11.1.1 Designing Device Drivers with DriverControl Routines

Most NT drivers of DMA devices must have an AdapterControl routine:

• Every NT driver of a DMA device that is connected to a system DMA controller must have an AdapterControl routine.

• Any NT driver of a busmaster DMA device must have an AdapterControl routine unless that driver’s designer decides to use the system’s common-buffer DMA support exclusively.

At the driver writer’s discretion, an NT device driver can have a ControllerControl routine in order to synchronize its operations to similar devices through a single physical controller or adapter.

The I/O Manager defines a single type (DRIVER_CONTROL) for AdapterControl and ControllerControl routines because each is called indirectly, usually from the StartIo routine, when a driver needs to synchronize access to a physical device that might already be busy:

• When a driver calls IoAllocateAdapterChannel, its AdapterControl routine is run immediately if the system DMA controller or busmaster adapter is available for a DMA operation. Otherwise, the AdapterControl routine is queued until the DMA controller or busmaster adapter is free.

• When a driver calls IoAllocateController, its ControllerControl routine is run immediately if the hardware represented by the controller object is available for an I/O operation. Otherwise, the ControllerControl routine is queued until the controller is free.

For a ControllerControl routine, the input PVOID MapRegisterBase, shown in the DRIVER_CONTROL declaration, is a system-reserved value.