.TH altclk_in() "" "" "Internal Kernel Routine"
.PC "Install polling function"
\fBint altclk_in(\fIhz, fn\^\fB)\fR
\fBint \fIhz\^\fB, (*\fIfn\^\fB)();\fR
.PP
.B altclk_in()
increases the system clock rate from the value set by manifest constant
.B HZ
(at present, 100 Hertz) to
.IR hz .
.I fn
points to the function to be called whenever the clock interrupt occurs.
.I hz
must be an integral multiple of
.BR HZ ;
therefore, the rate of clock interrupts will be increased by a
factor of \fIhz\fB/HZ\fR.
.I fn
is an \fBint\fR-valued function that must return
zero every \fIhz\fB/HZ\fR'th time it is called, nonzero the rest of the time.
The zero value returned from
.I fn
tells the \*(CO system's clock routine to do its usual processing.
.PP
.B altclk_in()
returns zero if it completes normally;
if argument
.I hz
is less than
.B HZ
or not an integral multiple of
.BR HZ ,
this function does nothing and returns \-1.
.SH "See Also"
.B
altclk_out(),
internal kernel routines
.R
