310 lines
12 KiB
C
310 lines
12 KiB
C
/*
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* General purpose implementation of a simple periodic countdown timer.
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*
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* Copyright (c) 2007 CodeSourcery.
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*
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* This code is licensed under the GNU LGPL.
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*/
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#ifndef PTIMER_H
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#define PTIMER_H
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#include "qemu/timer.h"
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/*
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* The ptimer API implements a simple periodic countdown timer.
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* The countdown timer has a value (which can be read and written via
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* ptimer_get_count() and ptimer_set_count()). When it is enabled
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* using ptimer_run(), the value will count downwards at the frequency
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* which has been configured using ptimer_set_period() or ptimer_set_freq().
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* When it reaches zero it will trigger a callback function, and
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* can be set to either reload itself from a specified limit value
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* and keep counting down, or to stop (as a one-shot timer).
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*
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* A transaction-based API is used for modifying ptimer state: all calls
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* to functions which modify ptimer state must be between matched calls to
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* ptimer_transaction_begin() and ptimer_transaction_commit().
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* When ptimer_transaction_commit() is called it will evaluate the state
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* of the timer after all the changes in the transaction, and call the
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* callback if necessary. (See the ptimer_init() documentation for the full
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* list of state-modifying functions and detailed semantics of the callback.)
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*
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* Forgetting to set the period/frequency (or setting it to zero) is a
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* bug in the QEMU device and will cause warning messages to be printed
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* to stderr when the guest attempts to enable the timer.
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*/
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/*
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* The 'legacy' ptimer policy retains backward compatibility with the
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* traditional ptimer behaviour from before policy flags were introduced.
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* It has several weird behaviours which don't match typical hardware
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* timer behaviour. For a new device using ptimers, you should not
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* use PTIMER_POLICY_LEGACY, but instead check the actual behaviour
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* that you need and specify the right set of policy flags to get that.
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*
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* If you are overhauling an existing device that uses PTIMER_POLICY_LEGACY
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* and are in a position to check or test the real hardware behaviour,
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* consider updating it to specify the right policy flags.
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*
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* The rough edges of the default policy:
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* - Starting to run with a period = 0 emits error message and stops the
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* timer without a trigger.
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*
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* - Setting period to 0 of the running timer emits error message and
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* stops the timer without a trigger.
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*
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* - Starting to run with counter = 0 or setting it to "0" while timer
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* is running causes a trigger and reloads counter with a limit value.
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* If limit = 0, ptimer emits error message and stops the timer.
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*
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* - Counter value of the running timer is one less than the actual value.
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*
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* - Changing period/frequency of the running timer loses time elapsed
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* since the last period, effectively restarting the timer with a
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* counter = counter value at the moment of change (.i.e. one less).
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*/
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#define PTIMER_POLICY_LEGACY 0
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/* Periodic timer counter stays with "0" for a one period before wrapping
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* around. */
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#define PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD (1 << 0)
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/* Running periodic timer that has counter = limit = 0 would continuously
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* re-trigger every period. */
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#define PTIMER_POLICY_CONTINUOUS_TRIGGER (1 << 1)
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/* Starting to run with/setting counter to "0" won't trigger immediately,
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* but after a one period for both oneshot and periodic modes. */
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#define PTIMER_POLICY_NO_IMMEDIATE_TRIGGER (1 << 2)
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/* Starting to run with/setting counter to "0" won't re-load counter
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* immediately, but after a one period. */
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#define PTIMER_POLICY_NO_IMMEDIATE_RELOAD (1 << 3)
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/* Make counter value of the running timer represent the actual value and
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* not the one less. */
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#define PTIMER_POLICY_NO_COUNTER_ROUND_DOWN (1 << 4)
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/*
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* Starting to run with a zero counter, or setting the counter to "0" via
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* ptimer_set_count() or ptimer_set_limit() will not trigger the timer
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* (though it will cause a reload). Only a counter decrement to "0"
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* will cause a trigger. Not compatible with NO_IMMEDIATE_TRIGGER;
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* ptimer_init() will assert() that you don't set both.
