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 /* 18 * A service that exchanges time synchronization information between 19 * a master that defines a timeline and clients that follow the timeline. 20 */ 21 22 #define __STDC_LIMIT_MACROS 23 #define LOG_TAG "common_time" 24 #include <utils/Log.h> 25 #include <stdint.h> 26 27 #include <common_time/local_clock.h> 28 #include <assert.h> 29 30 #include "clock_recovery.h" 31 #include "common_clock.h" 32 #ifdef TIME_SERVICE_DEBUG 33 #include "diag_thread.h" 34 #endif 35 36 // Define log macro so we can make LOGV into LOGE when we are exclusively 37 // debugging this code. 38 #ifdef TIME_SERVICE_DEBUG 39 #define LOG_TS ALOGE 40 #else 41 #define LOG_TS ALOGV 42 #endif 43 44 namespace android { 45 46 ClockRecoveryLoop::ClockRecoveryLoop(LocalClock* local_clock, 47 CommonClock* common_clock) { 48 assert(NULL != local_clock); 49 assert(NULL != common_clock); 50 51 local_clock_ = local_clock; 52 common_clock_ = common_clock; 53 54 local_clock_can_slew_ = local_clock_->initCheck() && 55 (local_clock_->setLocalSlew(0) == OK); 56 tgt_correction_ = 0; 57 cur_correction_ = 0; 58 59 // Precompute the max rate at which we are allowed to change the VCXO 60 // control. 61 uint64_t N = 0x10000ull * 1000ull; 62 uint64_t D = local_clock_->getLocalFreq() * kMinFullRangeSlewChange_mSec; 63 LinearTransform::reduce(&N, &D); 64 while ((N > INT32_MAX) || (D > UINT32_MAX)) { 65 N >>= 1; 66 D >>= 1; 67 LinearTransform::reduce(&N, &D); 68 } 69 time_to_cur_slew_.a_to_b_numer = static_cast<int32_t>(N); 70 time_to_cur_slew_.a_to_b_denom = static_cast<uint32_t>(D); 71 72 reset(true, true); 73 74 #ifdef TIME_SERVICE_DEBUG 75 diag_thread_ = new DiagThread(common_clock_, local_clock_); 76 if (diag_thread_ != NULL) { 77 status_t res = diag_thread_->startWorkThread(); 78 if (res != OK) 79 ALOGW("Failed to start A@H clock recovery diagnostic thread."); 80 } else 81 ALOGW("Failed to allocate diagnostic thread."); 82 #endif 83 } 84 85 ClockRecoveryLoop::~ClockRecoveryLoop() { 86 #ifdef TIME_SERVICE_DEBUG 87 diag_thread_->stopWorkThread(); 88 #endif 89 } 90 91 // Constants. 92 const float ClockRecoveryLoop::dT = 1.0; 93 const float ClockRecoveryLoop::Kc = 1.0f; 94 const float ClockRecoveryLoop::Ti = 15.0f; 95 const float ClockRecoveryLoop::Tf = 0.05; 96 const float ClockRecoveryLoop::bias_Fc = 0.01; 97 const float ClockRecoveryLoop::bias_RC = (dT / (2 * 3.14159f * bias_Fc)); 98 const float ClockRecoveryLoop::bias_Alpha = (dT / (bias_RC + dT)); 99 const int64_t ClockRecoveryLoop::panic_thresh_ = 50000; 100 const int64_t ClockRecoveryLoop::control_thresh_ = 10000; 101 const float ClockRecoveryLoop::COmin = -100.0f; 102 const float ClockRecoveryLoop::COmax = 100.0f; 103 const uint32_t ClockRecoveryLoop::kMinFullRangeSlewChange_mSec = 300; 104 const int ClockRecoveryLoop::kSlewChangeStepPeriod_mSec = 10; 105 106 107 void ClockRecoveryLoop::reset(bool position, bool frequency) { 108 Mutex::Autolock lock(&lock_); 109 reset_l(position, frequency); 110 } 111 112 uint32_t ClockRecoveryLoop::findMinRTTNdx(DisciplineDataPoint* data, 113 uint32_t count) { 114 uint32_t min_rtt = 0; 115 for (uint32_t i = 1; i < count; ++i) 116 if (data[min_rtt].rtt > data[i].rtt) 117 min_rtt = i; 118 119 return min_rtt; 120 } 121 122 bool ClockRecoveryLoop::pushDisciplineEvent(int64_t local_time, 123 int64_t nominal_common_time, 124 int64_t rtt) { 125 Mutex::Autolock lock(&lock_); 126 127 int64_t local_common_time = 0; 128 common_clock_->localToCommon(local_time, &local_common_time); 129 int64_t raw_delta = nominal_common_time - local_common_time; 130 131 #ifdef TIME_SERVICE_DEBUG 132 