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 /* ptimer.c */
  73 typedef struct ptimer_state ptimer_state;
  74 typedef void (*ptimer_cb)(void *opaque);
  75
  76 /**
  77  * ptimer_init - Allocate and return a new ptimer
  78  * @bh: QEMU bottom half which is run on timer expiry
  79  * @policy: PTIMER_POLICY_* bits specifying behaviour
  80  *
  81  * The ptimer returned must be freed using ptimer_free().
  82  * The ptimer takes ownership of @bh and will delete it
  83  * when the ptimer is eventually freed.
  84  */
  85 ptimer_state *ptimer_init(QEMUBH *bh, uint8_t policy_mask);
  86
  87 /**
  88  * ptimer_free - Free a ptimer
  89  * @s: timer to free
  90  *
  91  * Free a ptimer created using ptimer_init() (including
  92  * deleting the bottom half which it is using).
  93  */
  94 void ptimer_free(ptimer_state *s);
  95
  96 /**
  97  * ptimer_set_period - Set counter increment interval in nanoseconds
  98  * @s: ptimer to configure
  99  * @period: period of the counter in nanoseconds
 100  *
 101  * Note that if your counter behaviour is specified as having a
 102  * particular frequency rather than a period then ptimer_set_freq()
 103  * may be more appropriate.
 104  */
 105 void ptimer_set_period(ptimer_state *s, int64_t period);
 106
 107 /**
 108  * ptimer_set_freq - Set counter frequency in Hz
 109  * @s: ptimer to configure
 110  * @freq: counter frequency in Hz
 111  *
 112  * This does the same thing as ptimer_set_period(), so you only
 113  * need to call one of them. If the counter behaviour is specified
 114  * as setting the frequency then this function is more appropriate,
 115  * because it allows specifying an effective period which is
 116  * precise to fractions of a nanosecond, avoiding rounding errors.
 117  */
 118 void ptimer_set_freq(ptimer_state *s, uint32_t freq);
 119
 120 /**
 121  * ptimer_get_limit - Get the configured limit of the ptimer
 122  * @s: ptimer to query
 123  *
 124  * This function returns the current limit (reload) value
 125  * of the down-counter; that is, the value which it will be
 126  * reset to when it hits zero.
 127  *
 128  * Generally timer devices using ptimers should be able to keep
 129  * their reload register state inside the ptimer using the get
 130  * and set limit functions rather than needing to also track it
 131  * in their own state structure.
 132  */
 133 uint64_t ptimer_get_limit(ptimer_state *s);
 134
 135 /**
 136  * ptimer_set_limit - Set the limit of the ptimer
 137  * @s: ptimer
 138  * @limit: initial countdown value
 139  * @reload: if nonzero, then reset the counter to the new limit
 140  *
 141  * Set the limit value of the down-counter. The @reload flag can
 142  * be used to emulate the behaviour of timers which immediately
 143  * reload the counter when their reload register is written to.
 144  */
 145 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload);
 146
 147 /**
 148  * ptimer_get_count - Get the current value of the ptimer
 149  * @s: ptimer
 150  *
 151  * Return the current value of the down-counter. This will
 152  * return the correct value whether the counter is enabled or
 153  * disabled.
 154  */
 155 uint64_t ptimer_get_count(ptimer_state *s);
 156
 157 /**
 158  * ptimer_set_count - Set the current value of the ptimer
 159  * @s: ptimer
 160  * @count: count value to set
 161  *
 162  * Set the value of the down-counter. If the counter is currently
 163  * enabled this will arrange for a timer callback at the appropriate
 164  * point in the future.
 165  */
 166 void ptimer_set_count(ptimer_state *s, uint64_t count);
 167
 168 /**
 169  * ptimer_run - Start a ptimer counting
 170  * @s: ptimer
 171  * @oneshot: non-zero if this timer should only count down once
 172  *
 173  * Start a ptimer counting down; when it reaches zero the bottom half
 174  * passed to ptimer_init() will be invoked. If the @oneshot argument is zero,
 175  * the counter value will then be reloaded from the limit and it will
 176  * start counting down again. If @oneshot is non-zero, then the counter
 177  * will disable itself when it reaches zero.
 178  */
 179 void ptimer_run(ptimer_state *s, int oneshot);
 180
 181 /**
 182  * ptimer_stop - Stop a ptimer counting
 183  * @s: ptimer
 184  *
 185  * Pause a timer (the count stays at its current value until ptimer_run()
 186  * is called to start it counting again).
 187  *
 188  * Note that this can cause it to "lose" time, even if it is immediately
 189  * restarted.
 190  */
 191 void ptimer_stop(ptimer_state *s);
 192
 193 extern const VMStateDescription vmstate_ptimer;
 194
 195 #define VMSTATE_PTIMER(_field, _state) \
 196     VMSTATE_STRUCT_POINTER_V(_field, _state, 1, vmstate_ptimer, ptimer_state)
 197
 198 #define VMSTATE_PTIMER_ARRAY(_f, _s, _n)                                \
 199     VMSTATE_ARRAY_OF_POINTER_TO_STRUCT(_f, _s, _n, 0,                   \
 200                                        vmstate_ptimer, ptimer_state)
 201
 202 #endif