Active Power Management

This section describes the functions you need to use to implement the active power management scheme.

Do the following work in the attach(9E) entry point for your driver:

1. Call usb_create_pm_components(9F).

2. Optionally call usb_handle_remote_wakeup(9F) with USB_REMOTE_WAKEUP_ENABLE as the second argument to enable a remote wakeup on the device.

3. Call pm_busy_component(9F).

4. Call pm_raise_power(9F) to take power to the USB_DEV_OS_FULL_PWR level.

5. Communicate with the device to initialize the device.

6. Call pm_idle_component(9F).

Do the following work in the detach(9E) entry point for your driver:

1. Call pm_busy_component(9F).

2. Call pm_raise_power(9F) to take power to the USB_DEV_OS_FULL_PWR level.

3. If you called the usb_handle_remote_wakeup(9F) function in your attach(9E) entry point, call usb_handle_remote_wakeup(9F) here with USB_REMOTE_WAKEUP_DISABLE as the second argument.

4. Communicate with the device to cleanly shut down the device.

5. Call pm_lower_power(9F) to take power to the USB_DEV_OS_PWR_OFF level.

   This is the only time a client driver calls pm_lower_power(9F).

6. Call pm_idle_component(9F).

When a driver thread wants to start I/O to the device, that thread does the following tasks:

1. Call pm_busy_component(9F).

2. Call pm_raise_power(9F) to take power to the USB_DEV_OS_FULL_PWR level.

3. Begin the I/O transfer.

The driver calls pm_idle_component(9F) when the driver receives notice that an I/O transfer has completed.

In the power(9E) entry point for your driver, check whether the power level to which you are transitioning is valid. You might also need to account for different threads calling into power(9E) at the same time.

The power(9E) routine might be called to take the device to the USB_DEV_OS_PWR_OFF state if the device has been idle for some time or the system is shutting down. This state corresponds to the PWRED_DWN state shown in Figure 20–4. If the device is going to the USB_DEV_OS_PWR_OFF state, do the following work in your power(9E) routine:

1. Put all open pipes into the idle state. For example, stop polling on the interrupt pipe.

2. Save any device or driver context that needs to be saved.

   The port to which the device is connected is suspended after the call to power(9E) completes.

The power(9E) routine might be called to power on the device when either a device-initiated remote wakeup or a system-initiated wakeup is received. Wakeup notices occur after the device has been powered down due to extended idle time or system suspend. If the device is going to the USB_DEV_OS_PWR_1 state or above, do the following work in your power(9E) routine:

1. Restore any needed device and driver context.

2. Restart activity on the pipe that is appropriate to the specified power level. For example, start polling on the interrupt pipe.

If the port to which the device is connected was previously suspended, that port is resumed before power(9E) is called.