SPLHI(9)                                                 SPLHI(9)

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

     SYNOPSIS
          int  spllo(void)

          int  splhi(void)

          void splx(int x)

          int  islo(void)

     DESCRIPTION
          These primitives enable and disable maskable interrupts on
          the current processor.  Generally, device drivers should use
          ilock (see lock(9)), sleep(9), or the functions in qio(9) to
          control interaction between processes and interrupt han-
          dlers.  Those routines (but not these) provide correct syn-
          chronisation 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 to x, which must be
          a value returned by a previous call to splhi or spllo.

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

     SOURCE
          /sys/src/9/*/l.s

     SEE ALSO
          lock(9), qio(9), sleep(9), intrenable(9)