Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 13 of 13

Thread: T4.0 Hangs, Small LED flashes twice then Pauses...continuously doing that sequence

  1. #1
    Senior Member
    Join Date
    Jan 2019
    Posts
    129

    T4.0 Hangs, Small LED flashes twice then Pauses...continuously doing that sequence

    T4.0 Hangs, Small LED flashes twice then Pauses...continuously doing that sequence.

    Is this something that is know, is this an error code of some sort?

  2. #2
    Senior Member+ defragster's Avatar
    Join Date
    Feb 2015
    Posts
    16,364
    The diagnostic RED LED flashes are noted on this page: 2 Blinks = NXP JTAG Not Responding

    The note for that is:
    No communication is working! The 2 likely causes for this problem are improper power startup sequence, or a problem with any of these connections between the MKL02 and IMXRT chip
    How is the Teensy being powered? Standard USB or external supply?

    Had it worked before and been programmed from new?

  3. #3
    Senior Member
    Join Date
    Jan 2019
    Posts
    129
    Powered externally - there is a diode in the line.
    the sketch would be running for hours, or minutes, or seconds and then does it.
    It is likely to do it on USB cable removal.


    Project involves SPI communication.

    update: device hangs and then pressing reset button it start blinking twice. Trying to see if it only blinks during the attempted reset after hang.

  4. #4
    Senior Member+ defragster's Avatar
    Join Date
    Feb 2015
    Posts
    16,364
    Note: The T_4.0 does not have a RESET button.

    The Button on the T_4.0 puts the Teensy into Program mode.

  5. #5
    Senior Member
    Join Date
    Jan 2019
    Posts
    129
    OK. So it's going into 2 blink mode by itself, no program button

  6. #6
    Senior Member+ defragster's Avatar
    Join Date
    Feb 2015
    Posts
    16,364
    Pushing the button would have a different RED LED response.

    The 2 Blink suggests it restarted (after power loss?) - and the (external?) power was not suitable in current supply and rise time.

    The 2 Blinks is on External or removing USB and going to external?

    Is it always fine on USB power? How is the External power isolated from being present at the same time as the USB power.

  7. #7
    Senior Member
    Join Date
    Jan 2019
    Posts
    129
    The freeze happens either on USB, or EXT or on both.
    the power is isolated by cutting the line on the board and adding a diode.
    Noticed now that at 600Mhz it freezes, on 396 Mhz the freeze is yet to be seen.

    Gonna do some more ABABABA tests and see.

  8. #8
    Senior Member+ KurtE's Avatar
    Join Date
    Jan 2014
    Posts
    10,974
    Maybe we should back up some here, and get back to basics.

    That is, which LED is blinking? RED or Orange?

    Click image for larger version. 

Name:	Screenshot.jpg 
Views:	3 
Size:	27.9 KB 
ID:	29075

    If Red one near USB port than the number of blinks might mean the stuff mentioned.

    If the Orange one near Pins 13 and 14 than that is completely different. That is saying Pin 13 is being set HIGH or LOW...

    Like maybe the code is running something like:
    Code:
    void setup() {
      // initialize digital pin LED_BUILTIN as an output.
      pinMode(LED_BUILTIN, OUTPUT);
    }
    
    // the loop function runs over and over again forever
    void loop() {
      digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
      delay(250);                       // wait for a second
      digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
      delay(250);                       // wait for a second
      digitalWrite(LED_BUILTIN, HIGH);    // turn the LED off by making the voltage LOW
      delay(250);                       // wait for a second
      digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
      delay(1000);                       // wait for a second
    }
    This could be anything! For example, sometimes I have put in code like this in some function to let me know it failed. And maybe I put in different blink patterns depending on which failure.

    But so far in this thread I am not sure I have seen anything about what is hooked up to the T4? What code are you running or the like? So sort of hard to give any suggestions on what to check.

  9. #9
    Senior Member
    Join Date
    Jan 2019
    Posts
    129
    Not pin 13 but the smaller debug led

    I have a spi lcd connected.

    EDIT:

    yup, def not loving the 600MHZ.

    I'm going to add 22ohm resistor on the SPI lines at the teensy for the next circuit design and see how that works.
    Last edited by donperryjm; 07-31-2022 at 07:14 PM.

  10. #10
    Senior Member+ KurtE's Avatar
    Join Date
    Jan 2014
    Posts
    10,974
    Sorry, again I am probably not much help here, other than ask questions and maybe throw a dart or two. And maybe it might help to localize down the issue.

    Is this a new T4? Or have you had it for a while? Wondering which Voltage Regulator, it has on it? There was a recent thread about one of the newer VR not booting at lower voltage. I think it needed to be about 4v.

    Which display are you using? How is it hooked up? More particular what are the power connections? Like is it connected to +5v or 3.3v? Reason asking is for example some displays like RA8875 can draw more current than the onboard 3.3v VR could handle, so when I played with them, I ordered them with their own VR on the board. Or on my own board, I might include separate VR for the display on other peripherals.

    Wondering if there is something in the code that is triggering this? Something like, maybe some code overwrites some critical memory locations or the like. I would tend to do things like instrument the code with a bunch of either Serial.prints() and/or digitalWriteFast/digitalToggleFast in different portions of the code and hook up Logic Analyzer or the like to see if anything maybe helps point to if something went wrong in the program.

    Again, I know not much help!

    Good luck

  11. #11
    Senior Member
    Join Date
    Jan 2019
    Posts
    129
    Thanks. Your help is appreciated.
    It's a newer t4 lockable.
    Since lowring the cpu frequency it has yet to freeze.

  12. #12
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    26,810
    Does the problem change if you remove the diode and connect the power with just a wire? Or maybe use a DC voltmeter to check the actual power supply voltage arriving at the VIN pin?

    An issue was recently discovered where Teensy 4.0 would not power up with less than about 4.0 to 4.1, due to a component substitution on the 3.3V regulator and a 100K resistor on the regulator enable pin. Changing the resistor to 470K allows for startup down to as low as 3.2 volts. Starting with the next production batch which begins to arrive next week, all Teensy 4.0 will be made with the 470K resistor.

    Of course, this is just a blind guess. The "freeze" you're seeing may be something completely different.

  13. #13
    Senior Member
    Join Date
    Jan 2019
    Posts
    129
    Oh. The diode voltage drop. Maybe the voltage req was why it wasn't stable at 600 mhz but OK at 396?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •