How to detect USB state changes - suspend/resume in particular?

[FeuerSturm]

Hi,

is there a callback or function that I can use to keep
track of USB state changes?
I'd need to know when the USB state changes to suspended
and resume to turn off and on attached led strips.

I've looked through the source files but didn't see anything
ready to use, any ideas?

Thanks in advance!

[defragster]

Seems some weeks/months back a status register (?) was indicated to track the connect state?

[FeuerSturm]

Seems some weeks/months back a status register (?) was indicated to track the connect state?

To be honest, I have no idea what you're trying to tell me

[defragster]

To be honest, I have no idea what you're trying to tell me

... with a search of forum there is a posting making note of a status register that changes when USB drops and returns IIRC.

[defragster]

quick search of 'usb status' found this down some dozen lines: pjrc.com/threads/70721-detecting-usb-connection-on-a-teensy-4-0

What finally worked was to check the suspend flag in the PORTSC1 register. 1 = Suspend state, 0 = not in Suspend state.

[FeuerSturm]

quick search of 'usb status' found this down some dozen lines: pjrc.com/threads/70721-detecting-usb-connection-on-a-teensy-4-0

Thank you, this is what I was looking for.
I did search various different combinations of terms, but that post didn't come up.

[FeuerSturm]

I've tried that approach and it is working unreliable for me at most.

I'm using this simple test code:

unsigned long lastCheck;

void setup()
{
	pinMode(LED_BUILTIN, OUTPUT);
}

void loop()
{
	unsigned long currentMillis = millis();
	if(currentMillis - lastCheck >= 1000)
	{
		lastCheck = currentMillis;
		if(!bitRead(USB1_PORTSC1,7))
		{
			digitalWrite(LED_BUILTIN, HIGH);
		} 
		else
		{
			digitalWrite(LED_BUILTIN, LOW);
		}
	}
}

The led does turn on, but randomly turns off for seconds and turns on again.
Am I doing something wrong?

Thanks!