microbit serial communication splits text into lines

Question

I am a beginner with the microbit and I have tried to copy some code from different tutorials/code examples. I am just trying to set up the serial communication between a computer and the microbit. My plan is to have the microbit just echo every line it receives and send it back for now. But the lines are split and I am not sure if it is the microbit or the computer doing the splitting. I have tried from two different computers with the same result.

Here is the microbit code:

from microbit import *

uart.init(baudrate=115200)

msg_str = ""
while True:
    msg_bytes = uart.readline()
    if (msg_bytes):
        print(msg_bytes)

My computer code, a Python program with pyserial:

import serial
import serial.tools.list_ports as list_ports

def find_microbit_comport():
    ports = list(list_ports.comports())
    for p in ports:
        if (p.pid == 516) and (p.vid == 3368):
            return str(p.device)

if __name__ == '__main__':
    ser = serial.Serial()
    ser.baudrate = 115200
    ser.timeout = 1
    ser.port = find_microbit_comport()
    ser.open()
    ser.write(b'testing')
    text = ser.readline()
    while text != b'':
        print(text.decode('utf-8'))
        text = ser.readline()
    ser.close()

The problem I have that is that it prints out this:

b'te'

b'sting'

I was expecting it to print b'testing' in one word. I could write code to combine the text, but I could then get out of sync.

Oppy · Accepted Answer · 2020-02-04T13:38:40.210

I replicated your results using python 3.5 on Linux and a microbit.

I modified the Python code slightly. Please find this below:

import serial
import serial.tools.list_ports as list_ports

def find_microbit_comport():
    ports = list(list_ports.comports())
    for p in ports:
        if (p.pid == 516) and (p.vid == 3368):
            return str(p.device)

if __name__ == '__main__':
    print('running code')
    ser = serial.Serial()
    ser.baudrate = 115200
    ser.timeout = 1
    ser.port = find_microbit_comport()
    ser.open()
    ser.write('hello there\n')
    ser.close()
    ser.open()
    text = ser.readline()
    while (1):
        print(text.decode('utf-8'))
        text = ser.readline()
    ser.close()

Try this as the micropython on your microbit:

from microbit import *

uart.init(baudrate=115200)

msg_str = 'out: '.strip()
while True:
    new_byte = (uart.read(1))
    if new_byte == None:
        continue
    new_char = str(new_byte, 'UTF-8')
    msg_str += new_char
    if ("\n" in msg_str):
        print(msg_str)
        msg_str = ''

Output:

running code
out:hello there

This reads one byte at a time until a newline character is found, appending each byte onto the output string. The danger is that the newline character is dropped during transmission through the serial port. It is robust over a wired connection. If using wireless transmission, characters are easily corrupted or missed.

I would like to adjust the uart.init timeout parameter to see if this would fix the issue. This is not available in micropython on the microbit at this time.

but why did the OP's implementation not work correctly? the documentation states that readline() waits for a newline character. so, why it returns before a newline is found? — obe, Feb 03 '20 at 22:53
It might be something to do with the uart timing out. The timout parameter for uart.init is not available with the implementation of micropython on the microbit to test this. — Oppy, Feb 04 '20 at 13:39
I thought about that, but https://microbit-micropython.readthedocs.io/en/latest/uart.html says: "Return value: the line read or None on timeout.". So in case of timeout I'd expect "None"... — obe, Feb 04 '20 at 13:42
thanks, it at least fixes my problem. I do not completely understand why my code did not work but your answers above might be the correct — RustyJuggler, Feb 08 '20 at 14:27

microbit serial communication splits text into lines

1 Answers1