CPUClock.hh

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#ifndef CPUCLOCK_HH
#define CPUCLOCK_HH
 
#include "DynamicClock.hh"
#include "Scheduler.hh"
#include "narrow.hh"
#include <cassert>
 
namespace openmsx {
 
class CPUClock
{
public:
        unsigned getFreq() const { return clock.getFreq(); }
 
protected:
        CPUClock(EmuTime::param time, Scheduler& scheduler);
 
// benchmarking showed a slowdown of ~3% on AMD64
// when using the following code:
#if 0
        // 64-bit addition is cheap
        inline void add(unsigned ticks) { clock += ticks; }
        inline void sync() const { }
#else
        // 64-bit addition is expensive
        // (if executed several million times per second)
        inline void add(unsigned ticks) { remaining -= narrow_cast<int>(ticks); }
        inline void sync() const {
                clock.fastAdd(limit - remaining);
                limit = remaining;
        }
#endif
 
        // These are similar to the corresponding methods in DynamicClock.
        [[nodiscard]] EmuTime::param getTime() const { sync(); return clock.getTime(); }
        [[nodiscard]] EmuTime getTimeFast() const { return clock.getFastAdd(limit - remaining); }
        [[nodiscard]] EmuTime getTimeFast(int cc) const {
                return clock.getFastAdd(limit - remaining + cc);
        }
        void setTime(EmuTime::param time) { sync(); clock.reset(time); }
        void setFreq(unsigned freq) { sync(); disableLimit(); clock.setFreq(freq); }
        void advanceTime(EmuTime::param time);
        [[nodiscard]] EmuTime calcTime(EmuTime::param time, unsigned ticks) const {
                return clock.add(time, ticks);
        }
 
        unsigned advanceHalt(unsigned hltStates, EmuTime::param time) {
                sync();
                unsigned ticks = clock.getTicksTillUp(time);
                unsigned halts = (ticks + hltStates - 1) / hltStates; // round up
                clock += halts * hltStates;
                return halts;
        }
 
        void waitForEvenCycle(int cc)
        {
                sync();
                auto totalTicks = clock.getTotalTicks() + cc;
                if (totalTicks & 1) {
                        add(1);
                }
        }
 
        // The following 3 methods are used in the innermost CPU loop. It
        // allows to implement this loop with just one test. This loop must
        // be exited on the following three conditions:
        //   1) a Synchronization Point is reached
        //   2) a 'slow' instruction must be executed (ei, di, ..)
        //   3) another thread has requested to exit the loop
        // The limitReached() method indicates whether the loop should be
        // exited.
        // The earliest SP must always be kept up-to-date with the setLimit()
        // method, so after every action that might change SP. The Scheduler
        // class is responsible for this.
        // In 'slow' mode the limit mechanism can be disabled with the
        // disableLimit() method. In disabled mode, the limitReached() method
        // always returns true.
        // When another thread requests to exit the loop, it's not needed to
        // already exit at the next instruction. If we exit soon that's good
        // enough. This is implemented by simply regularly exiting the loop
        // (outside the inner loop, the real exit condition should be tested).
 
        void setLimit(EmuTime::param time) {
                if (limitEnabled) {
                        sync();
                        assert(remaining == limit);
                        limit = narrow_cast<int>(clock.getTicksTillUp(time) - 1);
                        remaining = limit;
                } else {
                        assert(limit < 0);
                }
        }
        void enableLimit() {
                limitEnabled = true;
                setLimit(scheduler.getNext());
        }
        void disableLimit() {
                limitEnabled = false;
                int extra = limit - remaining;
                limit = -1;
                remaining = limit - extra;
        }
        [[nodiscard]] inline bool limitReached() const {
                return remaining < 0;
        }
 
        template<typename Archive>
        void serialize(Archive& ar, unsigned version);
 
private:
        mutable DynamicClock clock;
        Scheduler& scheduler;
        int remaining = -1;
        mutable int limit = -1;
        bool limitEnabled = false;
};
 
} // namespace openmsx
 
#endif