Minimal USB event detection

[ryanlush]

I have a bootloader and application running on a K20. When the processor boots it initializes the USB peripheral as a CDC bulk device and then waits 1500ms to see if it enumerates. If it doesn't enumerate I set a flag to boot the application and forget all about USB until the user cycles power.

This worked great until we buried the device in a vehicles engine compartment and connected it directly to the battery. Now its not so easy to cycle power.

So I'm looking for a minimal way to sense the bus is active from the application and reset the processor. I had hoped that I could...

enable the USB clock in the SCG

enable USB interrupts in the NVIC

enable USB in the USB0_CTL

enable the AVBUSEN interrupt in the USB0_OTGICR

and reset the processor in the ISR. However, I'm not getting any interrupts.

Am I on the right path? Is there a better way to do this? The goal here is to either fix it in software or come up with a good argument for a new board revision. I really think this is doable in software without setting up the USB peripheral as a bulk device

[bobpaddock]

Try using the Start of Frame IRQ bit to check for an active connection.

[Hui_Ma]

Hi,

First of all, sorry for the later reply.

If K20 as USB CDC device will be always connected to PC or not?

How to check if the USB device enumerated successfully or not, which need to check the USB stack state.

If just to check if the USB device attached to PC, customer can use the USB module interrupt.

Thank you for the attention.

Have a great day,
Ma Hui

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