harvey/sys/man/9/intrenable

.TH INTRENABLE 9
.SH NAME
intrenable, intrdisable \- enable (disable) an interrupt handler
.SH SYNOPSIS
.ta \w'\fLvoid* 'u
.B
void intrenable(int v, void (*f)(Ureg*, void*), void* a, int tbdf, char *name)
.PP
.B
void intrdisable(int v, void (*f)(Ureg*, void*), void* a, int tbdf, char *name)
.SH DESCRIPTION
.I Intrenable
registers
.I f
to be called by the kernel's interrupt controller driver each time
an interrupt denoted by
.I v
occurs, and unmasks the corresponding interrupt in the interrupt controller.
The encoding of
.I v
is platform-dependent; it is often an interrupt vector number, but
can be more complex.
.I Tbdf
is a platform-dependent value that might further qualify
.IR v .
It might for instance
denote the type of bus, bus instance, device number and function
(following the PCI device indexing scheme), hence its name,
but can have platform-dependent meaning.
.I Name
is a string that should uniquely identify the corresponding device (eg, \f5"uart0"\fP);
again it is usually platform-dependent.
.I Intrenable
supports sharing of interrupt levels when the hardware does.
.PP
Almost invariably
.I f
is a function defined in a device driver to carry out the device-specific work associated with a given interrupt.
The pointer
.I a
is passed to
.IR f ;
typically it points to the driver's data for a given device or controller.
It also passes
.I f
a
.B Ureg*
value that
contains the registers saved by the interrupt handler (the
contents are platform specific;
see the platform's include file
.BR "ureg.h" ).
.PP
.I F
is invoked by underlying code in the kernel that is invoked directly from the hardware vectors.
It is therefore not running in any process (see
.IR kproc (9);
indeed, on many platforms
the current process pointer
.RB ( up )
will be nil.
There are many restrictions on kernel functions running outside a process, but a fundamental one is that
they must not
.IR sleep (9),
although they often call
.B wakeup
to signal the occurrence of an event associated with the interrupt.
.IR Qio (9)
and other manual pages note which functions are safe for
.I f
to call.
.PP
The interrupt controller driver does whatever is
required to acknowledge or dismiss the interrupt signal in the interrupt controller,
before calling
.IR f ,
for edge-triggered interrupts,
and after calling
.I f
for level-triggered ones.
.I F
is responsible for deal with the cause of the interrupt in the device, including any
acknowledgement required in the device, before it returns.
.PP
.I Intrdisable
removes any registration previously made by
.I intrenable
with matching parameters, and if no other
interrupt is active on
.IR v ,
it masks the interrupt in the controller.
Device drivers that are not dynamically configured tend to call
.I intrenable
during reset or initialisation (see
.IR dev (9)),
but can call it at any appropriate time, and
instead of calling
.I intrdisable
they can simply enable or disable interrupts in the device as required.
.SH SOURCE
.B /sys/src/9/*/trap.c
.SH SEE ALSO
.IR malloc (9),
.IR qio (9),
.IR sleep (9),
.IR splhi (9)