xref: /openbmc/qemu/include/hw/ptimer.h (revision 31eb7ddd)
1 /*
2  * General purpose implementation of a simple periodic countdown timer.
3  *
4  * Copyright (c) 2007 CodeSourcery.
5  *
6  * This code is licensed under the GNU LGPL.
7  */
8 #ifndef PTIMER_H
9 #define PTIMER_H
10 
11 #include "qemu/timer.h"
12 
13 /* The ptimer API implements a simple periodic countdown timer.
14  * The countdown timer has a value (which can be read and written via
15  * ptimer_get_count() and ptimer_set_count()). When it is enabled
16  * using ptimer_run(), the value will count downwards at the frequency
17  * which has been configured using ptimer_set_period() or ptimer_set_freq().
18  * When it reaches zero it will trigger a QEMU bottom half handler, and
19  * can be set to either reload itself from a specified limit value
20  * and keep counting down, or to stop (as a one-shot timer).
21  *
22  * Forgetting to set the period/frequency (or setting it to zero) is a
23  * bug in the QEMU device and will cause warning messages to be printed
24  * to stderr when the guest attempts to enable the timer.
25  */
26 
27 /* The default ptimer policy retains backward compatibility with the legacy
28  * timers. Custom policies are adjusting the default one. Consider providing
29  * a correct policy for your timer.
30  *
31  * The rough edges of the default policy:
32  *  - Starting to run with a period = 0 emits error message and stops the
33  *    timer without a trigger.
34  *
35  *  - Setting period to 0 of the running timer emits error message and
36  *    stops the timer without a trigger.
37  *
38  *  - Starting to run with counter = 0 or setting it to "0" while timer
39  *    is running causes a trigger and reloads counter with a limit value.
40  *    If limit = 0, ptimer emits error message and stops the timer.
41  *
42  *  - Counter value of the running timer is one less than the actual value.
43  *
44  *  - Changing period/frequency of the running timer loses time elapsed
45  *    since the last period, effectively restarting the timer with a
46  *    counter = counter value at the moment of change (.i.e. one less).
47  */
48 #define PTIMER_POLICY_DEFAULT               0
49 
50 /* Periodic timer counter stays with "0" for a one period before wrapping
51  * around.  */
52 #define PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD (1 << 0)
53 
54 /* Running periodic timer that has counter = limit = 0 would continuously
55  * re-trigger every period.  */
56 #define PTIMER_POLICY_CONTINUOUS_TRIGGER    (1 << 1)
57 
58 /* Starting to run with/setting counter to "0" won't trigger immediately,
59  * but after a one period for both oneshot and periodic modes.  */
60 #define PTIMER_POLICY_NO_IMMEDIATE_TRIGGER  (1 << 2)
61 
62 /* Starting to run with/setting counter to "0" won't re-load counter
63  * immediately, but after a one period.  */
64 #define PTIMER_POLICY_NO_IMMEDIATE_RELOAD   (1 << 3)
65 
66 /* Make counter value of the running timer represent the actual value and
67  * not the one less.  */
68 #define PTIMER_POLICY_NO_COUNTER_ROUND_DOWN (1 << 4)
69 
70 /*
71  * Starting to run with a zero counter, or setting the counter to "0" via
72  * ptimer_set_count() or ptimer_set_limit() will not trigger the timer
73  * (though it will cause a reload). Only a counter decrement to "0"
74  * will cause a trigger. Not compatible with NO_IMMEDIATE_TRIGGER;
75  * ptimer_init() will assert() that you don't set both.
76  */
77 #define PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT (1 << 5)
78 
79 /* ptimer.c */
80 typedef struct ptimer_state ptimer_state;
81 typedef void (*ptimer_cb)(void *opaque);
82 
83 /**
84  * ptimer_init - Allocate and return a new ptimer
85  * @bh: QEMU bottom half which is run on timer expiry
86  * @policy: PTIMER_POLICY_* bits specifying behaviour
87  *
88  * The ptimer returned must be freed using ptimer_free().
89  * The ptimer takes ownership of @bh and will delete it
90  * when the ptimer is eventually freed.
91  */
92 ptimer_state *ptimer_init(QEMUBH *bh, uint8_t policy_mask);
93 
94 /**
95  * ptimer_free - Free a ptimer
96  * @s: timer to free
97  *
98  * Free a ptimer created using ptimer_init() (including
99  * deleting the bottom half which it is using).
