Styjun

I am working on voltmeter application, that draws voltage waveform. Hardware sends 1000 numbers (range 0 - 1023, always whole numbers) in string format per second through serial port.

public SerialPort serialPort = new SerialPort("COM3", 57600);
serialPort.Open();

String is converted into int and then drawn with DrawLine into PictureBox.

// variable declarations, all is int, runs in its own thread
while (blToMeasure) // true after clicking on button

 iPrevY = iY;
 iY = Int16.Parse(serialPort.ReadLine());
 graphicsGraph.DrawLine(penBlack, iX, iPrevY, iX + 1, iY);
 // only this thread is accessing PictureBox
 iX++;

 if (iX > picBoxGraph.Width)
 
 graphicsGraph.Clear(SystemColors.Control);
 iX = 0;
 

 if (iY > picBoxGraph.Height)
 

 

Issue is that drawing lines itself is fast as it should be only for a couple of seconds, but gets gradually slower.

I tried Int.Parse, Int32.Parse and splitting thread function multiple ways using lock (graphicsGraph) (moving conditions with Clear into another thread) or using BlockingCollection<int> (moving DrawLine into another thread, away from Parse). Nothing seems to work and app still gets slower a couple of times after like a minute of running.

There isn't issue with hardware itself, checked with another software. Is this too fast for C#?

Solution:

I got the best results using Port.ReadTimeout = 1 and Port.DiscardInBuffer(). Also using Form.DoubleBuffered = true, but it doesn't make a huge difference in this particular case.

// constructor
Port.ReadTimeout = 1;
Form.DoubleBuffered = true;

Here is the loop itself:

btn.Click() // click to start measuring

 Port.DiscardInBuffer();
 blToMeasure = true;


while (blToMeasure) // true after clicking on button

 iPrevY = iY;
 try 
 iY = Int16.Parse(serialPort.ReadLine());
 
 catch
 
 // exception logic
 
 graphicsGraph.DrawLine(penBlack, iX, iPrevY, iX + 1, iY);
 // only this thread is accessing PictureBox
 iX++;

 if (iX > picBoxGraph.Width)
 
 graphicsGraph.Clear(SystemColors.Control);
 iX = 0;
 

 if (iY > picBoxGraph.Height)
 

 

When the app starts to read from the port, there is always accumulated data, because my hardware is sending numbers all the time, so I get rid of the buffer. Than the drawing of lines is not executed in differing spikes and the speed is constant. Analyzing the issue with Watch, I found out, that it occasionaly takes much longer to read this data and because of 1000 reads per second, it slows down. So to prevent slowing down, I used Port.ReadTimeout, that skips the read, if it takes too long.

The difference is visible, drawing no longer slows down and it keeps the same pace for minutes from what I've tried. I consider this sufficient solution for my issue, thank you!