ALOGE("local=%lld, common=%lld, delta=%lld, rtt=%lld\n", 133 local_common_time, nominal_common_time, 134 raw_delta, rtt); 135 #endif 136 137 // If we have not defined a basis for common time, then we need to use these 138 // initial points to do so. In order to avoid significant initial error 139 // from a particularly bad startup data point, we collect the first N data 140 // points and choose the best of them before moving on. 141 if (!common_clock_->isValid()) { 142 if (startup_filter_wr_ < kStartupFilterSize) { 143 DisciplineDataPoint& d = startup_filter_data_[startup_filter_wr_]; 144 d.local_time = local_time; 145 d.nominal_common_time = nominal_common_time; 146 d.rtt = rtt; 147 startup_filter_wr_++; 148 } 149 150 if (startup_filter_wr_ == kStartupFilterSize) { 151 uint32_t min_rtt = findMinRTTNdx(startup_filter_data_, 152 kStartupFilterSize); 153 154 common_clock_->setBasis( 155 startup_filter_data_[min_rtt].local_time, 156 startup_filter_data_[min_rtt].nominal_common_time); 157 } 158 159 return true; 160 } 161 162 int64_t observed_common; 163 int64_t delta; 164 float delta_f, dCO; 165 int32_t tgt_correction; 166 167 if (OK != common_clock_->localToCommon(local_time, &observed_common)) { 168 // Since we just checked to make certain that this conversion was valid, 169 // and no one else in the system should be messing with it, if this 170 // conversion is suddenly invalid, it is a good reason to panic. 171 ALOGE("Failed to convert local time to common time in %s:%d", 172 __PRETTY_FUNCTION__, __LINE__); 173 return false; 174 } 175 176 // Implement a filter which should match NTP filtering behavior when a 177 // client is associated with only one peer of lower stratum. Basically, 178 // always use the best of the N last data points, where best is defined as 179 // lowest round trip time. NTP uses an N of 8; we use a value of 6. 180 // 181 // TODO(johngro) : experiment with other filter strategies. The goal here 182 // is to mitigate the effects of high RTT data points which typically have 183 // large asymmetries in the TX/RX legs. Downside of the existing NTP 184 // approach (particularly because of the PID controller we are using to 185 // produce the control signal from the filtered data) are that the rate at 186 // which discipline events are actually acted upon becomes irregular and can 187 // become drawn out (the time between actionable event can go way up). If 188 // the system receives a strong high quality data point, the proportional 189 // component of the controller can produce a strong correction which is left 190 // in place for too long causing overshoot. In addition, the integral 191 // component of the system currently is an approximation based on the 192 // assumption of a more or less homogeneous sampling of the error. Its 193 // unclear what the effect of undermining this assumption would be right 194 // now. 195 196 // Two ideas which come to mind immediately would be to... 197 // 1) Keep a history of more data points (32 or so) and ignore data points 198 // whose RTT is more than a certain number of standard deviations outside 199 // of the norm. 200 // 2) Eliminate the PID controller portion of this system entirely. 201 // Instead, move to a system which uses a very wide filter (128 data 202 // points or more) with a sum-of-least-squares line fitting approach to 203 // tracking the long term drift. This would take the place of the I 204 // component in the current PID controller. Also use a much more narrow 205 // outlier-rejector filter (as described in #1) to drive a short term 206 // correction factor similar to the P component of the PID controller. 