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 /*
  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 callback function, 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  * A transaction-based API is used for modifying ptimer state: all calls
  24  * to functions which modify ptimer state must be between matched calls to
  25  * ptimer_transaction_begin() and ptimer_transaction_commit().
  26  * When ptimer_transaction_commit() is called it will evaluate the state
  27  * of the timer after all the changes in the transaction, and call the
  28  * callback if necessary. (See the ptimer_init() documentation for the full
  29  * list of state-modifying functions and detailed semantics of the callback.)
  30  *
  31  * Forgetting to set the period/frequency (or setting it to zero) is a
  32  * bug in the QEMU device and will cause warning messages to be printed
  33  * to stderr when the guest attempts to enable the timer.
  34  */
  35
  36 /* The default ptimer policy retains backward compatibility with the legacy
  37  * timers. Custom policies are adjusting the default one. Consider providing
  38  * a correct policy for your timer.
  39  *
  40  * The rough edges of the default policy:
  41  *  - Starting to run with a period = 0 emits error message and stops the
  42  *    timer without a trigger.
  43  *
  44  *  - Setting period to 0 of the running timer emits error message and
  45  *    stops the timer without a trigger.
  46  *
  47  *  - Starting to run with counter = 0 or setting it to "0" while timer
  48  *    is running causes a trigger and reloads counter with a limit value.
  49  *    If limit = 0, ptimer emits error message and stops the timer.
  50  *
  51  *  - Counter value of the running timer is one less than the actual value.
  52  *
  53  *  - Changing period/frequency of the running timer loses time elapsed
  54  *    since the last period, effectively restarting the timer with a
  55  *    counter = counter value at the moment of change (.i.e. one less).
  56  */
  57 #define PTIMER_POLICY_DEFAULT               0
  58
  59 /* Periodic timer counter stays with "0" for a one period before wrapping
  60  * around.  */
  61 #define PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD (1 << 0)
  62
  63 /* Running periodic timer that has counter = limit = 0 would continuously
  64  * re-trigger every period.  */
  65 #define PTIMER_POLICY_CONTINUOUS_TRIGGER    (1 << 1)
  66
  67 /* Starting to run with/setting counter to "0" won't trigger immediately,
  68  * but after a one period for both oneshot and periodic modes.  */
  69 #define PTIMER_POLICY_NO_IMMEDIATE_TRIGGER  (1 << 2)
  70
  71 /* Starting to run with/setting counter to "0" won't re-load counter
  72  * immediately, but after a one period.  */
  73 #define PTIMER_POLICY_NO_IMMEDIATE_RELOAD   (1 << 3)
  74
  75 /* Make counter value of the running timer represent the actual value and
  76  * not the one less.  */
  77 #define PTIMER_POLICY_NO_COUNTER_ROUND_DOWN (1 << 4)
  78
  79 /*
  80  * Starting to run with a zero counter, or setting the counter to "0" via
  81  * ptimer_set_count() or ptimer_set_limit() will not trigger the timer
  82  * (though it will cause a reload). Only a counter decrement to "0"
  83  * will cause a trigger. Not compatible with NO_IMMEDIATE_TRIGGER;
  84  * ptimer_init() will assert() that you don't set both.
  85  */
  86 #define PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT (1 << 5)
  87
  88 /* ptimer.c */
  89 typedef struct ptimer_state ptimer_state;
  90 typedef void (*ptimer_cb)(void *opaque);
  91
  92 /**
  93  * ptimer_init - Allocate and return a new ptimer
  94  * @callback: function to call on ptimer expiry
  95  * @callback_opaque: opaque pointer passed to @callback
  96  * @policy: PTIMER_POLICY_* bits specifying behaviour
  97  *
  98  * The ptimer returned must be freed using ptimer_free().
