SPLHI(10.2)                                           SPLHI(10.2)

          splhi, spllo, splx, islo - enable and disable interrupts

          int  spllo(void)

          int  splhi(void)

          void splx(int x)

          int  islo(void)

          These primitives enable and disable maskable interrupts on
          the current processor.  Generally, device drivers should use
          ilock (see lock(10.2)), sleep(10.2), or the functions in
          qio(10.2) to control interaction between processes and
          interrupt handlers.  Those routines (but not these) provide
          correct synchronisation on multiprocessors.

          Spllo enables interrupts and returns a flag representing the
          previous interrupt enable state.  It must not normally be
          called from interrupt level.

          Splhi disables all maskable interrupts and returns the pre-
          vious interrupt enable state.  The period during which
          interrupts are disabled had best be short, or real-time
          applications will suffer.

          Splx restores the interrupt enable state state to x, which
          must be a value returned by a previous call to splhi or

          Islo returns true (non-zero) if interrupts are currently
          enabled, and 0 otherwise.

          lock(10.2), qio(10.2), sleep(10.2), intrenable(10.2)