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 /* 37 * The 'legacy' ptimer policy retains backward compatibility with the 38 * traditional ptimer behaviour from before policy flags were introduced. 39 * It has several weird behaviours which don't match typical hardware 40 * timer behaviour. For a new device using ptimers, you should not 41 * use PTIMER_POLICY_LEGACY, but instead check the actual behaviour 42 * that you need and specify the right set of policy flags to get that. 43 * 44 * If you are overhauling an existing device that uses PTIMER_POLICY_LEGACY 45 * and are in a position to check or test the real hardware behaviour, 46 * consider updating it to specify the right policy flags. 47 * 48 * The rough edges of the default policy: 49 * - Starting to run with a period = 0 emits error message and stops the 50 * timer without a trigger. 51 * 52 * - Setting period to 0 of the running timer emits error message and 53 * stops the timer without a trigger. 54 * 55 * - Starting to run with counter = 0 or setting it to "0" while timer 56 * is running causes a trigger and reloads counter with a limit value. 57 * If limit = 0, ptimer emits error message and stops the timer. 58 * 59 * - Counter value of the running timer is one less than the actual value. 60 * 61 * - Changing period/frequency of the running timer loses time elapsed 62 * since the last period, effectively restarting the timer with a 63 * counter = counter value at the moment of change (.i.e. one less). 64 */ 65 #define PTIMER_POLICY_LEGACY 0 66 67 /* Periodic timer counter stays with "0" for a one period before wrapping 68 * around. */ 69 #define PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD (1 << 0) 70 71 /* Running periodic timer that has counter = limit = 0 would continuously 72 * re-trigger every period. */ 73 #define PTIMER_POLICY_CONTINUOUS_TRIGGER (1 << 1) 74 75 /* Starting to run with/setting counter to "0" won't trigger immediately, 76 * but after a one period for both oneshot and periodic modes. */ 77 #define PTIMER_POLICY_NO_IMMEDIATE_TRIGGER (1 << 2) 78 79 /* Starting to run with/setting counter to "0" won't re-load counter 80 * immediately, but after a one period. */ 81 #define PTIMER_POLICY_NO_IMMEDIATE_RELOAD (1 << 3) 82 83 /* Make counter value of the running timer represent the actual value and 84 * not the one less. */ 85 #define PTIMER_POLICY_NO_COUNTER_ROUND_DOWN (1 << 4) 86 87 /* 88 * Starting to run with a zero counter, or setting the counter to "0" via 89 * ptimer_set_count() or ptimer_set_limit() will not trigger the timer 90 * (though it will cause a reload). Only a counter decrement to "0" 91 * will cause a trigger. Not compatible with NO_IMMEDIATE_TRIGGER; 92 * ptimer_init() will assert() that you don't set both. 93 */ 94 #define PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT (1 << 5) 95 96 /* ptimer.c */ 97 typedef struct ptimer_state ptimer_state; 98 typedef void (*ptimer_cb)(void *opaque); 99 100 /** 101 * ptimer_init - Allocate and return a new ptimer 102 * @callback: function to call on ptimer expiry 103 * @callback_opaque: opaque pointer passed to @callback 104 * @policy: PTIMER_POLICY_* bits specifying behaviour 105 * 106 * The ptimer returned must be freed using ptimer_free(). 107 * 108 * If a ptimer is created using this API then will use the 109 * transaction-based API for modifying ptimer state: all calls 110 * to functions which modify ptimer state: 111 * - ptimer_set_period() 112 * - ptimer_set_freq() 113 * - ptimer_set_limit() 114 * - ptimer_set_count() 115 * - ptimer_run() 116 * - ptimer_stop() 117 * must be between matched calls to ptimer_transaction_begin() 118 * and ptimer_transaction_commit(). When ptimer_transaction_commit() 119 * is called it will evaluate the state of the timer after all the 120 * changes in the transaction, and call the callback if necessary. 121 * 122 * The callback function is always called from within a transaction 123 * begin/commit block, so the callback should not call the 124 * ptimer_transaction_begin() function itself. If the callback changes 125 * the ptimer state such that another ptimer expiry is triggered, then 126 * the callback will be called a second time after the first call returns. 127 */ 128 ptimer_state *ptimer_init(ptimer_cb callback, 129 void *callback_opaque, 130 uint8_t policy_mask); 131 132 /** 133 * ptimer_free - Free a ptimer 134 * @s: timer to free 135 * 136 * Free a ptimer created using ptimer_init(). 137 */ 138 void ptimer_free(ptimer_state *s); 139 140 /** 141 * ptimer_transaction_begin() - Start a ptimer modification transaction 142 * 143 * This function must be called before making any calls to functions 144 * which modify the ptimer's state (see the ptimer_init() documentation 145 * for a list of these), and must always have a matched call to 146 * ptimer_transaction_commit(). 147 * It is an error to call this function for a BH-based ptimer; 148 * attempting to do this will trigger an assert. 149 */ 150 void ptimer_transaction_begin(ptimer_state *s); 151 152 /** 153 * ptimer_transaction_commit() - Commit a ptimer modification transaction 154 * 155 * This function must be called after calls to functions which modify 156 * the ptimer's state, and completes the update of the ptimer. If the 157 * ptimer state now means that we should trigger the timer expiry 158 * callback, it will be called directly. 