Unable to read from Serial Port using C# Mono (RaspberryPi)
Solution 1
Have a look at stty command. It will let you set/read teminal settings
http://linux.about.com/od/lna_guide/a/gdelna38t01.htm will give a rundown on it's use. It would be easier to call out to than minicom, and the settings stay on the device.
Solution 2
I have done something like the same as you before. I had to read and write data through USB Serial adapter, and didnt use minicom. It may not be god code but i found that inorder to read the data I could create a new thread and have that check for data, my code include a lot of stuff but basicly i did this:
System.Threading.Thread newThread;
newThread = new System.Threading.Thread(this.check_get_data);
and the check_get_data method
public void check_get_data ()
{
byte tmpByte = 0;
while (m_objSerialPort.BytesToRead != 0) {
tmpByte = (byte)m_objSerialPort.ReadByte ();
DoSomethingWithByte(tmpByte);
Thread.Sleep(20);
}
}
this is currently running with two usbserials. dont know if it helps but hope you find your solution
Admin
Updated on June 04, 2022Comments
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Admin almost 2 years
I'm attempting to write a C# library which looks at all available USB serial ports on a Raspberry Pi so that I can enumerate, identify and communicate with a set of Arduinos connected to the Pi via a USB hub.
I am able to make this work on my windows machine (several Arduinos connected to my desktop computer) and have even been able to make it work on my Pi however, I am struggling to understand how to generalize the fix.
If I attempt to run the program by itself on the Pi, I am able to open the serial port and send data however, I cannot receive anything from the Arduinos: I get timeout exceptions. I understand that Mono's implementation of SerialPort is limited and I must use SerialPort.ReadByte() instead of Readline() and the data received events (my solution is based on code from HowToSystemIOPorts). My Serial port enumeration is using a method outlined in another stack exchange response here.
My timeout is currently set to 4 seconds, which is several orders of magnitude longer than I expect to receive the message.
After a lot of googling, I came across mention of using minicom to initialize the serial port here, which to my surprise allowed me to receive data from the Arduino. The biggest drawback is that I need to initialize the port using minicom and leave the process opening each time I boot the Pi. I also can't seem to figure out how to make this work with multiple Arduinos.
Here is what I have tried so far:
- Updated the Pi firmware and software to their latest versions
- Attempted to use both an Arduino MEGA 2560 R3 and Arduino UNO
- Changed the owner of the tty* ports (ttyACM0 and ttyUSB0 in this case) to both my user and group
- Successfully configured the port via minicom, left the process running and start the program and read/wrote data. A manual process which only seems to work for one Arduino at a time
- Successfully run the program in Windows without fault
- Verified the Arduinos are recognized by the Pi running "dmesg | grep tty"
Here is what I hope to solve:
- Automatic setup/initialization of the Arduino serial ports. Whether through a shell script run before the main program or within Mono code so that the code below can run as intended.
Here is my connection code:
public bool StartArduinoComms() { string[] ports = GetPortNames(); foreach (string port in ports) { mLogger.LogMessage(ProsthesisCore.Utility.Logger.LoggerChannels.Arduino, string.Format("Found serial port {0}", port)); } bool foundCorrectArduino = false; var idPacket = new ArduinoMessageBase(); idPacket.ID = ArduinoMessageValues.kIdentifyValue; string jsonOutput = Newtonsoft.Json.JsonConvert.SerializeObject(idPacket); foreach (string port in ports) { SerialPort serialPort = new SerialPort(port, kArduinoCommsBaudRate); serialPort.Parity = Parity.None; serialPort.DataBits = 8; serialPort.StopBits = StopBits.One; //Only check unopened ports if (!serialPort.IsOpen) { serialPort.Open(); //Disable telemtry just incase var toggle = new { ID = ArduinoMessageValues.kTelemetryEnableValue, EN = false }; string disableTelem = Newtonsoft.Json.JsonConvert.SerializeObject(toggle); serialPort.Write(disableTelem); //Discard any built up data serialPort.DiscardInBuffer(); serialPort.Write(jsonOutput); serialPort.ReadTimeout = kIDTimeoutMilliseconds; string response = string.Empty; for (int i = 0; i < kNumRetries; ++i) { try { //This is guaranteed to timeout if not configured through minicom response = ReadLine(serialPort); break; } //Catch case where the serial port is unavailable. MOve to next port catch (TimeoutException) { continue; } } if (!string.IsNullOrEmpty(response)) { //Perform response validation } else { //Got no response } if (!foundCorrectArduino) { serialPort.Close(); } } } return foundCorrectArduino; } /// <summary> /// From https://stackoverflow.com/questions/434494/serial-port-rs232-in-mono-for-multiple-platforms /// </summary> /// <returns></returns> private static string[] GetPortNames() { int p = (int)Environment.OSVersion.Platform; List<string> serial_ports = new List<string>(); // Are we on Unix? if (p == 4 || p == 128 || p == 6) { string[] ttys = System.IO.Directory.GetFiles("/dev/", "tty*"); foreach (string dev in ttys) { //Arduino MEGAs show up as ttyACM due to their different USB<->RS232 chips if (dev.StartsWith("/dev/ttyS") || dev.StartsWith("/dev/ttyUSB") || dev.StartsWith("/dev/ttyACM")) { serial_ports.Add(dev); } } } else { serial_ports.AddRange(SerialPort.GetPortNames()); } return serial_ports.ToArray(); }