USB comm between RP2040 and Python

[CodreanuML]

Hello,

i am using this script on my rp2040 :

import select
import sys
import time

Set up the poll object

poll_obj = select.poll()
poll_obj.register(sys.stdin, select.POLLIN)

Loop indefinitely

while True:
# Wait for input on stdin
poll_results = poll_obj.poll(1) # the '1' is how long it will wait for message before looping again (in microseconds)
if poll_results:
# Read the data from stdin (read data coming from PC)
data = sys.stdin.readline().strip()
# Write the data to the input file
sys.stdout.write("received data: " + data + "\r")
else:
# do something if no message received (like feed a watchdog timer)
continue

I use it to communicate with a python script on my computer:

def main():
s = serial.Serial(port="/dev/ttyACM0", parity=serial.PARITY_EVEN, stopbits=serial.STOPBITS_ONE, timeout=1)
s.flush()

#
#s.open()
s.write("TESTMESSAGE".encode())
mes = s.read_until().strip()
print(mes.decode())
print(len(mes))
s.close()

I don't know why sometimes it works...sometimes not.

Strange is that the python script on my computer don't throw an error. The port is open everything is fine .But if what i seen is that when it won't work mycropython script don't enter inside IF statement .

Can anybody help to undestand why ?

[shariltumin]

These scripts are working fine for me, so please feel free to give them a try.

Python:

# Python3
import serial

def main(cnt):
   s.write(f"#{cnt} TESTMESSAGE\n".encode())
   s.flush()
   mes = s.readline()
   print(mes.decode(), end='')

#device="/dev/ttyUSB0"
device="/dev/ttyACM0"
s = serial.Serial(port=device, baudrate=9600, bytesize=8, parity='N', stopbits=1, timeout=None, xonxoff=False, rtscts=False, dsrdtr=False)
print(device,s)

cnt=1
while cnt<100:
   main(cnt)
   cnt+=1

MicroPython:

# MicroPython
import select, sys, os

# Set up the poll object
poll_obj = select.poll()
poll_obj.register(sys.stdin, select.POLLIN)

dp = os.dupterm(None) # disassociate REPL from terminal in/out

# Loop indefinitely until CRTL+C
while True:
   # Wait for input on stdin
   poll_results = poll_obj.poll(100) # 100 microseconds timeout
   if poll_results:
      # Read the data from stdin (read data coming from PC), use readline()
      data = sys.stdin.readline()[:-1] # strip '\n'
      if data: # Write the data to the input file
         sys.stdout.write("received data: " + data + '\n')
   else:
      continue

os.dupterm(dp) # restore REPL

There are a few differences from your scripts. I use os.dupterm(None) to disassociate REPL from the terminal in/out.

[glenn20]

I'm not sure why it works sometimes and not others, but one thing I notice is that you use readline() and read_until() which both expect to find a \n character at the end of messages and, as far as I can see in the scripts above, you don't terminate your messages with a '\n' character.