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*/
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#define PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT (1 << 5)
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/* ptimer.c */
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typedef struct ptimer_state ptimer_state;
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typedef void (*ptimer_cb)(void *opaque);
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/**
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* ptimer_init - Allocate and return a new ptimer
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* @callback: function to call on ptimer expiry
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* @callback_opaque: opaque pointer passed to @callback
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* @policy: PTIMER_POLICY_* bits specifying behaviour
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*
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* The ptimer returned must be freed using ptimer_free().
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*
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* If a ptimer is created using this API then will use the
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* transaction-based API for modifying ptimer state: all calls
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* to functions which modify ptimer state:
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* - ptimer_set_period()
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* - ptimer_set_freq()
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* - ptimer_set_limit()
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* - ptimer_set_count()
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* - ptimer_run()
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* - ptimer_stop()
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* must be between matched calls to ptimer_transaction_begin()
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* and ptimer_transaction_commit(). When ptimer_transaction_commit()
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* is called it will evaluate the state of the timer after all the
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* changes in the transaction, and call the callback if necessary.
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*
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* The callback function is always called from within a transaction
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* begin/commit block, so the callback should not call the
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* ptimer_transaction_begin() function itself. If the callback changes
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* the ptimer state such that another ptimer expiry is triggered, then
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* the callback will be called a second time after the first call returns.
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*/
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ptimer_state *ptimer_init(ptimer_cb callback,
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void *callback_opaque,
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uint8_t policy_mask);
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/**
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* ptimer_free - Free a ptimer
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* @s: timer to free
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*
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* Free a ptimer created using ptimer_init().
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*/
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void ptimer_free(ptimer_state *s);
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/**
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* ptimer_transaction_begin() - Start a ptimer modification transaction
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*
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* This function must be called before making any calls to functions
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* which modify the ptimer's state (see the ptimer_init() documentation
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* for a list of these), and must always have a matched call to
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* ptimer_transaction_commit().
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* It is an error to call this function for a BH-based ptimer;
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* attempting to do this will trigger an assert.
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*/
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void ptimer_transaction_begin(ptimer_state *s);
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/**
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* ptimer_transaction_commit() - Commit a ptimer modification transaction
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*
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* This function must be called after calls to functions which modify
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* the ptimer's state, and completes the update of the ptimer. If the
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* ptimer state now means that we should trigger the timer expiry
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* callback, it will be called directly.
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*/
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void ptimer_transaction_commit(ptimer_state *s);
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/**
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* ptimer_set_period - Set counter increment interval in nanoseconds
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* @s: ptimer to configure
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* @period: period of the counter in nanoseconds
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*
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* Note that if your counter behaviour is specified as having a
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* particular frequency rather than a period then ptimer_set_freq()
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* may be more appropriate.
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*
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* This function will assert if it is called outside a
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* ptimer_transaction_begin/commit block.
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*/
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void ptimer_set_period(ptimer_state *s, int64_t period);
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/**
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* ptimer_set_period_from_clock - Set counter increment from a Clock
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* @s: ptimer to configure
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* @clk: pointer to Clock object to take period from
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* @divisor: value to scale the clock frequency down by
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*
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* If the ptimer is being driven from a Clock, this is the preferred
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* way to tell the ptimer about the period, because it avoids any
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* possible rounding errors that might happen if the internal
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* representation of the Clock period was converted to either a period
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* in ns or a frequency in Hz.
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*
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* If the ptimer should run at the same frequency as the clock,
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* pass 1 as the @divisor; if the ptimer should run at half the
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* frequency, pass 2, and so on.
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*
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* This function will assert if it is called outside a
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* ptimer_transaction_begin/commit block.