  99  *
 100  * If a ptimer is created using this API then will use the
 101  * transaction-based API for modifying ptimer state: all calls
 102  * to functions which modify ptimer state:
 103  *  - ptimer_set_period()
 104  *  - ptimer_set_freq()
 105  *  - ptimer_set_limit()
 106  *  - ptimer_set_count()
 107  *  - ptimer_run()
 108  *  - ptimer_stop()
 109  * must be between matched calls to ptimer_transaction_begin()
 110  * and ptimer_transaction_commit(). When ptimer_transaction_commit()
 111  * is called it will evaluate the state of the timer after all the
 112  * changes in the transaction, and call the callback if necessary.
 113  *
 114  * The callback function is always called from within a transaction
 115  * begin/commit block, so the callback should not call the
 116  * ptimer_transaction_begin() function itself. If the callback changes
 117  * the ptimer state such that another ptimer expiry is triggered, then
 118  * the callback will be called a second time after the first call returns.
 119  */
 120 ptimer_state *ptimer_init(ptimer_cb callback,
 121                           void *callback_opaque,
 122                           uint8_t policy_mask);
 123
 124 /**
 125  * ptimer_free - Free a ptimer
 126  * @s: timer to free
 127  *
 128  * Free a ptimer created using ptimer_init().
 129  */
 130 void ptimer_free(ptimer_state *s);
 131
 132 /**
 133  * ptimer_transaction_begin() - Start a ptimer modification transaction
 134  *
 135  * This function must be called before making any calls to functions
 136  * which modify the ptimer's state (see the ptimer_init() documentation
 137  * for a list of these), and must always have a matched call to
 138  * ptimer_transaction_commit().
 139  * It is an error to call this function for a BH-based ptimer;
 140  * attempting to do this will trigger an assert.
 141  */
 142 void ptimer_transaction_begin(ptimer_state *s);
 143
 144 /**
 145  * ptimer_transaction_commit() - Commit a ptimer modification transaction
 146  *
 147  * This function must be called after calls to functions which modify
 148  * the ptimer's state, and completes the update of the ptimer. If the
 149  * ptimer state now means that we should trigger the timer expiry
 150  * callback, it will be called directly.
 151  */
 152 void ptimer_transaction_commit(ptimer_state *s);
 153
 154 /**
 155  * ptimer_set_period - Set counter increment interval in nanoseconds
 156  * @s: ptimer to configure
 157  * @period: period of the counter in nanoseconds
 158  *
 159  * Note that if your counter behaviour is specified as having a
 160  * particular frequency rather than a period then ptimer_set_freq()
 161  * may be more appropriate.
 162  *
 163  * This function will assert if it is called outside a
 164  * ptimer_transaction_begin/commit block.
 165  */
 166 void ptimer_set_period(ptimer_state *s, int64_t period);
 167
 168 /**
 169  * ptimer_set_period_from_clock - Set counter increment from a Clock
 170  * @s: ptimer to configure
 171  * @clk: pointer to Clock object to take period from
 172  * @divisor: value to scale the clock frequency down by
 173  *
 174  * If the ptimer is being driven from a Clock, this is the preferred
 175  * way to tell the ptimer about the period, because it avoids any
 176  * possible rounding errors that might happen if the internal
 177  * representation of the Clock period was converted to either a period
 178  * in ns or a frequency in Hz.
 179  *
 180  * If the ptimer should run at the same frequency as the clock,
 181  * pass 1 as the @divisor; if the ptimer should run at half the
 182  * frequency, pass 2, and so on.
 183  *
 184  * This function will assert if it is called outside a
 185  * ptimer_transaction_begin/commit block.
 186  */
 187 void ptimer_set_period_from_clock(ptimer_state *s, const Clock *clock,
 188                                   unsigned int divisor);
 189
 190 /**
 191  * ptimer_set_freq - Set counter frequency in Hz
 192  * @s: ptimer to configure
 193  * @freq: counter frequency in Hz
 194  *
 195  * This does the same thing as ptimer_set_period(), so you only
 196  * need to call one of them. If the counter behaviour is specified
 197  * as setting the frequency then this function is more appropriate,
 198  * because it allows specifying an effective period which is
 199  * precise to fractions of a nanosecond, avoiding rounding errors.
