Accumulators wait for the next sample after reset

Analog accumulators now wait for the amount of time a full sample
(including oversampling and averaging) lasts after
AnalogInput::ResetAccumulator() is called, so they don't return
old values after being reset.

This delay should be microseconds long and will only happen
when an accumulator is reset.

A new test is is the C++ TiltPanCameraTest that tests this behavior
with the Gyro class.

Change-Id: I1b3ffdeec187959f95c5e637a6d428c9a4bc2cf4

wpilibc/wpilibC++/lib/AnalogInput.cpp

@@ -7,6 +7,7 @@
 #include "AnalogInput.h"
 //#include "NetworkCommunication/UsageReporting.h"
 #include "Resource.h"
+#include "Timer.h"
 #include "WPIErrors.h"
 #include "LiveWindow/LiveWindow.h"
 
@@ -284,6 +285,16 @@ void AnalogInput::ResetAccumulator()
 	int32_t status = 0;
 	resetAccumulator(m_port, &status);
 	wpi_setErrorWithContext(status, getHALErrorMessage(status));
+
+	if(!StatusIsFatal())
+	{
+		// Wait until the next sample, so the next call to GetAccumulator*()
+		// won't have old values.
+		const float sampleTime = 1.0f / GetSampleRate();
+		const float overSamples = 1 << GetOversampleBits();
+		const float averageSamples = 1 << GetAverageBits();
+		Wait(sampleTime * overSamples * averageSamples);
+	}
 }
 
 /**

wpilibc/wpilibC++IntegrationTests/src/TiltPanCameraTest.cpp

@@ -9,7 +9,7 @@
 #include "gtest/gtest.h"
 #include "TestBench.h"
 
-static constexpr double kServoResetTime = 1.0;
+static constexpr double kServoResetTime = 2.0;
 
 static constexpr double kTestAngle = 180.0;
 
@@ -44,6 +44,13 @@ protected:
 		m_tilt = new Servo(TestBench::kCameraTiltChannel);
 		m_pan = new Servo(TestBench::kCameraPanChannel);
 		m_spiAccel = new ADXL345_SPI(SPI::kOnboardCS0);
+
+		m_tilt->SetAngle(90.0f);
+		m_pan->SetAngle(0.0f);
+
+		Wait(kServoResetTime);
+
+		m_gyro->Reset();
 	}
 
 	virtual void TearDown() {
@@ -55,15 +62,17 @@ protected:
 
 Gyro *TiltPanCameraTest::m_gyro = 0;
 
+/**
+ * Test if the gyro angle defaults to 0 immediately after being reset.
+ */
+TEST_F(TiltPanCameraTest, DefaultGyroAngle) {
+	EXPECT_NEAR(0.0f, m_gyro->GetAngle(), 0.01f);
+}
+
 /**
  * Test if the servo turns 180 degrees and the gyroscope measures this angle
  */
 TEST_F(TiltPanCameraTest, GyroAngle) {
-	m_pan->Set(0.0f);
-	Wait(kServoResetTime);
-
-	m_gyro->Reset();
-
 	for(int i = 0; i < 180; i++) {
 		m_pan->SetAngle(i);
 

wpilibj/wpilibJavaDevices/src/main/java/edu/wpi/first/wpilibj/AnalogInput.java

@@ -310,6 +310,14 @@ public class AnalogInput extends SensorBase implements PIDSource,
 		status.order(ByteOrder.LITTLE_ENDIAN);
 		AnalogJNI.resetAccumulator(m_port, status.asIntBuffer());
 		HALUtil.checkStatus(status.asIntBuffer());
+
+		// Wait until the next sample, so the next call to getAccumulator*()
+		// won't have old values.
+		final double sampleTime = 1.0 / getGlobalSampleRate();
+		final double overSamples = 1 << getOversampleBits();
+		final double averageSamples = 1 << getAverageBits();
+		Timer.delay(sampleTime * overSamples * averageSamples);
+
 	}
 
 	/**