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