include/hw/ptimer.h

   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