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Thread: Teensy 3.5 detection problem with Raspberry Pi

  1. #1
    Junior Member
    Join Date
    May 2023
    Posts
    7

    Teensy 3.5 detection problem with Raspberry Pi

    Hi everyone,

    I have a Teensy 3.5 connected via USB to a Raspberry Pi. This Teensy sends data frames to the Raspberry via the serial port.

    The Teensy is recognized by the Raspberry thanks to a predefined name specified in /etc/udev/rules.d/99-usb-serial.rules (e.g. SUBSYSTEM=="tty", ATTRS{idVendor}=="16c0", ATTRS{idProduct}=="0483", ATTRS{serial}=="4514812", SYMLINK+="NAME_OF_TEENSY").

    The Raspberry runs a Python script when it starts up using the etc/rc.local file, which detects whether the Teensy in question is plugged in or not, and if so, reads and records the serial port in a .txt file.

    My problem is that for everything to work properly with a Teensy 4.0, but when I'm using a Teensy 3.5, I have to disconnect and reconnect my Teensy to the Raspberry for it to start recording frames. If the Teensy was already plugged in before the Raspberry was launched, nothing is recorded in the text file. However, if you go to /dev, the Teensy appears under the name you gave it, and the Python script is running.

    Thanks to everyone

    Here is the Python script :

    Code:
    # -*- coding: utf-8 -*-
    
    import RPi.GPIO as GPIO
    import time
    import serial
    
    from datetime import datetime
    import os
    
    dongle_removed=True
    time_before_retry=30
    
    #Verify if dongle is connected before launching
    while dongle_removed == True : 
        try:
            #Search in /dev for the name of the Teensy
            dongle=(os.popen("ls /dev | grep NAME_OF_TEENSY").read())
        except:
            pass
        #If detected
        if dongle == "NAME_OF_TEENSY\n":
            dongle_removed=False
    
            ser = serial.Serial(
                    port='/dev/NAME_OF_TEENSY',
                    baudrate = 115200,
                    parity=serial.PARITY_NONE,
                    stopbits=serial.STOPBITS_ONE,
                    bytesize=serial.EIGHTBITS,
                    timeout=5,
                    xonxoff=1
            )
        #If not detected, retry
        else:
            dongle_removed=True
            print("Dongle not detected")
            time.sleep(time_before_retry)
    
    timestr = time.strftime("%Y%m%d-%H%M%S")
    print(timestr)
    f= open("/home/record"+  timestr + ".txt" ,"w+")
    
    rec = True
    
    while True:
        time.sleep(0.1)
        try:
            dongle=(os.popen("ls /dev | grep NAME_OF_TEENSY").read())
        except:
            pass
        
        if dongle == "NAME_OF_TEENSY\n":
            if(ser.isOpen() == False):
                ser.open()
                
            #Record in .txt file
            if rec == True :
                print ("run record")
                timestr = time.strftime("%Y%m%d-%H%M%S")
                print(timestr)
                f= open("/home/record/NAME_OF_TEENSY_"+  timestr + ".txt" ,"w+")
            else :
                print ("stop record")
                f.close()
            
            #Try to read serial
            try :
                receive_ser=""
                receive_ser = ser.readline()
                print(receive_ser)
            except Exception as e:
                print("Error reading serial : ",e)
                
            else :
                dt = datetime.now().utcnow()
                time_str = str(dt.hour).zfill(2) + str(dt.minute).zfill(2) + str(dt.second).zfill(2) + '.' + str(int(float(dt.microsecond)/1000)).zfill(3)
                rec_ch = time_str + "," + receive_ser[:-3] + "," ";\r\n"
                if rec == True :
                    f.write(rec_ch + "\n")
                    f.flush()     
        else:
            print("Dongle removed")
            ser.close()
            dongle_removed=True
            print("Dongle not detected")
            time.sleep(time_before_retry)

  2. #2
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    28,473
    Quote Originally Posted by Juno View Post
    The Teensy is recognized by the Raspberry thanks to a predefined name specified in /etc/udev/rules.d/99-usb-serial.rules (e.g. SUBSYSTEM=="tty", ATTRS{idVendor}=="16c0", ATTRS{idProduct}=="0483", ATTRS{serial}=="4514812", SYMLINK+="NAME_OF_TEENSY").
    Use of "ATTRS{serial}" restricts this udev rule to 1 specific Teensy board. If you plug in a different Teensy, even if it's the same Teensy model, it will have a different serial number which causes this overly specific udev rule to no longer apply!

    I also don't quite understand how the serial number could be 4514812 (last digit of '2'). Teensy's core library always reports the serial number USB descriptor with '0' in the last digit, as a workaround for a bug in older MacOS.

  3. #3
    Junior Member
    Join Date
    May 2023
    Posts
    7
    Hi Paul, thanks for your reply,

    Sorry for the confusion, I didnít mention it but when I change the Teensy, I also change the Serial parameter with the corresponding number.

    What's more, the number I've indicated here doesn't correspond to anything, I typed it in at random because I didn't have any to hand...

    What surprises me in all this is that, whether for 3.5 or 4.0, the Teensy appears under the name I have given in /dev. But the Python script doesn't read anything from the serial port when the 3.5 is plugged into the Raspberry before power-up...

    I've also tried with another new 3.5 and there's no change.

  4. #4
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    28,473
    Quote Originally Posted by Juno View Post
    But the Python script doesn't read anything from the serial port when the 3.5 is plugged into the Raspberry before power-up...
    Before you pour a lot more time into custom python code with DIY udev rules, only for the sake of troubleshooting I'd recommend testing with Arduino IDE serial monitor using the PJRC published udev rules. Make sure everything is working the normal supported way first.

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