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%% Try requesting answer until it is ready

    % Usually one should issue the LSWrite command, then keep requesting
    % the I2C bus-status with LSGetStatus until it doesn't return an error
    % and until the amount of bytes one requested is availabled, and then
    % finally retrieve the data with LSRead.
    %
    % I found that the step with LSGetStatus can be omitted. Each direct
    % command, including LSRead, has its own error message included (the
    % statusbyte). If instead of using LSGetStatus and THEN using LSRead,
    % we just use LSRead straight ahead, this has 2 advantages:
    % - most of the time, the I2C sensor is ready anyway. So we save the
    % time (especially via Bluetooth) that LSGetStatus needs.
    % - if the sensor is not ready, we can keep polling it with LSRead. The
    % error messages are the same, but once they stop (and data is ready),
    % we already got the data as payload - having saved another call!
    %
    % Compared to the traditional way, this yields a speed up of about 100%
    % for both Bluetooth and USB.
    %
    %
    % Note that there is a tiny chance for further improvement, depending
    % on the sensor. If we add a short pause here in the magnitude of 1ms
    % to 10ms, it could lead to one failed LSRead being saved. Imagine
    % this: Instead of asking the sensor straight away if it's ready, and
    % then waiting 60ms for one more Bluetooth packet to arrive, we could
    % wait 10ms (if that is enough) and then get the sensors answer with
    % the next packet straight away.
    % Testing showed that this is NOT necessary and most of the time NOT
    % helping with Bluetooth, a fast computer and the ultrasonic sensor.
    % However, different sensors may show different behaviour... 

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    % use a timeout so we don't get stuck
    startTime = clock();
    timeOut = 1; % in seconds
    status = -1; % initialize

    BytesRead = 0;
    
    % if we get error 224, it seems the sensor was not opened properly
    % or, alternatively, it was opened, but due to termination of a NXC
    % program, it was "closed" again... so let's warn about this, but only
    % once...
    ShowedWarning224 = false;
    
%% Actual request-loop
    timedOut = false;
    while ((status ~= 0) || ( BytesRead < 1)) 

        % note that we suppress statusbyte-error-warnings by requesting the
        % 3rd optional output argument of NXT_LSRead()
        [data BytesRead status] = NXT_LSRead(Port, handle);

        % discovery: if we get an error 221, it seems there is nothing that
        % can be done to retrieve the data. we will run into a timeout. so
        % why not retry the whole reading process?
        if (status == 221)  % 221 = "Communication bus error"
                        
            if isdebug()
                textOut(sprintf(['! COM_ReadI2C failed, recursion depth ' num2str(RecursionDepth) ' @ ' datestr(now, 'HH:MM:SS.FFF') '\n']))
            end%if
            
            % recursively retry this whole thing!
            ReturnBytes = COM_ReadI2C(Port, RequestLen, DeviceAddress, RegisterAddress, handle, RecursionDepth + 1);
            
            return 
            
        elseif (status == 224) % 224 = "Specified channel/connection not configured or busy"
            
            % for this error, we do nothing but showing a warning once...
            if (RecursionDepth == 1) && (ShowedWarning224 == false)
                warning('MATLAB:RWTHMindstormsNXT:Sensor:I2CnotConfiguredOrBusy', 'It seems the specified digital sensor is either busy or was not opened properly. If rebooting the NXT does not help, make sure the correct Open* command for this sensor has been executed, and no NXC/NBC program running on the brick has been terminated (or is currently being terminated) before/while sensor data are read. Trying to continue...');
                ShowedWarning224 = true;
            end%if
            
        end%if
        
        % already timed out?
        if etime(clock, startTime) > timeOut
            timedOut = true;
            break
        end%if
        
    end%while

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    % Check for maximum recursion depth! This can happen when this function
    % repeatedly cannot read valid data via I2C. We set it by hand to 3
    % tries. This condition will happen when for example you pull out the
    % sensorcable of the US sensor just while it is retrieving data...
    if RecursionDepth > 3
        return
    end%if

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% see http://www.hitechnic.com for more register information
% retrieve 14 bytes from device 0x02, register 0x42 - 0x4F
% in mode 0 only the first 4 bytes are needed
lng = 14;
if mode == 0
       lng = 4;
end
  
%waitUntilI2CReady(port, handle);
data = COM_ReadI2C(port, lng, uint8(2), uint8(66), handle);

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% retrieve 2 bytes from device 0x02, register 0x44   
    data = COM_ReadI2C(port, 2, uint8(2), uint8(68), handle);

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% retrieve 6 bytes from device 0x02, register 0x42
    data = COM_ReadI2C(port, 6, uint8(2), uint8(66), handle);

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%% Get sensor data
    waitUntilI2CReady(port, handle);
    % read 5 bytes from register 0x42
    data = COM_ReadI2C(port, 5, uint8(4), uint8(66));
    datahex = dec2hex(data);