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_with_bh() 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_with_bh - 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_with_bh(QEMUBH *bh, uint8_t policy_mask);
  93
  94 /**
  95  * ptimer_init - Allocate and return a new ptimer
  96  * @callback: function to call on ptimer expiry
  97  * @callback_opaque: opaque pointer passed to @callback
  98  * @policy: PTIMER_POLICY_* bits specifying behaviour
  99  *
 100  * The ptimer returned must be freed using ptimer_free().
 101  *
 102  * If a ptimer is created using this API then will use the
 103  * transaction-based API for modifying ptimer state: all calls
 104  * to functions which modify ptimer state:
 105  *  - ptimer_set_period()
 106  *  - ptimer_set_freq()
 107  *  - ptimer_set_limit()
 108  *  - ptimer_set_count()
 109  *  - ptimer_run()
 110  *  - ptimer_stop()
 111  * must be between matched calls to ptimer_transaction_begin()
 112  * and ptimer_transaction_commit(). When ptimer_transaction_commit()
 113  * is called it will evaluate the state of the timer after all the
 114  * changes in the transaction, and call the callback if necessary.
 115  *
 116  * The callback function is always called from within a transaction
 117  * begin/commit block, so the callback should not call the
 118  * ptimer_transaction_begin() function itself. If the callback changes
 119  * the ptimer state such that another ptimer expiry is triggered, then
 120  * the callback will be called a second time after the first call returns.
 121  */
 122 ptimer_state *ptimer_init(ptimer_cb callback,
 123                           void *callback_opaque,
 124                           uint8_t policy_mask);
 125
 126 /**
 127  * ptimer_free - Free a ptimer
 128  * @s: timer to free
 129  *
 130  * Free a ptimer created using ptimer_init_with_bh() (including
 131  * deleting the bottom half which it is using).
 132  */
 133 void ptimer_free(ptimer_state *s);
 134
 135 /**
 136  * ptimer_transaction_begin() - Start a ptimer modification transaction
 137  *
 138  * This function must be called before making any calls to functions
 139  * which modify the ptimer's state (see the ptimer_init() documentation
 140  * for a list of these), and must always have a matched call to
 141  * ptimer_transaction_commit().
 142  * It is an error to call this function for a BH-based ptimer;
 143  * attempting to do this will trigger an assert.
 144  */
 145 void ptimer_transaction_begin(ptimer_state *s);
 146
 147 /**
 148  * ptimer_transaction_commit() - Commit a ptimer modification transaction
 149  *
 150  * This function must be called after calls to functions which modify
 151  * the ptimer's state, and completes the update of the ptimer. If the
 152  * ptimer state now means that we should trigger the timer expiry
 153  * callback, it will be called directly.
 154  */
 155 void ptimer_transaction_commit(ptimer_state *s);
 156
 157 /**
 158  * ptimer_set_period - Set counter increment interval in nanoseconds
 159  * @s: ptimer to configure
 160  * @period: period of the counter in nanoseconds
 161  *
 162  * Note that if your counter behaviour is specified as having a
 163  * particular frequency rather than a period then ptimer_set_freq()
 164  * may be more appropriate.
 165  *
 166  * This function will assert if it is called outside a
 167  * ptimer_transaction_begin/commit block, unless this is a bottom-half ptimer.
 168  */
 169 void ptimer_set_period(ptimer_state *s, int64_t period);
 170
 171 /**
 172  * ptimer_set_freq - Set counter frequency in Hz
 173  * @s: ptimer to configure
 174  * @freq: counter frequency in Hz
 175  *
 176  * This does the same thing as ptimer_set_period(), so you only
 177  * need to call one of them. If the counter behaviour is specified
 178  * as setting the frequency then this function is more appropriate,
 179  * because it allows specifying an effective period which is
 180  * precise to fractions of a nanosecond, avoiding rounding errors.
 181  *
 182  * This function will assert if it is called outside a
 183  * ptimer_transaction_begin/commit block, unless this is a bottom-half ptimer.
