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: ~Callback()51 virtual ~Callback() {}; 52 virtual void onDispSyncEvent(nsecs_t when) = 0; 53 }; 54 55 DispSync(); 56 ~DispSync(); 57 58 void reset(); 59 60 // addPresentFence adds a fence for use in validating the current vsync 61 // event model. The fence need not be signaled at the time 62 // addPresentFence is called. When the fence does signal, its timestamp 63 // should correspond to a hardware vsync event. Unlike the 64 // addResyncSample method, the timestamps of consecutive fences need not 65 // correspond to consecutive hardware vsync events. 66 // 67 // This method should be called with the retire fence from each HWComposer 68 // set call that affects the display. 69 bool addPresentFence(const sp<Fence>& fence); 70 71 // The beginResync, addResyncSample, and endResync methods are used to re- 72 // synchronize the DispSync's model to the hardware vsync events. The re- 73 // synchronization process involves first calling beginResync, then 74 // calling addResyncSample with a sequence of consecutive hardware vsync 75 // event timestamps, and finally calling endResync when addResyncSample 76 // indicates that no more samples are needed by returning false. 77 // 78 // This resynchronization process should be performed whenever the display 79 // is turned on (i.e. once immediately after it's turned on) and whenever 80 // addPresentFence returns true indicating that the model has drifted away 81 // from the hardware vsync events. 82 void beginResync(); 83 bool addResyncSample(nsecs_t timestamp); 84 void endResync(); 85 86 // The setPreiod method sets the vsync event model's period to a specific 87 // value. This should be used to prime the model when a display is first 88 // turned on. It should NOT be used after that. 89 void setPeriod(nsecs_t period); 90 91 // addEventListener registers a callback to be called repeatedly at the 92 // given phase offset from the hardware vsync events. The callback is 93 // called from a separate thread and it should return reasonably quickly 94 // (i.e. within a few hundred microseconds). 95 status_t addEventListener(nsecs_t phase, const sp<Callback>& callback); 96 97 // removeEventListener removes an already-registered event callback. Once 98 // this method returns that callback will no longer be called by the 99 // DispSync object. 100 status_t removeEventListener(const sp<Callback>& callback); 101 102 private: 103 104 void updateModelLocked(); 105 void updateErrorLocked(); 106 void resetErrorLocked(); 107 108 enum { MAX_RESYNC_SAMPLES = 32 }; 109 enum { MIN_RESYNC_SAMPLES_FOR_UPDATE = 3 }; 110 enum { NUM_PRESENT_SAMPLES = 8 }; 111 enum { MAX_RESYNC_SAMPLES_WITHOUT_PRESENT = 12 }; 112 113 // mPeriod is the computed period of the modeled vsync events in 114 // nanoseconds. 115 nsecs_t mPeriod; 116 117 // mPhase is the phase offset of the modeled vsync events. It is the 118 // number of nanoseconds from time 0 to the first vsync event. 119 nsecs_t mPhase; 120 121 // mError is the computed model error. It is based on the difference 122 // between the estimated vsync event times and those observed in the 123 // mPresentTimes array. 124 nsecs_t mError; 125 126 // These member variables are the state used during the resynchronization 127 // process to store information about the hardware vsync event times used 128 // to compute the model. 129 nsecs_t mResyncSamples[MAX_RESYNC_SAMPLES]; 130 size_t mFirstResyncSample; 131 size_t mNumResyncSamples; 132 int mNumResyncSamplesSincePresent; 133 134 // These member variables store information about the present fences used 135 // to validate the currently computed model. 136 sp<Fence> mPresentFences[NUM_PRESENT_SAMPLES]; 137 nsecs_t mPresentTimes[NUM_PRESENT_SAMPLES]; 138 size_t mPresentSampleOffset; 139 140 // mThread is the thread from which all the callbacks are called. 141 sp<DispSyncThread> mThread; 142 143 // mMutex is used to protect access to all member variables. 144 mutable Mutex mMutex; 145 }; 146 147 } 148 149 #endif // ANDROID_DISPSYNC_H 150