159 */ 160 void ptimer_transaction_commit(ptimer_state *s); 161 162 /** 163 * ptimer_set_period - Set counter increment interval in nanoseconds 164 * @s: ptimer to configure 165 * @period: period of the counter in nanoseconds 166 * 167 * Note that if your counter behaviour is specified as having a 168 * particular frequency rather than a period then ptimer_set_freq() 169 * may be more appropriate. 170 * 171 * This function will assert if it is called outside a 172 * ptimer_transaction_begin/commit block. 173 */ 174 void ptimer_set_period(ptimer_state *s, int64_t period); 175 176 /** 177 * ptimer_set_period_from_clock - Set counter increment from a Clock 178 * @s: ptimer to configure 179 * @clk: pointer to Clock object to take period from 180 * @divisor: value to scale the clock frequency down by 181 * 182 * If the ptimer is being driven from a Clock, this is the preferred 183 * way to tell the ptimer about the period, because it avoids any 184 * possible rounding errors that might happen if the internal 185 * representation of the Clock period was converted to either a period 186 * in ns or a frequency in Hz. 187 * 188 * If the ptimer should run at the same frequency as the clock, 189 * pass 1 as the @divisor; if the ptimer should run at half the 190 * frequency, pass 2, and so on. 191 * 192 * This function will assert if it is called outside a 193 * ptimer_transaction_begin/commit block. 194 */ 195 void ptimer_set_period_from_clock(ptimer_state *s, const Clock *clock, 196 unsigned int divisor); 197 198 /** 199 * ptimer_set_freq - Set counter frequency in Hz 200 * @s: ptimer to configure 201 * @freq: counter frequency in Hz 202 * 203 * This does the same thing as ptimer_set_period(), so you only 204 * need to call one of them. If the counter behaviour is specified 205 * as setting the frequency then this function is more appropriate, 206 * because it allows specifying an effective period which is 207 * precise to fractions of a nanosecond, avoiding rounding errors. 208 * 209 * This function will assert if it is called outside a 210 * ptimer_transaction_begin/commit block. 211 */ 212 void ptimer_set_freq(ptimer_state *s, uint32_t freq); 213 214 /** 215 * ptimer_get_limit - Get the configured limit of the ptimer 216 * @s: ptimer to query 217 * 218 * This function returns the current limit (reload) value 219 * of the down-counter; that is, the value which it will be 220 * reset to when it hits zero. 221 * 222 * Generally timer devices using ptimers should be able to keep 223 * their reload register state inside the ptimer using the get 224 * and set limit functions rather than needing to also track it 225 * in their own state structure. 226 */ 227 uint64_t ptimer_get_limit(ptimer_state *s); 228 229 /** 230 * ptimer_set_limit - Set the limit of the ptimer 231 * @s: ptimer 232 * @limit: initial countdown value 233 * @reload: if nonzero, then reset the counter to the new limit 234 * 235 * Set the limit value of the down-counter. The @reload flag can 236 * be used to emulate the behaviour of timers which immediately 237 * reload the counter when their reload register is written to. 238 * 239 * This function will assert if it is called outside a 240 * ptimer_transaction_begin/commit block. 241 */ 242 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload); 243 244 /** 245 * ptimer_get_count - Get the current value of the ptimer 246 * @s: ptimer 247 * 248 * Return the current value of the down-counter. This will 249 * return the correct value whether the counter is enabled or 250 * disabled. 251 */ 252 uint64_t ptimer_get_count(ptimer_state *s); 253 254 /** 255 * ptimer_set_count - Set the current value of the ptimer 256 * @s: ptimer 257 * @count: count value to set 258 * 259 * Set the value of the down-counter. If the counter is currently 260 * enabled this will arrange for a timer callback at the appropriate 261 * point in the future. 262 * 263 * This function will assert if it is called outside a 264 * ptimer_transaction_begin/commit block. 265 */ 266 void ptimer_set_count(ptimer_state *s, uint64_t count); 267 268 /** 269 * ptimer_run - Start a ptimer counting 270 * @s: ptimer 271 * @oneshot: non-zero if this timer should only count down once 272 * 273 * Start a ptimer counting down; when it reaches zero the callback function 274 * passed to ptimer_init() will be invoked. 275 * If the @oneshot argument is zero, 276 * the counter value will then be reloaded from the limit and it will 277 * start counting down again. If @oneshot is non-zero, then the counter 278 * will disable itself when it reaches zero. 279 * 280 * This function will assert if it is called outside a 281 * ptimer_transaction_begin/commit block. 282 */ 283 void ptimer_run(ptimer_state *s, int oneshot); 284 285 /** 286 * ptimer_stop - Stop a ptimer counting 287 * @s: ptimer 288 * 289 * Pause a timer (the count stays at its current value until ptimer_run() 290 * is called to start it counting again). 291 * 292 * Note that this can cause it to "lose" time, even if it is immediately 293 * restarted. 294 * 295 * This function will assert if it is called outside a 296 * ptimer_transaction_begin/commit block. 297 */ 298 void ptimer_stop(ptimer_state *s); 299 300 extern const VMStateDescription vmstate_ptimer; 301 302 #define VMSTATE_PTIMER(_field, _state) \ 303 VMSTATE_STRUCT_POINTER_V(_field, _state, 1, vmstate_ptimer, ptimer_state) 304 305 #define VMSTATE_PTIMER_ARRAY(_f, _s, _n) \ 306 VMSTATE_ARRAY_OF_POINTER_TO_STRUCT(_f, _s, _n, 0, \ 307 vmstate_ptimer, ptimer_state) 308 309 #endif 310