100  */
101 void ptimer_free(ptimer_state *s);
102 
103 /**
104  * ptimer_set_period - Set counter increment interval in nanoseconds
105  * @s: ptimer to configure
106  * @period: period of the counter in nanoseconds
107  *
108  * Note that if your counter behaviour is specified as having a
109  * particular frequency rather than a period then ptimer_set_freq()
110  * may be more appropriate.
111  */
112 void ptimer_set_period(ptimer_state *s, int64_t period);
113 
114 /**
115  * ptimer_set_freq - Set counter frequency in Hz
116  * @s: ptimer to configure
117  * @freq: counter frequency in Hz
118  *
119  * This does the same thing as ptimer_set_period(), so you only
120  * need to call one of them. If the counter behaviour is specified
121  * as setting the frequency then this function is more appropriate,
122  * because it allows specifying an effective period which is
123  * precise to fractions of a nanosecond, avoiding rounding errors.
124  */
125 void ptimer_set_freq(ptimer_state *s, uint32_t freq);
126 
127 /**
128  * ptimer_get_limit - Get the configured limit of the ptimer
129  * @s: ptimer to query
130  *
131  * This function returns the current limit (reload) value
132  * of the down-counter; that is, the value which it will be
133  * reset to when it hits zero.
134  *
135  * Generally timer devices using ptimers should be able to keep
136  * their reload register state inside the ptimer using the get
137  * and set limit functions rather than needing to also track it
138  * in their own state structure.
139  */
140 uint64_t ptimer_get_limit(ptimer_state *s);
141 
142 /**
143  * ptimer_set_limit - Set the limit of the ptimer
144  * @s: ptimer
145  * @limit: initial countdown value
146  * @reload: if nonzero, then reset the counter to the new limit
147  *
148  * Set the limit value of the down-counter. The @reload flag can
149  * be used to emulate the behaviour of timers which immediately
150  * reload the counter when their reload register is written to.
151  */
152 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload);
153 
154 /**
155  * ptimer_get_count - Get the current value of the ptimer
156  * @s: ptimer
157  *
158  * Return the current value of the down-counter. This will
159  * return the correct value whether the counter is enabled or
160  * disabled.
161  */
162 uint64_t ptimer_get_count(ptimer_state *s);
163 
164 /**
165  * ptimer_set_count - Set the current value of the ptimer
166  * @s: ptimer
167  * @count: count value to set
168  *
169  * Set the value of the down-counter. If the counter is currently
170  * enabled this will arrange for a timer callback at the appropriate
171  * point in the future.
172  */
173 void ptimer_set_count(ptimer_state *s, uint64_t count);
174 
175 /**
176  * ptimer_run - Start a ptimer counting
177  * @s: ptimer
178  * @oneshot: non-zero if this timer should only count down once
179  *
180  * Start a ptimer counting down; when it reaches zero the bottom half
181  * passed to ptimer_init() will be invoked. If the @oneshot argument is zero,
182  * the counter value will then be reloaded from the limit and it will
183  * start counting down again. If @oneshot is non-zero, then the counter
184  * will disable itself when it reaches zero.
185  */
186 void ptimer_run(ptimer_state *s, int oneshot);
187 
188 /**
189  * ptimer_stop - Stop a ptimer counting
190  * @s: ptimer
191  *
192  * Pause a timer (the count stays at its current value until ptimer_run()
193  * is called to start it counting again).
194  *
195  * Note that this can cause it to "lose" time, even if it is immediately
196  * restarted.
197  */
198 void ptimer_stop(ptimer_state *s);
199 
200 extern const VMStateDescription vmstate_ptimer;
201 
202 #define VMSTATE_PTIMER(_field, _state) \
203     VMSTATE_STRUCT_POINTER_V(_field, _state, 1, vmstate_ptimer, ptimer_state)
204 
205 #define VMSTATE_PTIMER_ARRAY(_f, _s, _n)                                \
206     VMSTATE_ARRAY_OF_POINTER_TO_STRUCT(_f, _s, _n, 0,                   \
207                                        vmstate_ptimer, ptimer_state)
208 
209 #endif
210