 184  */
 185 void ptimer_set_freq(ptimer_state *s, uint32_t freq);
 186
 187 /**
 188  * ptimer_get_limit - Get the configured limit of the ptimer
 189  * @s: ptimer to query
 190  *
 191  * This function returns the current limit (reload) value
 192  * of the down-counter; that is, the value which it will be
 193  * reset to when it hits zero.
 194  *
 195  * Generally timer devices using ptimers should be able to keep
 196  * their reload register state inside the ptimer using the get
 197  * and set limit functions rather than needing to also track it
 198  * in their own state structure.
 199  */
 200 uint64_t ptimer_get_limit(ptimer_state *s);
 201
 202 /**
 203  * ptimer_set_limit - Set the limit of the ptimer
 204  * @s: ptimer
 205  * @limit: initial countdown value
 206  * @reload: if nonzero, then reset the counter to the new limit
 207  *
 208  * Set the limit value of the down-counter. The @reload flag can
 209  * be used to emulate the behaviour of timers which immediately
 210  * reload the counter when their reload register is written to.
 211  *
 212  * This function will assert if it is called outside a
 213  * ptimer_transaction_begin/commit block, unless this is a bottom-half ptimer.
 214  */
 215 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload);
 216
 217 /**
 218  * ptimer_get_count - Get the current value of the ptimer
 219  * @s: ptimer
 220  *
 221  * Return the current value of the down-counter. This will
 222  * return the correct value whether the counter is enabled or
 223  * disabled.
 224  */
 225 uint64_t ptimer_get_count(ptimer_state *s);
 226
 227 /**
 228  * ptimer_set_count - Set the current value of the ptimer
 229  * @s: ptimer
 230  * @count: count value to set
 231  *
 232  * Set the value of the down-counter. If the counter is currently
 233  * enabled this will arrange for a timer callback at the appropriate
 234  * point in the future.
 235  *
 236  * This function will assert if it is called outside a
 237  * ptimer_transaction_begin/commit block, unless this is a bottom-half ptimer.
 238  */
 239 void ptimer_set_count(ptimer_state *s, uint64_t count);
 240
 241 /**
 242  * ptimer_run - Start a ptimer counting
 243  * @s: ptimer
 244  * @oneshot: non-zero if this timer should only count down once
 245  *
 246  * Start a ptimer counting down; when it reaches zero the bottom half
 247  * passed to ptimer_init_with_bh() will be invoked.
 248  * If the @oneshot argument is zero,
 249  * the counter value will then be reloaded from the limit and it will
 250  * start counting down again. If @oneshot is non-zero, then the counter
 251  * will disable itself when it reaches zero.
 252  *
 253  * This function will assert if it is called outside a
 254  * ptimer_transaction_begin/commit block, unless this is a bottom-half ptimer.
 255  */
 256 void ptimer_run(ptimer_state *s, int oneshot);
 257
 258 /**
 259  * ptimer_stop - Stop a ptimer counting
 260  * @s: ptimer
 261  *
 262  * Pause a timer (the count stays at its current value until ptimer_run()
 263  * is called to start it counting again).
 264  *
 265  * Note that this can cause it to "lose" time, even if it is immediately
 266  * restarted.
 267  *
 268  * This function will assert if it is called outside a
 269  * ptimer_transaction_begin/commit block, unless this is a bottom-half ptimer.
 270  */
 271 void ptimer_stop(ptimer_state *s);
 272
 273 extern const VMStateDescription vmstate_ptimer;
 274
 275 #define VMSTATE_PTIMER(_field, _state) \
 276     VMSTATE_STRUCT_POINTER_V(_field, _state, 1, vmstate_ptimer, ptimer_state)
 277
 278 #define VMSTATE_PTIMER_ARRAY(_f, _s, _n)                                \
 279     VMSTATE_ARRAY_OF_POINTER_TO_STRUCT(_f, _s, _n, 0,                   \
 280                                        vmstate_ptimer, ptimer_state)
 281
 282 #endif