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Merge "Fix SntpClient to give accurate time info." into froyo

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Robert Greenwalt
2010-04-15 13:28:43 -07:00
committed by Android (Google) Code Review
parent 4f99e3c284 499a121c13
commit bf943f2968
1 changed files with 13 additions and 4 deletions
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17
core/java/android/net/SntpClient.java
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@@ -103,13 +103,22 @@ public class SntpClient
long receiveTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET);
long transmitTime = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET);
long roundTripTime = responseTicks - requestTicks - (transmitTime - receiveTime);
long clockOffset = (receiveTime - originateTime) + (transmitTime - responseTime);
// receiveTime = originateTime + transit + skew
// responseTime = transmitTime + transit - skew
// clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2
// = ((originateTime + transit + skew - originateTime) +
// (transmitTime - (transmitTime + transit - skew)))/2
// = ((transit + skew) + (transmitTime - transmitTime - transit + skew))/2
// = (transit + skew - transit + skew)/2
// = (2 * skew)/2 = skew
long clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2;
if (Config.LOGD) Log.d(TAG, "round trip: " + roundTripTime + " ms");
if (Config.LOGD) Log.d(TAG, "clock offset: " + clockOffset + " ms");
// save our results
mNtpTime = requestTime + clockOffset;
mNtpTimeReference = requestTicks;
// save our results - use the times on this side of the network latency
// (response rather than request time)
mNtpTime = responseTime + clockOffset;
mNtpTimeReference = responseTicks;
mRoundTripTime = roundTripTime;
} catch (Exception e) {
if (Config.LOGD) Log.d(TAG, "request time failed: " + e);