src/oscilloscope.cpp: Fix crash in streaming mode.

After 200ms/div, the tool enters streaming mode, which makes use of
kernel buffers to acquire data in smaller chunks.
There are 2 scenarios:
-the trigger is inside the visible buffer and the buffer size is
restricted by the trigger value;
-the trigger is 0, which means we get to manipulate the best values
for buffersize and number of kernel buffers.

Also, the time position handle needs some limits when the time base is
over the timebase threshold.

Signed-off-by: Alexandra Trifan <Alexandra.Trifan@analog.com>

Author: AlexandraTrifan

src/oscilloscope.cpp

@@ -98,6 +98,9 @@ using namespace libm2k;
 using namespace libm2k::context;
 using namespace std::placeholders;
 
+constexpr int MAX_BUFFER_SIZE_STREAM = 1024 * 1024;
+constexpr int MAX_KERNEL_BUFFERS = 64;
+
 Oscilloscope::Oscilloscope(struct iio_context *ctx, Filter *filt,
 			   ToolMenuItem *toolMenuItem,
 			   QJSEngine *engine, ToolLauncher *parent) :
@@ -159,7 +162,7 @@ Oscilloscope::Oscilloscope(struct iio_context *ctx, Filter *filt,
 	if (m_m2k_analogin) {
 		symmBufferMode = make_shared<SymmetricBufferMode>();
 		symmBufferMode->setSampleRates(m_m2k_analogin->getAvailableSampleRates());
-		symmBufferMode->setEntireBufferMaxSize(64000);
+		symmBufferMode->setEntireBufferMaxSize(MAX_BUFFER_SIZE_STREAM);
 		symmBufferMode->setTriggerBufferMaxSize(8192); // 8192 is what hardware supports
 		symmBufferMode->setTimeDivisionCount(plot.xAxisNumDiv());
 	}
@@ -547,7 +550,7 @@ Oscilloscope::Oscilloscope(struct iio_context *ctx, Filter *filt,
 				{"h", 36E2}
 				}, tr("Position"),
 				-timeBase->maxValue() * 5,
-				36E2,
+				36E3,
 				true, false, this);
 	voltsPerDiv = new ScaleSpinButton({
 //				{"μVolts", 1E-6},
@@ -563,8 +566,8 @@ Oscilloscope::Oscilloscope(struct iio_context *ctx, Filter *filt,
 				-25, 25, true, false, this);
 
 	plot.setOffsetInterval(-DBL_MAX, DBL_MAX);
-	plot.setTimeTriggerInterval(-timeBase->maxValue() * 5,
-				     timeBase->maxValue() * 5);
+	plot.setTimeTriggerInterval(-36E2,
+				    timeBase->maxValue() * 5);
 
 	ch_ui = new Ui::ChannelSettings();
 	ch_ui->setupUi(ui->channelSettings);
@@ -3594,7 +3597,7 @@ void Oscilloscope::onCmbMemoryDepthChanged(QString value)
 		power = ceil(log2(active_plot_sample_count));
 	}
 	fft_plot_size = pow(2, power);
-	fft_size = active_sample_count;
+	fft_size = active_plot_sample_count;
 	onFFT_view_toggled(fft_is_visible);
 
 	updateBufferPreviewer();
@@ -3603,6 +3606,8 @@ void Oscilloscope::onCmbMemoryDepthChanged(QString value)
 		toggle_blockchain_flow(true);
 	}
 	resetStreamingFlag(true);
+	double maxT = (1 << 13) * (1.0 / active_sample_rate) - 1.0 / active_sample_rate * active_plot_sample_count / 2.0;
+	plot.setTimeTriggerInterval(-36E2, maxT);
 }
 
 void Oscilloscope::setSinksDisplayOneBuffer(bool val)
@@ -3654,14 +3659,52 @@ void adiscope::Oscilloscope::onHorizScaleValueChanged(double value)
 
