only rely on history if clock_offset is stable

server/driver/clock_offset.cpp

@@ -126,8 +126,13 @@ void clock_offset_estimator::add_sample(const xrt::drivers::wivrn::from_headset:
 	double a = cov / v;
 	double b = mean_y - a * mean_x;
 
+	b = y0 + b - int64_t(a * x0);
+
+	// a changed less than 1% and b changed less than 200ms
+	offset.stable = std::abs((a - offset.a) / offset.a) < 0.01 && std::abs((b - (double)offset.b)) < 200'000'000;
+
 	offset.a = a;
-	offset.b = y0 + b - int64_t(a * x0);
+	offset.b = b;
 	U_LOG_D("clock relations: headset = a*x+b where a=%f b=%ldµs", offset.a, offset.b / 1000);
 }
 
@@ -146,3 +151,8 @@ XrTime clock_offset::to_headset(XrTime timestamp_ns) const
 {
 	return a * timestamp_ns + b;
 }
+
+bool clock_offset::is_stable() const
+{
+	return stable;
+}

server/driver/clock_offset.h

@@ -35,6 +35,7 @@ struct clock_offset
 	// y = ax+b
 	int64_t b = 0;
 	double a = 1;
+	bool stable = false;
 
 	operator bool() const
 	{
@@ -44,6 +45,8 @@ struct clock_offset
 	XrTime from_headset(XrTime) const;
 
 	XrTime to_headset(XrTime timestamp_ns) const;
+
+	bool is_stable() const;
 };
 
 class clock_offset_estimator

server/driver/history.h

@@ -20,6 +20,7 @@
 #pragma once
 
 #include "clock_offset.h"
+#include "util/u_logging.h"
 #include <algorithm>
 #include <cstddef>
 #include <list>
@@ -47,6 +48,15 @@ class history
 		// Discard outdated data, packets could be reordered
 		if (not data.empty())
 		{
+			// keep only one sample if the clock_offset is unstable
+			if (!offset.is_stable())
+			{
+				U_LOG_D("not using history: clock_offset not stable");
+				data.clear();
+				data.emplace_back(sample, produced, t);
+				return;
+			}
+
 			if (data.back().produced_timestamp > produced)
 				return;
 		}