PATH
In addition to providing access to Open Firmware config variables, the same Name Registry mechanism that saves and restores device tree properties in NVRAM has new functionality that allows communication between a Mac OS runtime driver and its corresponding Open Firmware driver. The Mac OS runtime driver sets a property in its device tree node by setting the kRegPropertyValueIsSavedToNVRAM modifier bit. This property is saved in a special Open Firmware config variable that is used by Open Firmware during boot to restore properties into the device tree. Since the properties exist when an Open Firmware driver is opened, such a property can be a message from the Mac OS runtime driver to the Open Firmware driver. The Mac OS driver will also find the property during its initialization. The new mechanism extends the size limitations for properties saved in NVRAM to 8 bytes for the name and 32 bytes for the data.