CODEWITHSUNDEEP
pythonpyserialuart
Alex I
Alex I

Reputation: 20287

Read from two serial ports asynchronously

I'd like to read from two (or more) serial ports (/dev/ttyUSB0 etc) at the same time in python on Linux. I want to read complete lines from each port (whichever has data) and process the results in the order received (without race conditions). As a simple example could just write the lines to a single merged file.

I assume the way to do this is based on pyserial, but I can't quite figure out how to do it. Pyserial has non-blocking reads using asyncio and using threads. Asyncio is marked as experimental. I assume there wouldn't be any race conditions if the processing is done in asyncio.Protocol.data_received(). In the case of threads, the processing would probably have to be protected by a mutex.

Perhaps this can also be done not in pyserial. The two serial ports can be opened as files and then read from when data is available using select().

Upvotes: 0

Views: 11752

Answers (3)

Johann Chang
Johann Chang

Reputation: 1391

Consider using aioserial.

Here's an example:

import asyncio
import concurrent.futures
import queue

import aioserial


async def readline_and_put_to_queue(
        aioserial_instance: aioserial.AioSerial,
        q: queue.Queue):
    while True:
        q.put(await aioserial_instance.readline_async())


async def process_queue(q: queue.Queue):
    with concurrent.futures.ThreadPoolExecutor(max_workers=1) as executor:
        while True:
            line: bytes = await asyncio.get_running_loop().run_in_executor(
                    executor, q.get)
            print(line.decode(errors='ignore'), end='', flush=True)
            q.task_done()


q: queue.Queue = queue.Queue()
aioserial_ttyUSB0: aioserial.AioSerial = \
        aioserial.AioSerial(port='/dev/ttyUSB0')
aioserial_ttyUSB1: aioserial.AioSerial = \
        aioserial.AioSerial(port='/dev/ttyUSB1', baudrate=115200)

asyncio.run(asyncio.wait([
    readline_and_put_to_queue(aioserial_ttyUSB0, q),
    readline_and_put_to_queue(aioserial_ttyUSB1, q),
    process_queue(q),
]))

Upvotes: 4

Alex I
Alex I

Reputation: 20287

As suggested by @AlexHall in a comment, here is a solution that uses one thread for each serial port and a queue to synchronize access:

import serial
import Queue
import threading

queue = Queue.Queue(1000)

def serial_read(s):
    while True:
        line = s.readline()
        queue.put(line)

serial0 = serial.Serial('/dev/ttyUSB0')
serial1 = serial.Serial('/dev/ttyUSB1')

thread1 = threading.Thread(target=serial_read, args=(serial0,),).start()
thread2 = threading.Thread(target=serial_read, args=(serial1,),).start()

while True:
    line = queue.get(True, 1)
    print line

It may be possible to write this more elegantly, but it works.

Upvotes: 3

Giorgio B
Giorgio B

Reputation: 193

You could try to take the values in order and memorise it in variables:

a = data1.read ()
b = data2.read ()

And after process it in order:

If len (a) != 0 or len (b ) != 0:
             Process a
             Process b

Using this method if one or both of the value has data, process it

Upvotes: 0

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