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