 200  *
 201  * This function will assert if it is called outside a
 202  * ptimer_transaction_begin/commit block.
 203  */
 204 void ptimer_set_freq(ptimer_state *s, uint32_t freq);
 205
 206 /**
 207  * ptimer_get_limit - Get the configured limit of the ptimer
 208  * @s: ptimer to query
 209  *
 210  * This function returns the current limit (reload) value
 211  * of the down-counter; that is, the value which it will be
 212  * reset to when it hits zero.
 213  *
 214  * Generally timer devices using ptimers should be able to keep
 215  * their reload register state inside the ptimer using the get
 216  * and set limit functions rather than needing to also track it
 217  * in their own state structure.
 218  */
 219 uint64_t ptimer_get_limit(ptimer_state *s);
 220
 221 /**
 222  * ptimer_set_limit - Set the limit of the ptimer
 223  * @s: ptimer
 224  * @limit: initial countdown value
 225  * @reload: if nonzero, then reset the counter to the new limit
 226  *
 227  * Set the limit value of the down-counter. The @reload flag can
 228  * be used to emulate the behaviour of timers which immediately
 229  * reload the counter when their reload register is written to.
 230  *
 231  * This function will assert if it is called outside a
 232  * ptimer_transaction_begin/commit block.
 233  */
 234 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload);
 235
 236 /**
 237  * ptimer_get_count - Get the current value of the ptimer
 238  * @s: ptimer
 239  *
 240  * Return the current value of the down-counter. This will
 241  * return the correct value whether the counter is enabled or
 242  * disabled.
 243  */
 244 uint64_t ptimer_get_count(ptimer_state *s);
 245
 246 /**
 247  * ptimer_set_count - Set the current value of the ptimer
 248  * @s: ptimer
 249  * @count: count value to set
 250  *
 251  * Set the value of the down-counter. If the counter is currently
 252  * enabled this will arrange for a timer callback at the appropriate
 253  * point in the future.
 254  *
 255  * This function will assert if it is called outside a
 256  * ptimer_transaction_begin/commit block.
 257  */
 258 void ptimer_set_count(ptimer_state *s, uint64_t count);
 259
 260 /**
 261  * ptimer_run - Start a ptimer counting
 262  * @s: ptimer
 263  * @oneshot: non-zero if this timer should only count down once
 264  *
 265  * Start a ptimer counting down; when it reaches zero the callback function
 266  * passed to ptimer_init() will be invoked.
 267  * If the @oneshot argument is zero,
 268  * the counter value will then be reloaded from the limit and it will
 269  * start counting down again. If @oneshot is non-zero, then the counter
 270  * will disable itself when it reaches zero.
 271  *
 272  * This function will assert if it is called outside a
 273  * ptimer_transaction_begin/commit block.
 274  */
 275 void ptimer_run(ptimer_state *s, int oneshot);
 276
 277 /**
 278  * ptimer_stop - Stop a ptimer counting
 279  * @s: ptimer
 280  *
 281  * Pause a timer (the count stays at its current value until ptimer_run()
 282  * is called to start it counting again).
 283  *
 284  * Note that this can cause it to "lose" time, even if it is immediately
 285  * restarted.
 286  *
 287  * This function will assert if it is called outside a
 288  * ptimer_transaction_begin/commit block.
 289  */
 290 void ptimer_stop(ptimer_state *s);
 291
 292 extern const VMStateDescription vmstate_ptimer;
 293
 294 #define VMSTATE_PTIMER(_field, _state) \
 295     VMSTATE_STRUCT_POINTER_V(_field, _state, 1, vmstate_ptimer, ptimer_state)
 296
 297 #define VMSTATE_PTIMER_ARRAY(_f, _s, _n)                                \
 298     VMSTATE_ARRAY_OF_POINTER_TO_STRUCT(_f, _s, _n, 0,                   \
 299                                        vmstate_ptimer, ptimer_state)
 300
 301 #endif