
   s.BytesAvailableFcn = @mycallback;
   queryfcn = @query_buffer;
   removefcn = @query_remove;
   
   function mycallback(obj,event,handles)
     current_bytes = fread(s, s.BytesAvailable);
     num_bytes = length(current_bytes);
     byte_buffer(buffer_count+1:buffer_count+num_bytes) = current_bytes;
     buffer_count = buffer_count + num_bytes;
   end
    function buffer = query_buffer(maxn)
        if nargin < 1 || maxn > buffer_count
            maxn = buffer_count;
        end
        buffer = bytes_buffer(1:maxn);
    end
    function query_remove(count)
        if count >= buffer_count
            byte_buffer = [];
            buffer_count = 0;
        else
            byte_buffer(1:count) = [];
            buffer_count = buffer_count - count;
        end
    end
 end

You call buffer_bytes, passing in the serial object. You get back a pair of function handles, queryfcn and removefcn; and bytes start to be buffered in the background as they arrive.

At any time, you call the first handle that was returned, the query function. If you do not pass in any parameter, then the output of the query function is a copy of all of the bytes that are currently queued. If you pass in a parameter, then at most that many bytes will be returned, with fewer returned if that was all that was available.

At any time, you call the second handle that was returned the removefcn. You must pass in a parameter, which is a count of the number of bytes to remove from the internal buffer. Bytes are left in the buffer until they are removed -- so if you call the query function multiple times, then the same bytes will be returned until you tell the remove function to discard them.

Not that I would bother with any of this stuff myself. instead I would just query s.BytesAvailable to find out whether there were at least 2 bytes available, and fread(s, 2, 'uint8') when it was time to fetch them.

Best Answer

Related Solutions

MATLAB: How to empty the serial port buffer in MATLAB without using the Instrument Control Toolbox

MATLAB: Read bytes from putc CCS to matlab gui

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