38.6.3.8 Remote Wakeup

The controller Host mode enters the Suspend state when the USBHS_HSTCTRL.SOFE bit is written to zero. No more “Start of Frame” is sent on the USB bus and the USB device enters the Suspend state 3 ms later.

The device awakes the host by sending an Upstream Resume (Remote Wakeup feature). When the host controller detects a non-idle state on the USB bus, it sets the Host Wakeup interrupt (USBHS_HSTISR.HWUPI) bit. If the non-idle bus state corresponds to an Upstream Resume (K state), the Upstream Resume Received Interrupt (USBHS_HSTISR.RXRSMI) bit is set. The user has to generate a Downstream Resume within 1 ms and for at least 20 ms by writing a one to the Send USB Resume (USBHS_HSTCTRL.RESUME) bit. It is mandatory to write a one to USBHS_HSTCTRL.SOFE before writing a one to USBHS_HSTCTRL.RESUME to enter the Ready state, otherwise USBHS_HSTCTRL.RESUME has no effect.