Serial port on C#, read until a byte sequence

Question

I have a stream of data from a COM port. This stream is composed of sets of 30 bytes. The first 26 bytes are the information and the last four is a set of 0xFFF. For example, a set of array is [0xFF,0x5A,0x44,0x15,...,0x5F,0xFF,0xFF,0xFF,0xFF]. In the first 26 byte there is no possibility to get a similar sequence.
Thus, I do not find any method in C# in order to "read until". The piece of C# code that I use to read serial data is:

    public static int count;
    public static void Main()
    {
        SerialPort mySerialPort = new SerialPort("COM8");

        mySerialPort.BaudRate = 250000;
        mySerialPort.Parity = Parity.None;
        mySerialPort.StopBits = StopBits.One;
        mySerialPort.DataBits = 8;

        mySerialPort.Handshake = Handshake.None;
        mySerialPort.DtrEnable = true;
        mySerialPort.RtsEnable = true;
        mySerialPort.DataReceived += new SerialDataReceivedEventHandler(DataReceivedHandler);

        mySerialPort.Open();

        count = 0;

        Console.WriteLine("Press any key to continue...");
        Console.WriteLine();

        Console.ReadKey();
        mySerialPort.Close();
    }


    private static void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e)
    {
        SerialPort sp = (SerialPort)sender;
        string indata = sp.ReadExisting();
        count++;
    }

Is there another way in order to get a List<> of 26 interesting bytes? Considering that the data are on an Arduino and I can edit the Arduino code and my Arduino sends around 800 bytes sets each second. The Arduino code, if you are interested, is (at this moment run under Arduino Due):

#define MAX_ADC_RESOLUTION 12 

int val;
void setup() {


 Serial.begin(250000);

 analogReadResolution(MAX_ADC_RESOLUTION); //

  adc_init(ADC, SystemCoreClock, ADC_FREQ_MAX*2, 4); //~220000 samples per second, A/D readings OK

val = 0;


}


void loop() {  

 int start = millis();
 int num_samples = 0; //This identify the sample frequency

 while( millis() - start < 1000 )
 {


  for(int channel=0;channel<12;channel++){ //loop for each analog (0-11)

    val = analogRead(channel);
    val++;
    Serial.write((unsigned char)((val & 0xFF00) >> 8));
    Serial.write(((unsigned char)(val & 0x00FF)));    
  }
  Serial.write((unsigned char)((num_samples & 0xFF00) >> 8));
  Serial.write(((unsigned char)(num_samples & 0x00FF)));  
  Serial.write(0xFF);
  Serial.write(0xFF);
  Serial.write(0xFF);
  Serial.write(0xFF);

  num_samples++;
 }


}

Edit in order to explain better what is my problem:

If I set a simply length of buffered read I get a part of the incoming flow. So, the end control bytes can be placed everywhere in the array of bytes (e.g. I typically receive 0x44,0x53,...,0xFF,0xFF,0xFF,0xFF,..,0x55). In addition, suppose to receive a set as this: 0x22,...,0x00,0xFF,0xFF,0xFF,0xFF,0xFF. It is possible and my software will cut the last byte.

Strongly recommend [PInvokeSerialPort](https://github.com/ebraminio/PInvokeSerialPort), it fires one event for every byte, and more stable than .net built in one. — Lei Yang, Mar 03 '17 at 01:01
You need to buffer the data read, so that you can inspect it in the 30-byte chunks you are expecting. See marked duplicate for more details, as well as https://stackoverflow.com/questions/16439897/serialport-readbyte-int32-int32-is-not-blocking-but-i-want-it-to-how-do, https://stackoverflow.com/questions/24136264/c-sharp-serialport-not-receiving-all-the-bytes-in-a-single-transmission, https://stackoverflow.com/questions/13417442/serialport-communication-in-c-sharp-splitting-frames, and https://stackoverflow.com/questions/2604932/receiving-messages-part-by-part-from-serial-port-using-c-sharp — Peter Duniho, Mar 03 '17 at 01:54
If I set a simply length of buffered read I get a part of the incoming flow. So, the end control bytes can be placed everywhere in the array of bytes (e.g. I typically receive 0x44,0x53,...,0xFF,0xFF,0xFF,0xFF,..,0x55) — youngz, Mar 03 '17 at 08:30

score 1 · Answer 1 · answered Mar 03 '17 at 01:41

1

Why don't you use Read kinda like this:

byte[] buffer = new byte[30];
sp.Read(buffer, 0, 30);

This way you get the array of bytes and you can test for values you need/don't need.

answered Mar 03 '17 at 01:41

Jack

11
2

2

what happens when a read completes having read only 20 bytes, with the remaining 10 held up for some reason, to be read later? – Peter Duniho Mar 03 '17 at 01:49

Serial port on C#, read until a byte sequence

1 Answers1