Raspberry pie serial port

Serial port usage routines and instructions ：http://elinux.org/Serial_port_programming

http://elinux.org/RPi_Serial_Connection

Pyserial API https://pyserial.readthedocs.io/en/latest/pyserial_api.html

sudo apt-get install python-serial

 

python -m serial.tools.list_ports  This command can view the file node of the device .

 

class serial.Serial  

  

    __init__(port=None, baudrate=9600, bytesize=EIGHTBITS, parity=PARITY_NONE, stopbits=STOPBITS_ONE, timeout=None, xonxoff=False, rtscts=False, writeTimeout=None, dsrdtr=False, interCharTimeout=None)  

 

port： Read or write port

baudrate： Baud rate

bytesize： Byte size

parity： Check bit

stopbits： Stop bit

timeout： Read timeout settings

writeTimeout： Write timeout

xonxoff： Software flow control

rtscts： Hardware flow control

dsrdtr： Hardware flow control

interCharTimeout: Character interval timeout

timeout  And read():

timeout = None Have been waiting for , Until the data is received

timeout = 0: Non blocking

timeout = x: The waiting time

write()  Default block , Unless write_timeout  Set up .

 

read(size=1)： Read from serial port size Bytes . Returns the data read . If a timeout is specified , It is possible to return fewer bytes after timeout ; If no timeout is specified , Will wait until the specified number of bytes is received .

write(data)： send out data, And return the number of bytes sent . If bytes and bytearray You can use （python 2.6 above ）, Then accept it as a parameter ; Otherwise, accept str As a parameter .

abnormal ：SerialTimeoutException—— This exception occurs when write timeout is configured and timeout occurs .

inWaiting()： Returns the number of bytes in the receive cache

routine ：

#!/usr/bin/env python

import serial
import time

def uart(port):
	rv_buf=""
	ch=''
	while True:
		ch=port.read();
		rv_buf+=ch
		if ch=='' or ch=='\r':
			return rv_buf			
			
send_buf=""
port=serial.Serial("/dev/ttyUSB0",baudrate=115200,timeout=None)
while True:
	send_buf=uart(port)
	port.write(send_buf)
	print(send_buf)

Accept data through serial port , We have successfully debugged the simple acceptance of single channel . But in the process of practical application , Multiple channels are required . So the current idea is to pass select To achieve .

First of all, let's simply learn python Medium select.

Python Of select() Method to call the IO Interface , It monitors sockets,open files, and pipes( All take fileno() Method ) When to become readable and writeable, Or communication errors .

 

Select Is very simple to use ,select( iwtd, owtd, ewtd[, timeout]) The first three parameters are ‘ Wait for the person ’. These three parameters are waiting for input in sequence 、 Output and abnormal state . Empty arrays are allowed timeout Parameter accepts the seconds represented by floating-point numbers . If omitted timeout Will block until at least one file descriptor is ready .timeout by 0 It means never blocking . Here is the blocking operation in the serial port receiving process , It's been blocking , Waiting for data , Prevent data loss .

The return value contains the prepared objects in the first three parameters 3 A list . If it has timed out but no object is ready , Then the return 3 An empty list

#!/usr/bin/env python

import select
import serial
import time
import multiprocessing 

def uart(port):
	rv_buf=""
	ch=''
	while True:
		ch=port.read()
		rv_buf+=ch
		if ch=='' or ch=='\r':
			return rv_buf			
			
def uart_trans():
	send_buf0=""
	send_buf1=""
	i=0
	port0=serial.Serial("/dev/myuart0",baudrate=115200,timeout=0)
	port1=serial.Serial("/dev/ttyUSB1",baudrate=115200,timeout=0)
	fd0=file("/dev/myuart0","r+")
	fd1=file("/dev/ttyUSB1","r+")
	while True:
		rlist,wlist,elist=select.select([fd0,fd1],[],[],)
		for fd in rlist:
			if(fd==fd0):
				send_buf0=uart(port0)
				port0.write(send_buf0)
			if(fd==fd1):
				send_buf1=uart(port1)
				port1.write(send_buf1)
if __name__ =="__main__":
	uart_trans()

Test source ：https://github.com/IJustLoveMyself/Raspberry-Pi/blob/master/test1/uart.py

https://github.com/IJustLoveMyself/Raspberry-Pi/blob/master/test1/select.py