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*/
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void ptimer_set_period_from_clock(ptimer_state *s, const Clock *clock,
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unsigned int divisor);
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/**
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* ptimer_set_freq - Set counter frequency in Hz
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* @s: ptimer to configure
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* @freq: counter frequency in Hz
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*
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* This does the same thing as ptimer_set_period(), so you only
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* need to call one of them. If the counter behaviour is specified
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* as setting the frequency then this function is more appropriate,
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* because it allows specifying an effective period which is
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* precise to fractions of a nanosecond, avoiding rounding errors.
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*
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* This function will assert if it is called outside a
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* ptimer_transaction_begin/commit block.
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*/
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void ptimer_set_freq(ptimer_state *s, uint32_t freq);
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/**
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* ptimer_get_limit - Get the configured limit of the ptimer
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* @s: ptimer to query
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*
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* This function returns the current limit (reload) value
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* of the down-counter; that is, the value which it will be
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* reset to when it hits zero.
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*
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* Generally timer devices using ptimers should be able to keep
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* their reload register state inside the ptimer using the get
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* and set limit functions rather than needing to also track it
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* in their own state structure.
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*/
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uint64_t ptimer_get_limit(ptimer_state *s);
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/**
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* ptimer_set_limit - Set the limit of the ptimer
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* @s: ptimer
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* @limit: initial countdown value
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* @reload: if nonzero, then reset the counter to the new limit
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*
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* Set the limit value of the down-counter. The @reload flag can
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* be used to emulate the behaviour of timers which immediately
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* reload the counter when their reload register is written to.
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*
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* This function will assert if it is called outside a
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* ptimer_transaction_begin/commit block.
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*/
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void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload);
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/**
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* ptimer_get_count - Get the current value of the ptimer
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* @s: ptimer
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*
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* Return the current value of the down-counter. This will
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* return the correct value whether the counter is enabled or
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* disabled.
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*/
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uint64_t ptimer_get_count(ptimer_state *s);
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/**
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* ptimer_set_count - Set the current value of the ptimer
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* @s: ptimer
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* @count: count value to set
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*
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* Set the value of the down-counter. If the counter is currently
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* enabled this will arrange for a timer callback at the appropriate
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* point in the future.
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*
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* This function will assert if it is called outside a
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* ptimer_transaction_begin/commit block.
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*/
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void ptimer_set_count(ptimer_state *s, uint64_t count);
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/**
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* ptimer_run - Start a ptimer counting
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* @s: ptimer
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* @oneshot: non-zero if this timer should only count down once
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*
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* Start a ptimer counting down; when it reaches zero the callback function
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* passed to ptimer_init() will be invoked.
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* If the @oneshot argument is zero,
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* the counter value will then be reloaded from the limit and it will
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* start counting down again. If @oneshot is non-zero, then the counter
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* will disable itself when it reaches zero.
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*
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* This function will assert if it is called outside a
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* ptimer_transaction_begin/commit block.
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*/
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void ptimer_run(ptimer_state *s, int oneshot);
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/**
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* ptimer_stop - Stop a ptimer counting
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* @s: ptimer
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*
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* Pause a timer (the count stays at its current value until ptimer_run()
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* is called to start it counting again).
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*
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* Note that this can cause it to "lose" time, even if it is immediately
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* restarted.
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*
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* This function will assert if it is called outside a
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* ptimer_transaction_begin/commit block.
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*/
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void ptimer_stop(ptimer_state *s);
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extern const VMStateDescription vmstate_ptimer;
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#define VMSTATE_PTIMER(_field, _state) \
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VMSTATE_STRUCT_POINTER_V(_field, _state, 1, vmstate_ptimer, ptimer_state)
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#define VMSTATE_PTIMER_ARRAY(_f, _s, _n) \
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VMSTATE_ARRAY_OF_POINTER_TO_STRUCT(_f, _s, _n, 0, \
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vmstate_ptimer, ptimer_state)
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#endif
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