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a3696c0b91
lib/sysdep: clean up by moving OS and cpu-arch folders into "os" and "arch" folders This was SVN commit r6162.
85 lines
2 KiB
C++
85 lines
2 KiB
C++
/**
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* =========================================================================
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* File : tgt.cpp
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* Project : 0 A.D.
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* Description : Timer implementation using timeGetTime
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* =========================================================================
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*/
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// license: GPL; see lib/license.txt
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// note: WinMM is delay-loaded to avoid dragging it in when this timer
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// implementation isn't used. (this is relevant because its startup is
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// fairly slow)
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#include "precompiled.h"
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#include "tgt.h"
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#include "lib/sysdep/os/win/win.h"
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#include <mmsystem.h>
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#if MSC_VERSION
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#pragma comment(lib, "winmm.lib")
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#endif
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// "Guidelines For Providing Multimedia Timer Support" claims that
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// speeding the timer up to 2 ms has little impact, while 1 ms
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// causes significant slowdown.
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static const UINT PERIOD_MS = 2;
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LibError CounterTGT::Activate()
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{
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// note: timeGetTime is always available and cannot fail.
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MMRESULT ret = timeBeginPeriod(PERIOD_MS);
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debug_assert(ret == TIMERR_NOERROR);
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return INFO::OK;
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}
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void CounterTGT::Shutdown()
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{
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timeEndPeriod(PERIOD_MS);
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}
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bool CounterTGT::IsSafe() const
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{
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// the only point of criticism is the possibility of falling behind
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// due to lost interrupts. this can happen to any interrupt-based timer
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// and some systems may lack a counter-based timer, so consider TGT
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// 'safe'. note that it is still only chosen when all other timers fail.
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return true;
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}
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u64 CounterTGT::Counter() const
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{
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return timeGetTime();
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}
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/**
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* WHRT uses this to ensure the counter (running at nominal frequency)
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* doesn't overflow more than once during CALIBRATION_INTERVAL_MS.
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**/
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size_t CounterTGT::CounterBits() const
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{
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return 32;
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}
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/**
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* initial measurement of the tick rate. not necessarily correct
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* (e.g. when using TSC: os_cpu_ClockFrequency isn't exact).
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**/
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double CounterTGT::NominalFrequency() const
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{
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return 1000.0;
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}
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/**
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* actual resolution [s]
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**/
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double CounterTGT::Resolution() const
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{
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return PERIOD_MS*1e-3;
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}
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