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 class String8; 29 class Fence; 30 class DispSyncThread; 31 32 // DispSync maintains a model of the periodic hardware-based vsync events of a 33 // display and uses that model to execute period callbacks at specific phase 34 // offsets from the hardware vsync events. The model is constructed by 35 // feeding consecutive hardware event timestamps to the DispSync object via 36 // the addResyncSample method. 37 // 38 // The model is validated using timestamps from Fence objects that are passed 39 // to the DispSync object via the addPresentFence method. These fence 40 // timestamps should correspond to a hardware vsync event, but they need not 41 // be consecutive hardware vsync times. If this method determines that the 42 // current model accurately represents the hardware event times it will return 43 // false to indicate that a resynchronization (via addResyncSample) is not 44 // needed. 45 class DispSync { 46 47 public: 48 49 class Callback: public virtual RefBase { 50 public: 51 virtual ~Callback() {}; 52 virtual void onDispSyncEvent(nsecs_t when) = 0; 53 }; 54 55 explicit DispSync(const char* name); 56 ~DispSync(); 57 58 // reset clears the resync samples and error value. 59 void reset(); 60 61 // addPresentFence adds a fence for use in validating the current vsync 62 // event model. The fence need not be signaled at the time 63 // addPresentFence is called. When the fence does signal, its timestamp 64 // should correspond to a hardware vsync event. Unlike the 65 // addResyncSample method, the timestamps of consecutive fences need not 66 // correspond to consecutive hardware vsync events. 67 // 68 // This method should be called with the retire fence from each HWComposer 69 // set call that affects the display. 70 bool addPresentFence(const sp<Fence>& fence); 71 72 // The beginResync, addResyncSample, and endResync methods are used to re- 73 // synchronize the DispSync's model to the hardware vsync events. The re- 74 // synchronization process involves first calling beginResync, then 75 // calling addResyncSample with a sequence of consecutive hardware vsync 76 // event timestamps, and finally calling endResync when addResyncSample 77 // indicates that no more samples are needed by returning false. 78 // 79 // This resynchronization process should be performed whenever the display 80 // is turned on (i.e. once immediately after it's turned on) and whenever 81 // addPresentFence returns true indicating that the model has drifted away 82 // from the hardware vsync events. 83 void beginResync(); 84 bool addResyncSample(nsecs_t timestamp); 85 void endResync(); 86 87 // The setPeriod method sets the vsync event model's period to a specific 88 // value. This should be used to prime the model when a display is first 89 // turned on. It should NOT be used after that. 90 void setPeriod(nsecs_t period); 91 92 // The getPeriod method returns the current vsync period. 93 nsecs_t getPeriod(); 94 95 // setRefreshSkipCount specifies an additional number of refresh 96 // cycles to skip. For example, on a 60Hz display, a skip count of 1 97 // will result in events happening at 30Hz. Default is zero. The idea 98 // is to sacrifice smoothness for battery life. 99 void setRefreshSkipCount(int count); 100 101 // addEventListener registers a callback to be called repeatedly at the 102 // given phase offset from the hardware vsync events. The callback is 103 // called from a separate thread and it should return reasonably quickly 104 // (i.e. within a few hundred microseconds). 105 status_t addEventListener(const char* name, nsecs_t phase, 106 const sp<Callback>& callback); 107 108 // removeEventListener removes an already-registered event callback. Once 109 // this method returns that callback will no longer be called by the 110 // DispSync object. 111 status_t removeEventListener(const sp<Callback>& callback); 112 113 // computeNextRefresh computes when the next refresh is expected to begin. 114 // The periodOffset value can be used to move forward or backward; an 115 // offset of zero is the next refresh, -1 is the previous refresh, 1 is 116 // the refresh after next. etc. 117 nsecs_t computeNextRefresh(int periodOffset) const; 118 119 // dump appends human-readable debug info to the result string. 120 void dump(String8& result) const; 121 122 private: 123 124 void updateModelLocked(); 125 void updateErrorLocked(); 126 void resetErrorLocked(); 127 128 enum { MAX_RESYNC_SAMPLES = 32 }; 129 enum { MIN_RESYNC_SAMPLES_FOR_UPDATE = 6 }; 130 enum { NUM_PRESENT_SAMPLES = 8 }; 131 enum { MAX_RESYNC_SAMPLES_WITHOUT_PRESENT = 4 }; 132 133 const char* const mName; 134 135 // mPeriod is the computed period of the modeled vsync events in 136 // nanoseconds. 137 nsecs_t mPeriod; 138 139 // mPhase is the phase offset of the modeled vsync events. It is the 140 // number of nanoseconds from time 0 to the first vsync event. 141 nsecs_t mPhase; 142 143 // mReferenceTime is the reference time of the modeled vsync events. 144 // It is the nanosecond timestamp of the first vsync event after a resync. 145 nsecs_t mReferenceTime; 146 147 // mError is the computed model error. It is based on the difference 148 // between the estimated vsync event times and those observed in the 149 // mPresentTimes array. 150 nsecs_t mError; 151 152 // Whether we have updated the vsync event model since the last resync. 153 bool mModelUpdated; 154 155 // These member variables are the state used during the resynchronization 156 // process to store information about the hardware vsync event times used 157 // to compute the model. 158 nsecs_t mResyncSamples[MAX_RESYNC_SAMPLES]; 159 size_t mFirstResyncSample; 160 size_t mNumResyncSamples; 161 int mNumResyncSamplesSincePresent; 162 163 // These member variables store information about the present fences used 164 // to validate the currently computed model. 165 sp<Fence> mPresentFences[NUM_PRESENT_SAMPLES]; 166 nsecs_t mPresentTimes[NUM_PRESENT_SAMPLES]; 167 size_t mPresentSampleOffset; 168 169 int mRefreshSkipCount; 170 171 // mThread is the thread from which all the callbacks are called. 172 sp<DispSyncThread> mThread; 173 174 // mMutex is used to protect access to all member variables. 175 mutable Mutex mMutex; 176 177 // This is the offset from the present fence timestamps to the corresponding 178 // vsync event. 179 int64_t mPresentTimeOffset; 180 181 // Ignore present (retire) fences if the device doesn't have support for the 182 // sync framework 183 bool mIgnorePresentFences; 184 }; 185 186 } 187 188 #endif // ANDROID_DISPSYNC_H 189