207 assert(filter_wr_ < kFilterSize); 208 filter_data_[filter_wr_].local_time = local_time; 209 filter_data_[filter_wr_].observed_common_time = observed_common; 210 filter_data_[filter_wr_].nominal_common_time = nominal_common_time; 211 filter_data_[filter_wr_].rtt = rtt; 212 filter_data_[filter_wr_].point_used = false; 213 uint32_t current_point = filter_wr_; 214 filter_wr_ = (filter_wr_ + 1) % kFilterSize; 215 if (!filter_wr_) 216 filter_full_ = true; 217 218 uint32_t scan_end = filter_full_ ? kFilterSize : filter_wr_; 219 uint32_t min_rtt = findMinRTTNdx(filter_data_, scan_end); 220 // We only use packets with low RTTs for control. If the packet RTT 221 // is less than the panic threshold, we can probably eat the jitter with the 222 // control loop. Otherwise, take the packet only if it better than all 223 // of the packets we have in the history. That way we try to track 224 // something, even if it is noisy. 225 if (current_point == min_rtt || rtt < control_thresh_) { 226 delta_f = delta = nominal_common_time - observed_common; 227 228 last_error_est_valid_ = true; 229 last_error_est_usec_ = delta; 230 231 // Compute the error then clamp to the panic threshold. If we ever 232 // exceed this amt of error, its time to panic and reset the system. 233 // Given that the error in the measurement of the error could be as 234 // high as the RTT of the data point, we don't actually panic until 235 // the implied error (delta) is greater than the absolute panic 236 // threashold plus the RTT. IOW - we don't panic until we are 237 // absoluely sure that our best case sync is worse than the absolute 238 // panic threshold. 239 int64_t effective_panic_thresh = panic_thresh_ + rtt; 240 if ((delta > effective_panic_thresh) || 241 (delta < -effective_panic_thresh)) { 242 // PANIC!!! 243 reset_l(false, true); 244 return false; 245 } 246 247 } else { 248 // We do not have a good packet to look at, but we also do not want to 249 // free-run the clock at some crazy slew rate. So we guess the 250 // trajectory of the clock based on the last controller output and the 251 // estimated bias of our clock against the master. 252 // The net effect of this is that CO == CObias after some extended 253 // period of no feedback. 254 delta_f = last_delta_f_ - dT*(CO - CObias); 255 delta = delta_f; 256 } 257 258 // Velocity form PI control equation. 259 dCO = Kc * (1.0f + dT/Ti) * delta_f - Kc * last_delta_f_; 260 CO += dCO * Tf; // Filter CO by applying gain <1 here. 261 262 // Save error terms for later. 263 last_delta_f_ = delta_f; 264 265 // Clamp CO to +/- 100ppm. 266 if (CO < COmin) 267 CO = COmin; 268 else if (CO > COmax) 269 CO = COmax; 270 271 // Update the controller bias. 272 CObias = bias_Alpha * CO + (1.0f - bias_Alpha) * lastCObias; 273 lastCObias = CObias; 274 275 // Convert PPM to 16-bit int range. Add some guard band (-0.01) so we 276 // don't get fp weirdness. 277 tgt_correction = CO * 327.66; 278 279 // If there was a change in the amt of correction to use, update the 280 // system. 281 setTargetCorrection_l(tgt_correction); 282 283 LOG_TS("clock_loop %lld %f %f %f %d\n", raw_delta, delta_f, CO, CObias, tgt_correction); 284 285 #ifdef TIME_SERVICE_DEBUG 286 diag_thread_->pushDisciplineEvent( 287 local_time, 288 observed_common, 289 nominal_common_time, 290 tgt_correction, 291 rtt); 292 #endif 293 294 return true; 295 } 296 297 int32_t ClockRecoveryLoop::getLastErrorEstimate() { 298 Mutex::Autolock lock(&lock_); 299 300 if (last_error_est_valid_) 301 return last_error_est_usec_; 302 else 303 return ICommonClock::kErrorEstimateUnknown; 304 } 305 306 void ClockRecoveryLoop::reset_l(bool position, bool