clock_recovery.h revision 26fddcd74252bdda95dd7c3f819353e79c622012 
1/*
2 * Copyright (C) 2011 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 __CLOCK_RECOVERY_H__
18#define __CLOCK_RECOVERY_H__
19
20#include <stdint.h>
21#include <common_time/ICommonClock.h>
22#include <utils/threads.h>
23
24#include "LinearTransform.h"
25
26#ifdef TIME_SERVICE_DEBUG
27#include "diag_thread.h"
28#endif
29
30#include "utils.h"
31
32namespace android {
33
34class CommonClock;
35class LocalClock;
36
37class ClockRecoveryLoop {
38  public:
39     ClockRecoveryLoop(LocalClock* local_clock, CommonClock* common_clock);
40    ~ClockRecoveryLoop();
41
42    void reset(bool position, bool frequency);
43    bool pushDisciplineEvent(int64_t local_time,
44                             int64_t nominal_common_time,
45                             int64_t data_point_rtt);
46    int32_t getLastErrorEstimate();
47
48    // Applies the next step in any ongoing slew change operation.  Returns a
49    // timeout suitable for use with poll/select indicating the number of mSec
50    // until the next change should be applied.
51    int applyRateLimitedSlew();
52
53  private:
54
55    // Tuned using the "Good Gain" method.
56    // See:
57    // http://techteach.no/publications/books/dynamics_and_control/tuning_pid_controller.pdf
58
59    // Controller period (1Hz for now).
60    static const float dT;
61
62    // Controller gain, positive and unitless. Larger values converge faster,
63    // but can cause instability.
64    static const float Kc;
65
66    // Integral reset time. Smaller values cause loop to track faster, but can
67    // also cause instability.
68    static const float Ti;
69
70    // Controller output filter time constant. Range (0-1). Smaller values make
71    // output smoother, but slow convergence.
72    static const float Tf;
73
74    // Low-pass filter for bias tracker.
75    static const float bias_Fc; // HZ
76    static const float bias_RC; // Computed in constructor.
77    static const float bias_Alpha; // Computed inconstructor.
78
79    // The maximum allowed error (as indicated by a  pushDisciplineEvent) before
80    // we panic.
81    static const int64_t panic_thresh_;
82
83    // The maximum allowed error rtt time for packets to be used for control
84    // feedback, unless the packet is the best in recent memory.
85    static const int64_t control_thresh_;
86
87    typedef struct {
88        int64_t local_time;
89        int64_t observed_common_time;
90        int64_t nominal_common_time;
91        int64_t rtt;
92        bool point_used;
93    } DisciplineDataPoint;
94
95    static uint32_t findMinRTTNdx(DisciplineDataPoint* data, uint32_t count);
96
97    void reset_l(bool position, bool frequency);
98    void setTargetCorrection_l(int32_t tgt);
99    bool applySlew_l();
100
101    // The local clock HW abstraction we use as the basis for common time.
102    LocalClock* local_clock_;
103    bool local_clock_can_slew_;
104
105    // The common clock we end up controlling along with the lock used to
106    // serialize operations.
107    CommonClock* common_clock_;
108    Mutex lock_;
109
110    // parameters maintained while running and reset during a reset
111    // of the frequency correction.
112    bool    last_error_est_valid_;
113    int32_t last_error_est_usec_;
114    float last_delta_f_;
115    int32_t tgt_correction_;
116    int32_t cur_correction_;
117    LinearTransform time_to_cur_slew_;
118    int64_t slew_change_end_time_;
119    Timeout next_slew_change_timeout_;
120
121    // Contoller Output.
122    float CO;
123
124    // Bias tracking for trajectory estimation.
125    float CObias;
126    float lastCObias;
127
128    // Controller output bounds. The controller will not try to
129    // slew faster that +/-100ppm offset from center per interation.
130    static const float COmin;
131    static const float COmax;
132
133    // State kept for filtering the discipline data.
134    static const uint32_t kFilterSize = 16;
135    DisciplineDataPoint filter_data_[kFilterSize];
136    uint32_t filter_wr_;
137    bool filter_full_;
138
139    static const uint32_t kStartupFilterSize = 4;
140    DisciplineDataPoint startup_filter_data_[kStartupFilterSize];
141    uint32_t startup_filter_wr_;
142
143    // Minimum number of milliseconds over which we allow a full range change
144    // (from rail to rail) of the VCXO control signal.  This is the rate
145    // limiting factor which keeps us from changing the clock rate so fast that
146    // we get in trouble with certain HDMI sinks.
147    static const uint32_t kMinFullRangeSlewChange_mSec;
148
149    // How much time (in msec) to wait
150    static const int kSlewChangeStepPeriod_mSec;
151
152#ifdef TIME_SERVICE_DEBUG
153    sp<DiagThread> diag_thread_;
154#endif
155};
156
157}  // namespace android
158
159#endif  // __CLOCK_RECOVERY_H__
160