C＃串口有条件和部分读取

Question

I am stumped. Searched myself blue in the face - no go.

I am trying to establish serial comms with a device that sends 2 different blocks of data (one after the other) every 1 second continuously. The first block starts with "PID" and the second block ends with "H18".

I only need to read once every 5 seconds.

My problem is two fold:

1. I have no idea/control when the read starts and often starts mid - block.
2. I have no control over the start and end cycle to ensure I get a full two blocks as I need both.

Both blocks are about 200 characters long in total, has no /r at the beginning and has /r/n in between various items.

I have tried doing two subsequent reads but no success. Tried playing with StartsWith and EndsWith but they are not recognized? The code has been all over the show, but here is the base I am working from currently:

static void DataReceivedHandlerbat(object sender,     SerialDataReceivedEventArgs e)
    {
        var batm = sender as SerialPort;
        if ((batm != null) && (!_gotResponse))
        {
         while (stringb.Length < 200)
            {
                byte[] buffer = new byte[batm.BytesToRead];
                int numRead = batm.Read(buffer, 0, buffer.Length);
                stringb.Append(System.Text.Encoding.ASCII.GetString(buffer));

               // if (stringb.S  == 0)
                //{
                  //   _gotResponse = true;
                    // break;
                //}
              }
         }
    }

and

 /// Obtain Battery string

            SerialPort batm = new SerialPort();
            batm.PortName = "com4";
            batm.BaudRate = 19200;
            batm.DataBits = 8;
            batm.Parity = Parity.None;
            batm.StopBits = StopBits.One;

            batm.DataReceived += new SerialDataReceivedEventHandler(DataReceivedHandlerbat);

            batm.Open();

            //batm.ReadExisting();

            int timeoutMsb;
            timeoutMsb = 1000;

            var startTimeb = DateTime.Now;
            while (!_gotResponse && ((DateTime.Now - startTimeb).TotalMilliseconds < timeoutMsb))
            {
                Thread.Sleep(20);
            }

            batm.Close();

            _gotResponse = false;

            //Build Battery String

            String bat = stringb.ToString();

Please help me - I am fairly new to C# and have struggled for 4 days with this?

Answer 1

Is this a GUI application or a background service? Either way, ditch DataReceived event and use ReadAsync , as I showed in my blog post . Then, buffer all incoming data into a List<byte> (this easily deals with messages which arrive split into two), and implement some synchronization logic.

Here's an outline of how synchronization works:

1. loop through the List<byte> , find the beginning of a message
2. determine whether the entire message has been received
3. copy the message payload and fire off an event so the business logic that acts on the message can be separate from the buffering/parsing logic
4. remove bytes from the list up to the end of the detected message
5. search the remainder of the buffer for more valid messages (repeat 1-4)
6. when the buffer List<byte> doesn't contain a complete message, call ReadAsync again