1 files changed, 110 insertions, 0 deletions
diff --git a/src/server/FrameTimer.hpp b/src/server/FrameTimer.hpp
new file mode 100644
index 00000000..57acbaa5
--- /dev/null
+++ b/src/server/FrameTimer.hpp
@@ -0,0 +1,110 @@
+/*
+  This file is part of Ingen.
+  Copyright 2017 David Robillard <http://drobilla.net/>
+
+  Ingen is free software: you can redistribute it and/or modify it under the
+  terms of the GNU Affero General Public License as published by the Free
+  Software Foundation, either version 3 of the License, or any later version.
+
+  Ingen is distributed in the hope that it will be useful, but WITHOUT ANY
+  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  A PARTICULAR PURPOSE.  See the GNU Affero General Public License for details.
+
+  You should have received a copy of the GNU Affero General Public License
+  along with Ingen.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef INGEN_ENGINE_FRAMETIMER_HPP
+#define INGEN_ENGINE_FRAMETIMER_HPP
+
+#include <chrono>
+#include <cmath>
+#include <cstdint>
+
+namespace ingen {
+namespace server {
+
+/** Delay-locked loop for monotonic sample time.
+ *
+ * See "Using a DLL to filter time" by Fons Adriaensen
+ * http://kokkinizita.linuxaudio.org/papers/usingdll.pdf
+ */
+class FrameTimer
+{
+public:
+	static constexpr double PI        = 3.14159265358979323846;
+	static constexpr double bandwidth = 1.0 / 8.0; // Hz
+	static constexpr double us_per_s  = 1000000.0;
+
+	FrameTimer(uint32_t period_size, uint32_t sample_rate)
+		: tper(((double)period_size / (double)sample_rate) * us_per_s)
+		, omega(2 * PI * bandwidth / us_per_s * tper)
+		, b(sqrt(2) * omega)
+		, c(omega * omega)
+		, nper(period_size)
+	{
+	}
+
+	/** Update the timer for current real time `usec` and frame `frame`. */
+	void update(uint64_t usec, uint64_t frame) {
+		if (!initialized || frame != n1) {
+			init(usec, frame);
+			return;
+		}
+
+		// Calculate loop error
+		const double e = ((double)usec - t1);
+
+		// Update loop
+		t0 = t1;
+		t1 += b * e + e2;
+		e2 += c * e;
+
+		// Update frame counts
+		n0 = n1;
+		n1 += nper;
+	}
+
+	/** Return an estimate of the frame time for current real time `usec`. */
+	uint64_t frame_time(uint64_t usec) const {
+		if (!initialized) {
+			return 0;
+		}
+
+		const double delta = (double)usec - t0;
+		const double period = t1 - t0;
+		return n0 + std::round(delta / period * nper);
+	}
+
+private:
+	void init(uint64_t now, uint64_t frame) {
+		// Init loop
+		e2 = tper;
+		t0 = now;
+		t1 = t0 + e2;
+
+		// Init sample counts
+		n0 = frame;
+		n1 = n0 + nper;
+
+		initialized = true;
+	}
+
+	const double tper;
+	const double omega;
+	const double b;
+	const double c;
+
+	uint64_t nper;
+	double   e2;
+	double   t0;
+	double   t1;
+	uint64_t n0;
+	uint64_t n1;
+	bool     initialized;
+};
+
+} // namespace server
+} // namespace ingen
+
+#endif // INGEN_ENGINE_FRAMETIMER_HPP