The following figure describes the USBHS Host mode main states.
After a hardware reset, the USBHS Host mode is in the Reset state.
When the USBHS is enabled (USBHS_CTRL.USBE = 1) in Host mode (USBHS_CTRL.UIMOD = 0), it goes to the Idle state. In this state, the controller waits for a device connection with a minimal power consumption. The USB pad should be in the Idle state. Once a device is connected, the USBHS enters the Ready state, which does not require the USB clock to be activated.
The controller enters the Suspend state when the USB bus is in a “Suspend” state, i.e., when the Host mode does not generate the “Start of Frame (SOF)”. In this state, the USB consumption is minimal. The Host mode exits the Suspend state when starting to generate the SOF over the USB line.