osf1 man page for spl

spl(9r) 																   spl(9r)

NAME
       spl - General: Sets the processor priority to mask different levels of interrupts

SYNOPSIS
       #include <machine/cpu.h>

       int getspl(
	       void ); int splbio(
	       void ); int splclock(
	       void ); int spldevhigh(
	       void ); int splextreme(
	       void ); int splhigh(
	       void ); int splimp(
	       void ); int splnet(
	       void ); int splnone(
	       void ); int splsched(
	       void ); int splsoftclock(
	       void ); int spltty(
	       void ); int splvm(
	       void ); int splx(
	       int x );

ARGUMENTS
       Specifies a CPU priority level. This level must be a value returned by a previous call to one of the spl routines.

DESCRIPTION
       The  operating  system	supports  the naming of spl routines to indicate the associated device types. Named spl routines make it easier to
       determine which routine you should use to set the priority level for a given device type. The following table summarizes the uses  for  the
       different spl routines: Obtains the spl value.  Masks all disk and tape controller interrupts.  Masks all hardware clock interrupts.  Masks
       all device and software interrupts.  Blocks against all but halt interrupts.  Masks all interrupts except  for  realtime  devices,  machine
       checks, and halt interrupts.  Masks all LAN hardware interrupts.  Masks all network software interrupts.  Unmasks (enables) all interrupts.
       Masks all scheduling interrupts (usually the hardware clock).  Masks all software clock interrupts.  Masks all tty (terminal device) inter-
       rupts.  Masks all virtual memory clock interrupts.  Resets the CPU priority to the level specified by the argument.

NOTES
       The  binding  of  any  spl  routine  with a specific CPU priority level is highly machine dependent. With the exceptions of the splhigh and
       splnone routines, knowledge of the explicit bindings is not required to create new device drivers. You always use splhigh to mask (disable)
       all interrupts and splnone to unmask (enable) all interrupts.

RETURN VALUES
       Upon  successful  completion,  each  spl routine returns an integer value that represents the CPU priority level that existed before it was
       changed by a call to the specified spl routine.

EXAMPLE
       The following code fragment shows the use of spl routines as part of a disk strategy routine:

       int s;
	.
	.
	.  s = splbio(); /* Mask (disable) all disk interrupts */
	.
	.
	.  [Code to deal with data that can be modified by the disk interrupt code]
	.
	.
	.  splx(s); /* Restore CPU priority to what it was */

																	   spl(9r)