Reading from arduino's serial port using go-serial

Question

I have arduino uno with simple firmware which provides simple API over serial port:

Command "read" returns the current state
Command "on" sets the state to "on"
Command "off" sets the state to "off"

Now I want to implement a client for this device. If I use Arduino IDE serial monitor, this API works as expected. If I use python with pySerial library, API works.

But whenever I try to read data from the serial port using golang and go-serial, my read calls hangs (but works fine with /dev/pts/X created by socat, for example)

Python client

import serial
s = serial.Serial("/dev/ttyACM0")
s.write("read\n")
resp = []
char = None
while char != "\r":
    char = s.read()
    resp.append(char)
print "".join(resp)

Go client (hangs on Read call forever): package main

import "fmt"
import "github.com/jacobsa/go-serial/serial"

func check(err error) {
    if err != nil {
        panic(err.Error())
    }
}

func main() {
    options := serial.OpenOptions{
        PortName:        "/dev/ttyACM0",
        BaudRate:        19200,
        DataBits:        8,
        StopBits:        1,
        MinimumReadSize: 4,
    }
    port, err := serial.Open(options)
    check(err)
    n, err := port.Write([]byte("read\n"))
    check(err)
    fmt.Println("Written", n)
    buf := make([]byte, 100)
    n, err = port.Read(buf)
    check(err)
    fmt.Println("Readen", n)
    fmt.Println(string(buf))
}

Firmware code:

String inputString = "";         // a String to hold incoming data
boolean stringComplete = false;  // whether the string is complete
String state = "off";

void setup() {
    // initialize serial:
    Serial.begin(9600);
    // reserve 200 bytes for the inputString:
    inputString.reserve(200);
    pinMode(13, OUTPUT);
}

void loop() {
    // print the string when a newline arrives:
    if (stringComplete) {
        blink();
        if (inputString == "on\n") {
        state = "on";  
        } else if (inputString == "off\n") {
        state = "off";  
        } else if (inputString == "read\n") {
        Serial.println(state  );  
        }
        // clear the string:
        inputString = "";
        stringComplete = false;
    }
}


void blink() {
    digitalWrite(13, HIGH);   // set the LED on
    delay(1000);              // wait for a second
    digitalWrite(13, LOW);    // set the LED off
    delay(1000);              // wait for a second
}

void serialEvent() {
    while (Serial.available()) {
        // get the new byte:
        char inChar = (char)Serial.read();
        // add it to the inputString:
        inputString += inChar;
        // if the incoming character is a newline, set a flag so the main loop can
        // do something about it:
        if (inChar == '\n') {
        stringComplete = true;
        }
    }
}

Python code

My only guess: You've set a minimum read size of 4. If there are fewer than 4 bytes read, will it block? — Flimzy
Serial.println() equal to on python ser.readline() (so your delimiter is \n) another point is : C++ and python no diference, like ` while (Serial.available())(ardu) == while True: while ser.inWaiting() > 0: (python)` — dsgdfg
@dsgdfg yes, I could replace this code with ser.readline(), without while loop, but my intend is to have golang version working, python code is for example, that device is working at all. — Mikhail
@Flimzy I have tried with minimum size equals 1, still nothing. — Mikhail
"/dev/ttyACM0" and "/dev/ttyACM1" I hope it's a joke. — dsgdfg

Nitro Nitro · Accepted Answer · 2018-05-14T12:46:19

You have set the baud rate for the Go lang function to 19200, but in the arduino you have used 9600.

In the python code, the baud rate is not set, so it takes the default of 9600.

Just set the right baud rate in your go lang program, and it should work.

Reading from arduino's serial port using go-serial

1 Answers