Introduction

I wanted to communicate serially with Raspberry Pi, so I tried communication using USB serial conversion. I referred to "I tried serial communication with Raspberry Pi". A reception timeout has been added to the reception processing on the assumption that the processing will be performed in the order of command transmission → command reception.

environment

Raspberry Pi3
Python 3.7.2
pySerial 3.4

Installation

--Enter the following command to install pySerial. --Installation of pipenv is omitted.

$ pipenv install pyserial

USB serial conversion

I used FT232 USB serial conversion cable. If it is equipped with the FT232 chip, it seems to be recognized without adding a driver.

Check the connection destination with the following command.

$ ls -la /dev/ttyUSB*

If it is the first unit, the connection destination will be'/ dev / ttyUSB0'.

note: When communicating with Rasberry Pi on a PC (Windows / Mac / Linux), use a crossover cable. Since the Rasberry Pi is also a PC, there is a cross cable between the PCs, and the connection with communication equipment is straight (often).

code

Serial communication class

--It is assumed that processing is performed in the order of command transmission → command reception. (With timeout) --You can explicitly open / close the serial port. (Because it was necessary for personal implementation)

`sample.py`


# -*- coding: utf-8 -*-

import serial
import time
import threading

"""
Serial communication class
"""
class SampleComm:
    #Initialization
    def __init__(self):
        #Open flag
        self.isPortOpen = False
        #received data
        self.recvData = bytearray()
        #Event generation
        self.event = threading.Event()

    #Waiting for data reception(With timeout[sec])
    def recv(self, timeout=3):
        #Get time for timeout
        time_start = time.time()
        time_end = time_start
        #Clear thread waiting event
        self.event.clear()
        #Clear received data
        self.recvData.clear()
        #Received result True:Success False:Failure(time out)
        result = False

        #Waiting for data reception
        while not self.event.is_set():
            #Time-out check
            time_end = time.time()
            if (time_end - time_start > timeout):
                #Data transmission / reception stopped and failed(time out)To
                result = False
                self.stop()
                print("timeout:{0}sec".format(timeout))
                break

            #Read received data
            buff = self.comm.read()

            #Received data judgment
            if len(buff) > 0:
                #Add received data
                self.recvData.extend(buff)
                # (Temporary)Success if \ n has been received
                if (self.recvData.find(b'\n')) >= 0:
                    #Stop sending and receiving data and make it successful
                    result = True
                    self.stop()
                    break

        #Returns the result
        return (result, self.recvData)

    #Data transmission
    def send(self, data):
        self.comm.write(data)

    #Stop data transmission / reception
    def stop(self):
        self.event.set()

    #Cyril port open
    def open(self, tty, baud='115200'):
        try:
            self.comm = serial.Serial(tty, baud, timeout=0.1)
            self.isPortOpen = True
        except Exception as e:
            self.isPortOpen = False

        return self.isPortOpen

    #Serial port closed(Explicitly close)
    def close(self):
        self.stop()
        if (self.isPortOpen):
            self.comm.close()
        self.isPortOpen = False

if __name__ == "__main__":
    #Open serial
    comm = SampleComm()
    comm.open('/dev/ttyUSB0', '115200')

    #Data transmission
    comm.send('test'.encode())
    #Data reception(time out=10sec)
    result, data = comm.recv(10)
    print(result)
    print(data)

    #Close serial
    comm.close();

how to use

In pySerial version 2.5 and above, the argument of write () is bytearray (). If you want to send a string, do the appropriate encode (). str.encode () defaults to'utf-8'.

#Open serial
comm = SampleComm()
comm.open('/dev/ttyUSB0', '115200')

#Data transmission
comm.send('sample'.encode())
#Data reception(time out=10sec)
result, data = comm.recv(10)
print(result)
print(data)

#Close serial
comm.close();

You can also check the operation by executing sample.py.

$ python sample.py

in conclusion

Communication with the device is often processed in the order of command transmission → command reception, and I made it because I wanted to execute the reception processing with a timeout. It is necessary to change the judgment of reception completion as appropriate. I hope it will be helpful for similar cases in serial communication.

Serial communication with Raspberry Pi + PySerial