STLink not reliably working on several NUCLEO-L476RG boards

[Clark Sann]

I have 5 NUCLEO-L476RG development boards. I purchased them in the last few months. Two of them are only a couple weeks old and have not been used except for the test below.

The problem is that when I plug into the board, the LD1 and LD3 LEDs often start blinking. When this happens it is not possible to connect to the board and do any program loading or debugging. LD1 is on when STLink is communicating. LD3 is power from the STLink.

I have tried a variety of cables and that does not make any difference. I have also used CubeProgrammer to show the firmware version of each board. The firmware versions are V2J37M26 and V2J30M19. Some of the devices with the newer firmware blink. All the devices with the older firmware blink. On all the devices that blink, unplugging and replugging in the USB will eventually allow me to connect although some devices are so unreliable that I may have to plug in 10 or more times to get the device to work.

What would cause both of these LEDs to blink when power is applied? Is the STLink rebooting?

Is there anything I can do to make these boards work properly?

[KnarfB]

Never seen this before. If you can read the firmware version, you can try upgrading to the lastest using CubeProgrammer. I you haven't already, try also plugging to a different host.

[Uwe Bonnes]

Expect bad usb cables, rooten USB hubs, broken connectors etc, Be sure to have no shields etc connected. Compare jumper and resistor jumper settings. Carefully read the stlink manuals about the meaning of the blinking leds. Blinking can mean e.g. bootloader active or overcurrent or failing enumeration.

[Clark Sann]

Thank you both for your help. I can have updated firmware. @Uwe Bonnes​ i didn’t know there were STLink manuals. I will try to find them. I have discovered I had an GPIO configured as an output that was connected to the blue button on the NUCLEO board. That may have caused an over current. And I now think one of my programming cables does not always work. If you can easily send me a link to the STLink manual that discusses this problem, I would appreciate it.

[ChahinezC]

Hello @Clark Sann​,

I recommend you checking the cables you are using, the jumpers settings, the ST-LINK driver installation and the firmware upgrade.

Please refer to the ST-link Technical note, and the STM32 Nucleo-64 boards User Manual.

The 6.2 section of the user manual will provide you with information regarding the embedded ST-LINK on the STM32 Nucleo-64 boards and the required settings, as for the 6.4 section, it will help you check the LED blinking status.

Chahinez.

[Clark Sann]

@ChahinezC​ Thank you for this information. As I mentioned in my post, when this problem occurs, both LD1 and LD3 LEDs start blinking. LD3 is the 5V power from the ST-link. Why would that blink? Is the ST-link resetting itself and constantly setting and resetting PWR_ENn from the ST-Link? If so, what would cause this?

[Tesla DeLorean]

TBH I don't spend a lot of time pondering what the lights do or don't mean in any context. I don't recall any on-board ST-LINK failures on 100's of boards, over 10 years, that I've used these things. I've run into people who blown boards, with high voltages, and floating grounds.

Try disconnecting the the SWDIO/SWCLK pins to the target (should be a pair of jumpers).

Does this materially change the behaviour of the LEDs?

Do you put the L4 into a Low Power mode?

Do you do anything with PB3, PA13, PA14 ?

You have anything hung of the primary board?