 	ch_ui->cmbMemoryDepth->setCurrentIndex(0);
 	if (timeBase->value() >= TIMEBASE_THRESHOLD) {
-		plot_samples_sequentially = true;
-		if (active_sample_count != -active_trig_sample_count) {
-			active_sample_count = ((-active_trig_sample_count + 3) / 4) * 4;
-			setSinksDisplayOneBuffer(false);
-			plot.setXAxisNumPoints(active_plot_sample_count);
-			resetStreamingFlag(true);
+		plot_samples_sequentially = true;	// streaming
+		const int minKernelBuffers = 4;
+		const int oneBufferMaxSize = 2 * 1024 * 1024; // 2M
+		int m_currentKernelBuffers = minKernelBuffers;
+		if (active_trig_sample_count < 0) {
+			active_sample_count = -active_trig_sample_count;
+			m_currentKernelBuffers = (active_plot_sample_count / active_sample_count) + 1;
+			active_sample_count = (( active_sample_count + 3) / 4) * 4;
+			m_currentKernelBuffers = (m_currentKernelBuffers > MAX_KERNEL_BUFFERS) ? MAX_KERNEL_BUFFERS : m_currentKernelBuffers;
+			m_currentKernelBuffers = (m_currentKernelBuffers < minKernelBuffers) ? minKernelBuffers : m_currentKernelBuffers;
+		} else {			// still streaming but without trigger contraints
+			/* ensure we have the minimum amount of kernel buffers to fit the buffer */
+			while (active_plot_sample_count > (m_currentKernelBuffers * oneBufferMaxSize)
+					&& m_currentKernelBuffers < MAX_KERNEL_BUFFERS) {
+				m_currentKernelBuffers++;
+			}
+
+			/* ensure we don't spend more than 100ms on a acquiring a buffer if we can
+			 * further divide it into smaller buffers */
+			const double maxCaptureDuration = 0.1;
+			while (((static_cast<double>(active_plot_sample_count) / active_sample_rate)
+					/ static_cast<double>(m_currentKernelBuffers)) > maxCaptureDuration
+					&& m_currentKernelBuffers < MAX_KERNEL_BUFFERS) {
+				m_currentKernelBuffers++;
+			}
+			uint64_t chunk_size = active_plot_sample_count / m_currentKernelBuffers;
+			uint64_t chunkSizeBeforeAdjust = chunk_size;
+			chunk_size = 4 * (chunk_size / 4);
+
+			/* If the chunk_size was not divisible by 4 in the first place we would get a smaller value for it. */
+			if (chunk_size + 4 <= oneBufferMaxSize && chunkSizeBeforeAdjust != chunk_size) {
+				chunk_size += 4;
+			}
+
+			// If the buffer size is > 64 * 4M we need to cap the chunk_size to 4M
+			if (chunk_size > oneBufferMaxSize) {
+				chunk_size = oneBufferMaxSize;
+			}
+			active_sample_count = chunk_size;
 		}
+		setSinksDisplayOneBuffer(false);
+		plot.setXAxisNumPoints(active_plot_sample_count);
+		resetStreamingFlag(true);
+		iio->set_kernel_buffer_count(m_currentKernelBuffers);
 	} else {
+		iio->set_kernel_buffer_count();
 		plot_samples_sequentially = false;
 		setSinksDisplayOneBuffer(true);
 		plot.setXAxisNumPoints(0);
@@ -3698,6 +3741,8 @@ void adiscope::Oscilloscope::onHorizScaleValueChanged(double value)
 			timePosition->setValue(-params.timePos);
 	}
 
+	iio->set_device_timeout((active_sample_count / active_sample_rate) * 1000 + 100);
+
 	for (unsigned int i = 0; i < nb_channels; i++) {
 		iio->set_buffer_size(ids[i], active_sample_count);
 		dc_cancel.at(i)->set_buffer_size(active_sample_count);
@@ -3708,10 +3753,6 @@ void adiscope::Oscilloscope::onHorizScaleValueChanged(double value)
 		setDigitalPlotCurvesParams();
 	}
 
-
-	iio->set_device_timeout((active_sample_count / active_sample_rate) * 1000 + 100);
-
-
 	if (started) {
 		iio->unlock();
 	}
@@ -3729,13 +3770,16 @@ void adiscope::Oscilloscope::onHorizScaleValueChanged(double value)
 		power = ceil(log2(active_plot_sample_count));
 	}
 	fft_plot_size = pow(2, power);
-	fft_size = active_sample_count;
+	fft_size = active_plot_sample_count;
 	onFFT_view_toggled(fft_is_visible);
 
 	// Change the sensitivity of time position control
 	timePosition->setStep(value / 10);
 
 	updateBufferPreviewer();
+
+	double maxT = (1 << 13) * (1.0 / active_sample_rate) - 1.0 / active_sample_rate * active_plot_sample_count / 2.0;
+	plot.setTimeTriggerInterval(-36E2, maxT);
 }
 
 bool adiscope::Oscilloscope::gainUpdateNeeded()