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45 .Nd manipulate interrupt priorities
60 .Fn splsoftclock "void"
64 .Fn splstatclock "void"
70 .Fn splx "intrmask_t ipl"
74 function family sets the interrupt priority
77 This prevents interrupt handlers of the blocked priority level from
78 being run. This is used in the
80 part of a driver (the part that runs on behalf of the user process) to
81 examine or modify data areas that might be examined or modified by
84 Each driver that uses interrupts is normally assigned to an interrupt
85 priority group by a keyword in its config line.
87 .Bd -literal -offset indent
88 device foo0 at isa? port 0x0815 irq 12 tty
91 assigns interrupt 12 to the
93 priority group. The system automatically arranges for interrupts in
96 group to be called at a priority >=
102 sets the interrupt priority to an absolute value. The intent is that
103 the value returned by the other functions should be saved in a local
104 variable, and later passed to
106 in order to restore the previous priority.
110 lowers the priority to a value where all interrupt handlers are
111 unblocked, but ASTs (asynchronous system traps) remain blocked until
112 the system is about to return to user mode.
114 The traditional assignment of the various device drivers to the
115 interrupt priority groups can be roughly classified as:
118 All network interface drivers.
122 (i.e., disk and the like) drivers.
124 Basically, all non-network communications devices, but effectively
125 used for all drivers that are neither network nor disks.
132 return the previous priority value.
134 This is a typical example demonstrating the usage:
147 struct foo_softc *sc;
152 if (!(sc->flags & FOO_READY)) {
153 /* Not ready, must sleep on resource. */
154 sc->flags |= FOO_ASLEEP;
155 error = tsleep(sc, PZERO, "foordy", 0);
156 sc->flags &= ~FOO_ASLEEP;
158 sc->flags &= ~FOO_READY;
167 struct foo_softc *sc;
170 sc->flags |= FOO_READY;
171 if (sc->flags & FOO_ASLEEP)
172 /* Somebody was waiting for us, awake him. */
178 Note that the interrupt handler should
180 reduce the priority level. It is automatically called as it had
181 raised the interrupt priority to its own level, i.e. further interrupts
182 of the same group are being blocked.
184 The interrupt priority levels appeared in a very early version of
185 Unix. They have been traditionally known by number instead of by
186 names, and were inclusive up to higher priority levels (i.e., priority
187 5 has been blocking everything up to level 5). This is no longer the
192 for them is still reflected in the letter
194 of the respective functions and variables, although they are not
195 really levels anymore, but rather different (partially inclusive)
196 sets of functions to be blocked during some periods of the life of
197 the system. The historical number scheme can be considered as a
198 simple linearly ordered set of interrupt priority groups.
200 This man page was written by