Low power mode with USB wake up

Document created by Fang Li Employee on Jun 30, 2016
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The Kinetis family has abundant low power mode. Customers may confused to figure out the different way to wake up from the low power mode.

 

1)  In VLPR, VLPW:  the NVIC remains sensitive to interrupts, so any interrupt will be serviced.

2)  In Stop, VLPS:  the device can be waked up by USB wake up interrupt only.
3)  In LLS, VLLSx:  the device won't be able to wake up from any USB source.
4)  LLWU is used to wake up, so customer would able to wake up from any of the available LLWU wake up sources.


As for t
he USB module, there has two different interrupts for a USB resume event. One asynchronous to be able to wake from a low power mode, which is triggered by change in the state of the USB lines. The other is synchronous and is triggered only after 2.5 us of detecting a K state (D+ = 0, D- = 1, for Full Speed). The application is responsible to transition to the low power mode whenever it requires it, and for this purpose it must check the device state as reported by the USB stack. When a suspend condition is detected in the bus, the SLEEP interrupt triggers and the stack changes its state to suspend; then the application will transition to the low power mode. When this SLEEP interrupt occurs, the asynchronous wake interrupt is enabled, and is disabled when it is triggered (this is required by the module to clear the interrupt). In normal conditions, the synchronous resume interrupt or the reset interrupt will be triggered afterwards, causing the stack to transition its state to other than suspend. The application can then know that communication is active again and will avoid entering the low power mode again.

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