halt(D2)

NAME
     halt - shut down the driver when the system shuts down

SYNOPSIS
     void prefixhalt(void);

DESCRIPTION
     The halt routine if present, is called to shut down the driver when the
     system is shut down.  After the halt routine is called, no more calls
     will be made to the driver entry points.

   Return Values
     None

USAGE
     This entry point is optional.

     The device driver shouldn't assume that the interrupts are enabled.  The
     driver should make sure that no interrupts are pending from its device,
     and inform the device that no more interrupts should be generated.

   Synchronization Constraints
     User context is not available, so the driver's halt routine should not
     sleep.