Feather M4 on-board LED descriptions

Where can I read about the way the built-in infrastructure's use the on-board LEDs?

I saw a little prose buried in the CircuitPython section of a write-up about the subject board, but it doesn't seem to answer relevant questions. If I must study the source code for my answers, can someone kindly point me to the relevant modules?

As I'm struggling mightily to diagnose some serious USB/COM port problems I'm having, and post a concise thread in the Arduino forums on how the IDE handling of Windows COM ports is erratic at best, my interests surround the first handful of seconds following any kind of board reset - either by onboard button click or by the means used by the 'upload' code, and how the LEDs might tell me about the board's state and its interactions with USB 'wire'.

None of my recent application sketches manipulate any LEDs in any way.

After plugging in the USB cable for power, and seemingly always thereafter, the tiny yellow LED adjacent to the USB socket "flickers". Is that just board power, or does it tell us something about the CPU or oscillator or something else?

Several different conditions of LED illuminations on the other two onboard LEDs can be obtained with various clicks of the board reset button at various times with respect to the last reset click. All, of course, with the board still powered by the USB.

  • large LED green with fading in/out tiny red LED

  • large LED green with tiny red LED off

  • large LED red with tiny red LED off

  • It seems impossible to get the tiny red LED to fade in/out while the large LED is red, which might make perfect sense.

  • No interactions with the reset button seem capable of turning the large LED off. Only a successful upload clears that LED>

Many of the interactions with the reset button will produce somewhat expected Windows' sounds corresponding to the dropout and subsequent re-connection, but not 100% of the time. This is among the symptoms I'm investigating, and I'd like to understand what Windows is detecting at board reset and how that corresponds to the state of the LEDs.

RanHug:
I saw a little prose buried in the CircuitPython section of a write-up about the subject board, but it doesn't seem to answer relevant questions.

It might be helpful if you posted a link to that. I don't have any experience with this board, but maybe someone else here does.

RanHug:
Many of the interactions with the reset button will produce somewhat expected Windows' sounds corresponding to the dropout and subsequent re-connection, but not 100% of the time. This is among the symptoms I'm investigating, and I'd like to understand what Windows is detecting at board reset

On reset, the bootloader runs for a short time, waiting for an upload to start. On the boards with native USB like your Feather M4, that bootloader is seen by the computer as a completely different USB device than the one it sees while your application is running. You can trigger this by pressing the reset button, but the way the Arduino IDE triggers the reset to start the bootloader for an upload is to open a serial connection with the board at 1200 baud, then watch for a new port to appear, which is assumed to be the bootloader. I don't know anything about Circuit Python, so it might be that things work differently when the board is used in that way.

Thank you for that input, it gives some insight into the actual problem I'm fighting. I realize today that I posted on Arduino forums instead of Adafruit, and I apologize. To belabor the actual Arduino IDE problem I'm chasing w.r.t. COM port interactions on this thread would be off-topic, so I'll wait until I have a better grasp on those specifics before starting a new thread. Again my apologies for mis-posting.