STM32H743 Micropython V1.23 Coroutine Error: 'SingletonGenerator' object has no attribute 'exc' after long runtime #18360

chiyu-Charon · 2025-11-03T04:06:08Z

chiyu-Charon
Nov 3, 2025

I'm using an STM32H743 with firmware I compiled myself, based on Micropython V1.23. After running normally for a long time, all of a sudden, all my coroutines start throwing an error. The error message is: "'SingletonGenerator' object has no attribute 'exc'". The error occurs in the asyncio/core.py file.

# "Yield" once, then raise StopIteration
class SingletonGenerator:
    def __init__(self):
        self.state = None
        self.exc = StopIteration()

    def __iter__(self):
        return self

    def __next__(self):
        if not hasattr(self, "exc") or self.exc is None:
            self.exc = StopIteration()
        if self.state is not None:
            _task_queue.push(cur_task, self.state)
            self.state = None
            return None
        else:
            self.exc.__traceback__ = None
            raise self.exc

Since I can't save the REPL print in real-time when the device is running and connected to the USB, when I connect the USB later, the buffer only has the content shown in the image. Apologies, my device doesn't allow me to export a screenshot, so I can only capture it with my phone.

Does anyone know what might cause this error? Thanks

peterhinch · 2025-11-03T12:29:52Z

peterhinch
Nov 3, 2025
Collaborator

Given that the error is occurring in asyncio.core.py we can probably rule out a bug - the strong likelihood is RAM fragmentation. I have seen similar "missing attribute" errors in these circumstances. In large applications expected to run for long durations it can help to run gc.collect() periodically. Also check out the official docs on optimisation.

2 replies

chiyu-Charon Nov 7, 2025
Author

Thanks! I have a dedicated coroutine that calls gc.collect every 5 seconds or so and prints the free memory. The output shows that there’s always about 50MB of free memory (I’ve set up an external RAM for extra memory).
Could it be that the gc.collect is being called too frequently?
Would it be more appropriate to switch to automatic cleanup using gc.threshold?

peterhinch Nov 7, 2025
Collaborator

Calling gc every 5s is fine. In asynchronous applications this easily done and is the approach I use. If you have 50MB of free RAM it seems unlikely that fragmentation is the problem unless you're creating and destroying large (>1MB) objects.

I'm stumped for answers here, except to re-iterate that missing attributes do suggest a RAM issue. Could there be a hardware problem with your extra RAM?

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

MicroPython

STM32H743 Micropython V1.23 Coroutine Error: 'SingletonGenerator' object has no attribute 'exc' after long runtime #18360

Uh oh!

{{title}}

Uh oh!

Uh oh!

{{editor}}'s edit

{{editor}}'s edit

Uh oh!

Replies: 1 comment 2 replies

Uh oh!

{{title}}

Uh oh!

Uh oh!

{{title}}

Uh oh!

Uh oh!

{{title}}

Uh oh!

Select a reply

Uh oh!

MicroPython

STM32H743 Micropython V1.23 Coroutine Error: 'SingletonGenerator' object has no attribute 'exc' after long runtime #18360

Uh oh!

Uh oh!

chiyu-Charon Nov 3, 2025

Replies: 1 comment · 2 replies

Uh oh!

peterhinch Nov 3, 2025 Collaborator

Uh oh!

chiyu-Charon Nov 7, 2025 Author

Uh oh!

peterhinch Nov 7, 2025 Collaborator

chiyu-Charon
Nov 3, 2025

Replies: 1 comment 2 replies

peterhinch
Nov 3, 2025
Collaborator

chiyu-Charon Nov 7, 2025
Author

peterhinch Nov 7, 2025
Collaborator