1 /* 2 * Copyright (C) 2012 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef ANDROID_DISPSYNC_H 18 #define ANDROID_DISPSYNC_H 19 20 #include <stddef.h> 21 22 #include <utils/Mutex.h> 23 #include <utils/Timers.h> 24 #include <utils/RefBase.h> 25 26 namespace android { 27 28 // Ignore present (retire) fences if the device doesn't have support for the 29 // sync framework 30 #if defined(RUNNING_WITHOUT_SYNC_FRAMEWORK) 31 static const bool kIgnorePresentFences = true; 32 #else 33 static const bool kIgnorePresentFences = false; 34 #endif 35 36 37 class String8; 38 class Fence; 39 class DispSyncThread; 40 41 // DispSync maintains a model of the periodic hardware-based vsync events of a 42 // display and uses that model to execute period callbacks at specific phase 43 // offsets from the hardware vsync events. The model is constructed by 44 // feeding consecutive hardware event timestamps to the DispSync object via 45 // the addResyncSample method. 46 // 47 // The model is validated using timestamps from Fence objects that are passed 48 // to the DispSync object via the addPresentFence method. These fence 49 // timestamps should correspond to a hardware vsync event, but they need not 50 // be consecutive hardware vsync times. If this method determines that the 51 // current model accurately represents the hardware event times it will return 52 // false to indicate that a resynchronization (via addResyncSample) is not 53 // needed. 54 class DispSync { 55 56 public: 57 58 class Callback: public virtual RefBase { 59 public: ~Callback()60 virtual ~Callback() {}; 61 virtual void onDispSyncEvent(nsecs_t when) = 0; 62 }; 63 64 DispSync(const char* name); 65 ~DispSync(); 66 67 // reset clears the resync samples and error value. 68 void reset(); 69 70 // addPresentFence adds a fence for use in validating the current vsync 71 // event model. The fence need not be signaled at the time 72 // addPresentFence is called. When the fence does signal, its timestamp 73 // should correspond to a hardware vsync event. Unlike the 74 // addResyncSample method, the timestamps of consecutive fences need not 75 // correspond to consecutive hardware vsync events. 76 // 77 // This method should be called with the retire fence from each HWComposer 78 // set call that affects the display. 79 bool addPresentFence(const sp<Fence>& fence); 80 81 // The beginResync, addResyncSample, and endResync methods are used to re- 82 // synchronize the DispSync's model to the hardware vsync events. The re- 83 // synchronization process involves first calling beginResync, then 84 // calling addResyncSample with a sequence of consecutive hardware vsync 85 // event timestamps, and finally calling endResync when addResyncSample 86 // indicates that no more samples are needed by returning false. 87 // 88 // This resynchronization process should be performed whenever the display 89 // is turned on (i.e. once immediately after it's turned on) and whenever 90 // addPresentFence returns true indicating that the model has drifted away 91 // from the hardware vsync events. 92 void beginResync(); 93 bool addResyncSample(nsecs_t timestamp); 94 void endResync(); 95 96 // The setPeriod method sets the vsync event model's period to a specific 97 // value. This should be used to prime the model when a display is first 98 // turned on. It should NOT be used after that. 99 void setPeriod(nsecs_t period); 100 101 // The getPeriod method returns the current vsync period. 102 nsecs_t getPeriod(); 103 104 // setRefreshSkipCount specifies an additional number of refresh 105 // cycles to skip. For example, on a 60Hz display, a skip count of 1 106 // will result in events happening at 30Hz. Default is zero. The idea 107 // is to sacrifice smoothness for battery life. 108 void setRefreshSkipCount(int count); 109 110 // addEventListener registers a callback to be called repeatedly at the 111 // given phase offset from the hardware vsync events. The callback is 112 // called from a separate thread and it should return reasonably quickly 113 // (i.e. within a few hundred microseconds). 114 status_t addEventListener(const char* name, nsecs_t phase, 115 const sp<Callback>& callback); 116 117 // removeEventListener removes an already-registered event callback. Once 118 // this method returns that callback will no longer be called by the 119 // DispSync object. 120 status_t removeEventListener(const sp<Callback>& callback); 121 122 // computeNextRefresh computes when the next refresh is expected to begin. 123 // The periodOffset value can be used to move forward or backward; an 124 // offset of zero is the next refresh, -1 is the previous refresh, 1 is 125 // the refresh after next. etc. 126 nsecs_t computeNextRefresh(int periodOffset) const; 127 128 // dump appends human-readable debug info to the result string. 129 void dump(String8& result) const; 130 131 private: 132 133 void updateModelLocked(); 134 void updateErrorLocked(); 135 void resetErrorLocked(); 136 137 enum { MAX_RESYNC_SAMPLES = 32 }; 138 enum { MIN_RESYNC_SAMPLES_FOR_UPDATE = 6 }; 139 enum { NUM_PRESENT_SAMPLES = 8 }; 140 enum { MAX_RESYNC_SAMPLES_WITHOUT_PRESENT = 4 }; 141 142 const char* const mName; 143 144 // mPeriod is the computed period of the modeled vsync events in 145 // nanoseconds. 146 nsecs_t mPeriod; 147 148 // mPhase is the phase offset of the modeled vsync events. It is the 149 // number of nanoseconds from time 0 to the first vsync event. 150 nsecs_t mPhase; 151 152 // mReferenceTime is the reference time of the modeled vsync events. 153 // It is the nanosecond timestamp of the first vsync event after a resync. 154 nsecs_t mReferenceTime; 155 156 // mError is the computed model error. It is based on the difference 157 // between the estimated vsync event times and those observed in the 158 // mPresentTimes array. 159 nsecs_t mError; 160 161 // Whether we have updated the vsync event model since the last resync. 162 bool mModelUpdated; 163 164 // These member variables are the state used during the resynchronization 165 // process to store information about the hardware vsync event times used 166 // to compute the model. 167 nsecs_t mResyncSamples[MAX_RESYNC_SAMPLES]; 168 size_t mFirstResyncSample; 169 size_t mNumResyncSamples; 170 int mNumResyncSamplesSincePresent; 171 172 // These member variables store information about the present fences used 173 // to validate the currently computed model. 174 sp<Fence> mPresentFences[NUM_PRESENT_SAMPLES]; 175 nsecs_t mPresentTimes[NUM_PRESENT_SAMPLES]; 176 size_t mPresentSampleOffset; 177 178 int mRefreshSkipCount; 179 180 // mThread is the thread from which all the callbacks are called. 181 sp<DispSyncThread> mThread; 182 183 // mMutex is used to protect access to all member variables. 184 mutable Mutex mMutex; 185 }; 186 187 } 188 189 #endif // ANDROID_DISPSYNC_H 190