.TH SPLHI 10
.SH NAME
splhi, spllo, splx, islo \- enable and disable interrupts
.SH SYNOPSIS
.ta \w'\fLvoid 'u
.B
int	spllo(void)
.PP
.B
int	splhi(void)
.PP
.B
void	splx(int x)
.PP
.B
int	islo(void)
.SH DESCRIPTION
These primitives enable and disable maskable interrupts on the current
processor.
Generally, device drivers should use
.I ilock
(see
.IR lock (10)),
.IR sleep (10),
or the functions in
.IR qio (10)
to control interaction between processes and interrupt handlers.
Those routines (but not these) provide correct synchronisation on multiprocessors.
.PP
.I Spllo
enables interrupts and returns a flag representing the previous interrupt enable state.
It must not normally be called from interrupt level.
.PP
.I Splhi
disables all maskable interrupts and returns the previous interrupt enable state.
The period during which interrupts are disabled had best be short,
or real-time applications will suffer.
.PP
.I Splx
restores the interrupt enable state
state to
.IR x ,
which must be a value returned
by a previous call to
.I splhi
or
.IR spllo .
.PP
.I Islo
returns true (non-zero) if interrupts are currently enabled, and 0 otherwise.
.SH SOURCE
.B /sys/src/9/*/l.s
.SH SEE ALSO
.IR lock (10),
.IR qio (10),
.IR sleep (10),
.IR intrenable (10)