2 .\" Copyright (c) 2011 Alexander Motin <mav@FreeBSD.org>
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32 .Nd kernel event timers subsystem
38 typedef int et_start_t(struct eventtimer *et,
39 struct bintime *first, struct bintime *period);
40 typedef int et_stop_t(struct eventtimer *et);
41 typedef void et_event_cb_t(struct eventtimer *et, void *arg);
42 typedef int et_deregister_cb_t(struct eventtimer *et, void *arg);
45 SLIST_ENTRY(eventtimer) et_all;
48 #define ET_FLAGS_PERIODIC 1
49 #define ET_FLAGS_ONESHOT 2
50 #define ET_FLAGS_PERCPU 4
51 #define ET_FLAGS_C3STOP 8
52 #define ET_FLAGS_POW2DIV 16
55 uint64_t et_frequency;
56 struct bintime et_min_period;
57 struct bintime et_max_period;
60 et_event_cb_t *et_event_cb;
61 et_deregister_cb_t *et_deregister_cb;
64 struct sysctl_oid *et_sysctl;
68 .Fn et_register "struct eventtimer *et"
70 .Fn et_deregister "struct eventtimer *et"
73 .Ft struct eventtimer *
74 .Fn et_find "const char *name" "int check" "int want"
76 .Fn et_init "struct eventtimer *et" "et_event_cb_t *event" "et_deregister_cb_t *deregister" "void *arg"
78 .Fn et_start "struct eventtimer *et" "struct bintime *first" "struct bintime *period"
80 .Fn et_stop "struct eventtimer *et"
82 .Fn et_ban "struct eventtimer *et"
84 .Fn et_free "struct eventtimer *et"
86 Event timers are responsible for generating interrupts at specified time
87 or periodically, to run different time-based events.
88 Subsystem consists of three main parts:
89 .Bl -tag -width "Consumers"
91 Manage hardware to generate requested time events.
93 .Pa sys/kern/kern_clocksource.c
94 uses event timers to supply kernel with
101 .Pa sys/sys/timeet.h ,
102 .Pa sys/kern/kern_et.c
103 provide APIs for event timer drivers and consumers.
106 Driver API is built around eventtimer structure.
107 To register its functionality driver allocates that structure and calls
109 Driver should fill following fields there:
112 Unique name of the event timer for management purposes.
114 Set of flags, describing timer capabilities:
115 .Bl -tag -width "ET_FLAGS_PERIODIC" -compact
116 .It ET_FLAGS_PERIODIC
117 Periodic mode supported.
119 One-shot mode supported.
123 Timer may stop in CPU sleep state.
125 Timer supports only 2^n divisors.
128 Abstract value to certify whether this timecounter is better than the others.
129 Higher value means better.
131 Timer oscillator's base frequency, if applicable and known.
132 Used by consumers to predict set of possible frequencies that could be
133 obtained by dividing it.
134 Should be zero if not applicable or unknown.
135 .It Va et_min_period , et_max_period
136 Minimal and maximal reliably programmable time periods.
138 Driver's timer start function pointer.
140 Driver's timer stop function pointer.
142 Driver's private data storage.
145 After the event timer functionality is registered, it is controlled via
151 method is called to start the specified event timer.
152 The last two arguments are used to specify time when events should be
155 argument specifies time period before the first event generated.
156 In periodic mode NULL value specifies that first period is equal to the
160 argument specifies the time period between following events for the
162 The NULL value there specifies the one-shot mode.
163 At least one of these two arguments should be not NULL.
164 When event time arrive, driver should call
166 callback function, passing
168 as the second argument.
170 method is called to stop the specified event timer.
171 For the per-CPU event timers
175 methods control timers associated with the current CPU.
177 Driver may deregister its functionality by calling
181 allows consumer to find available event timer, optionally matching specific
182 name and/or capability flags.
183 Consumer may read returned eventtimer structure, but should not modify it.
184 When wanted event timer is found,
186 should be called for it, submitting
190 callbacks functions, and the opaque argument
192 That argument will be passed as argument to the callbacks.
193 Event callback function will be called on scheduled time events.
194 It is called from the hardware interrupt context, so no sleep is permitted
196 Deregister callback function may be called to report consumer that the event
197 timer functionality is no longer available.
198 On this call, consumer should stop using event timer before the return.
200 After the timer is found and initialized, it can be controlled via
204 The arguments are the same as described in driver API.
205 Per-CPU event timers can be controlled only from specific CPUs.
208 allows consumer to mark event timer as broken via clearing both one-shot and
209 periodic capability flags, if it was somehow detected.
213 It releases the event timer for other consumers use.
218 macros should be used to manage
225 calls to serialize access to the list of the registered event timers and the
231 calls should be serialized in consumer's internal way to avoid concurrent
232 timer hardware access.
236 .An Alexander Motin Aq mav@FreeBSD.org