From 8fd1ca9d49979ab32bf3316f1847a055a99e6d77 Mon Sep 17 00:00:00 2001 From: joerg Date: Fri, 4 Oct 1996 21:22:49 +0000 Subject: Add a man page describing the interrupt priority `levels'. Comments by: bde Lousy MCI network link :(, my commit message for the Makefile has been botched. --- share/man/man9/spl.9 | 199 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 199 insertions(+) create mode 100644 share/man/man9/spl.9 (limited to 'share/man') diff --git a/share/man/man9/spl.9 b/share/man/man9/spl.9 new file mode 100644 index 0000000..dbf5e57 --- /dev/null +++ b/share/man/man9/spl.9 @@ -0,0 +1,199 @@ +.\" +.\" Copyright (c) 1996 Joerg Wunsch +.\" +.\" All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR +.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES +.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. +.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, +.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT +.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF +.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. +.\" +.\" $Id$ +.\" " +.Dd July 21, 1996 +.Os +.Dt SPL 9 +.Sh NAME +.Nm splbio, +.Nm splclock, +.Nm splhigh, +.Nm splimp, +.Nm splnet, +.Nm splsoftclock, +.Nm splsofttty, +.Nm splstatclock, +.Nm spltty, +.Nm splvm, +.Nm spl0, +.Nm splx +.Nd manipulate interrupt priorities +.Sh SYNOPSIS +.Fd #include +.Fd #include +.Ft int +.Fn splbio "void" +.Ft int +.Fn splclock "void" +.Ft int +.Fn splhigh "void" +.Ft int +.Fn splimp "void" +.Ft int +.Fn splnet "void" +.Ft int +.Fn splsoftclock "void" +.Ft int +.Fn splsofttty "void" +.Ft int +.Fn splstatclock "void" +.Ft int +.Fn spltty "void" +.Ft void +.Fn spl0 "void" +.Ft void +.Fn splx "int ipl" +.Sh DESCRIPTION +The +.Fn spl +function family sets the interrupt priority +.Dq level +of the CPU. +This prevents interrupt handlers of the blocked priority level from +being run. This is used in the +.Dq synchronous +part of a driver (the part that runs on behalf of the user process) to +examine or modify data areas that might be examined or modified by +interrupt handlers. +.Pp +Each driver that uses interrupts is normally assigned to an interrupt +priority group by a keyword in its config line. +For example: +.Bd -literal -offset indent +device foo0 at isa? port 0x0815 irq 12 tty vector foointr +.Ed +.Pp +assigns interrupt 12 to the +.Dq tty +priority group. The system automatically arranges for interrupts in +the +.Em xxx +group to be called at a priority >= +.Ns spl Ns Em xxx +\&(). +.Pp +The function +.Fn splx +sets the interrupt priority to an absolute value. The intent is that +the value returned by the other functions should be saved in a local +variable, and later passed to +.Fn splx +in order to restore the previous priority. +.Pp +The function +.Fn spl0 +lowers the priority to a value where all interrupt handlers are +unblocked, but ASTs (asynchronous system traps) remain blocked until +the system is about to return to user mode. +.Pp +The traditional assignment of the various device drivers to the +interrupt priority groups can be roughly classified as: +.Bl -tag -width Fn splnet +.It Fn splnet +All network interface drivers. +.It Fn splbio +All +.Em buffered IO +(i.e., disk and the like) drivers. +.It Fn spltty +Basically, all non-network communications devices, but effectively +used for all drivers that are neither network nor disks. +.El +.Sh RETURN VALUES +All functions except +.Fn splx +and +.Fn spl0 +return the previous priority value. +.Sh EXAMPLES +This is a typical example demonstrating the usage: +.Bd -literal +struct foo_softc { + ... + int flags; +#define FOO_ASLEEP 1 +#define FOO_READY 2 + +} foo_softc[NFOO]; + +int +foowrite(...) +{ + struct foo_softc *sc; + int s, error; + + ... + s = spltty(); + if (!(sc->flags & FOO_READY)) { + /* Not ready, must sleep on resource. */ + sc->flags |= FOO_ASLEEP; + error = tsleep(sc, PZERO, "foordy", 0); + sc->flags &= ~FOO_ASLEEP; + } + sc->flags &= ~FOO_READY; + splx(s); + + ... +} + +void +foointr(...) +{ + struct foo_softc *sc; + + ... + sc->flags |= FOO_READY; + if (sc->flags & FOO_ASLEEP) + /* Somebody was waiting for us, awake him. */ + wakeup(sc); + ... +} + +.Ed +Note that the interrupt handler should +.Em never +reduce the priority level. It is automatically called as it had +raised the interrupt priority to its own level, i.e. further interrupts +of the same group are being blocked. +.Sh HISTORY +The interrupt priority levels appeared in a very early version of +Unix. They have been traditionally known by number instead of by +names, and were inclusive up to higher priority levels (i.e., priority +5 has been blocking everything up to level 5). This is no longer the +case in FreeBSD. The traditional name +.Ql level +for them is still reflected in the letter +.Ql l +of the respective functions and variables, although they are not +really levels anymore, but rather different (partially inclusive) +sets of functions to be blocked during some periods of the life of +the system. The historical number scheme can be considered as a +simple linearly ordered set of interrupt priority groups. +.Sh AUTHORS +This man page was written by +.ie t J\(:org Wunsch. +.el Joerg Wunsch. -- cgit v1.1