frequency) { 307 assert(NULL != common_clock_); 308 309 if (position) { 310 common_clock_->resetBasis(); 311 startup_filter_wr_ = 0; 312 } 313 314 if (frequency) { 315 last_error_est_valid_ = false; 316 last_error_est_usec_ = 0; 317 last_delta_f_ = 0.0; 318 CO = 0.0f; 319 lastCObias = CObias = 0.0f; 320 setTargetCorrection_l(0); 321 applySlew_l(); 322 } 323 324 filter_wr_ = 0; 325 filter_full_ = false; 326 } 327 328 void ClockRecoveryLoop::setTargetCorrection_l(int32_t tgt) { 329 // When we make a change to the slew rate, we need to be careful to not 330 // change it too quickly as it can anger some HDMI sinks out there, notably 331 // some Sony panels from the 2010-2011 timeframe. From experimenting with 332 // some of these sinks, it seems like swinging from one end of the range to 333 // another in less that 190mSec or so can start to cause trouble. Adding in 334 // a hefty margin, we limit the system to a full range sweep in no less than 335 // 300mSec. 336 if (tgt_correction_ != tgt) { 337 int64_t now = local_clock_->getLocalTime(); 338 status_t res; 339 340 tgt_correction_ = tgt; 341 342 // Set up the transformation to figure out what the slew should be at 343 // any given point in time in the future. 344 time_to_cur_slew_.a_zero = now; 345 time_to_cur_slew_.b_zero = cur_correction_; 346 347 // Make sure the sign of the slope is headed in the proper direction. 348 bool needs_increase = (cur_correction_ < tgt_correction_); 349 bool is_increasing = (time_to_cur_slew_.a_to_b_numer > 0); 350 if (( needs_increase && !is_increasing) || 351 (!needs_increase && is_increasing)) { 352 time_to_cur_slew_.a_to_b_numer = -time_to_cur_slew_.a_to_b_numer; 353 } 354 355 // Finally, figure out when the change will be finished and start the 356 // slew operation. 357 time_to_cur_slew_.doReverseTransform(tgt_correction_, 358 &slew_change_end_time_); 359 360 applySlew_l(); 361 } 362 } 363 364 bool ClockRecoveryLoop::applySlew_l() { 365 bool ret = true; 366 367 // If cur == tgt, there is no ongoing sleq rate change and we are already 368 // finished. 369 if (cur_correction_ == tgt_correction_) 370 goto bailout; 371 372 if (local_clock_can_slew_) { 373 int64_t now = local_clock_->getLocalTime(); 374 int64_t tmp; 375 376 if (now >= slew_change_end_time_) { 377 cur_correction_ = tgt_correction_; 378 next_slew_change_timeout_.setTimeout(-1); 379 } else { 380 time_to_cur_slew_.doForwardTransform(now, &tmp); 381 382 if (tmp > INT16_MAX) 383 cur_correction_ = INT16_MAX; 384 else if (tmp < INT16_MIN) 385 cur_correction_ = INT16_MIN; 386 else 387 cur_correction_ = static_cast<int16_t>(tmp); 388 389 next_slew_change_timeout_.setTimeout(kSlewChangeStepPeriod_mSec); 390 ret = false; 391 } 392 393 local_clock_->setLocalSlew(cur_correction_); 394 } else { 395 // Since we are not actually changing the rate of a HW clock, we don't 396 // need to worry to much about changing the slew rate so fast that we 397 // anger any downstream HDMI devices. 398 cur_correction_ = tgt_correction_; 399 next_slew_change_timeout_.setTimeout(-1); 400 401 // The SW clock recovery implemented by the common clock class expects 402 // values expressed in PPM. CO is in ppm. 403 common_clock_->setSlew(local_clock_->getLocalTime(), CO); 404 } 405 406 bailout: 407 return ret; 408 } 409 410 int ClockRecoveryLoop::applyRateLimitedSlew() { 411 Mutex::Autolock lock(&lock_); 412 413 int ret = next_slew_change_timeout_.msecTillTimeout(); 414 if (!ret) { 415 if (applySlew_l()) 416 next_slew_change_timeout_.setTimeout(-1); 417 ret = next_slew_change_timeout_.msecTillTimeout(); 418 } 419 420 return ret; 421 } 422 423 } // namespace android 424
