Update mock amplifier

cboulay · cboulay · commit 7f102ee2462b · 2026-02-05T21:11:17.000-05:00
diff --git a/Impedance.md b/Impedance.md
@@ -40,36 +40,36 @@ The measurement process uses three amplifier states:
 
 All electrodes actively drive the calibration signal onto the scalp:
 
-| Setting | Value | Description |
-|---------|-------|-------------|
-| All 10K Resistors | OFF | Electrodes not connected to reference |
-| All Drive Signals | ON | All electrodes driving calibration signal |
-| Oscillator Gate | ON | Enable 20 Hz sine wave generator |
-| Calibration Frequency | 20 Hz | Low frequency for skin penetration |
-| Calibration Amplitude | 4095 | Maximum (12-bit DAC) |
-| Wave Shape | Sine (0) | Clean sinusoidal signal |
-| Subject Ground | OFF | Not grounded during measurement |
-| Current Source | OFF | Voltage mode measurement |
+| Setting               | Value    | Description                               |
+|-----------------------|----------|-------------------------------------------|
+| All 10K Resistors     | OFF      | Electrodes not connected to reference     |
+| All Drive Signals     | ON       | All electrodes driving calibration signal |
+| Oscillator Gate       | ON       | Enable 20 Hz sine wave generator          |
+| Calibration Frequency | 20 Hz    | Low frequency for skin penetration        |
+| Calibration Amplitude | 4095     | Maximum (12-bit DAC)                      |
+| Wave Shape            | Sine (0) | Clean sinusoidal signal                   |
+| Subject Ground        | OFF      | Not grounded during measurement           |
+| Current Source        | OFF      | Voltage mode measurement                  |
 
 ### Measurement State (Per-Channel)
 
 For the channel being measured:
 
-| Setting | Value | Description |
-|---------|-------|-------------|
-| Channel Drive Signal | OFF | Stop driving this electrode |
-| Channel 10K Resistor | ON | Connect to reference resistor |
+| Setting              | Value  | Description                   |
+|----------------------|--------|-------------------------------|
+| Channel Drive Signal | OFF    | Stop driving this electrode   |
+| Channel 10K Resistor | ON     | Connect to reference resistor |
 
 All other channels remain in excitation state, creating the voltage divider.
 
 ### Reset State
 
 After measurement, return channel to excitation state:
 
-| Setting | Value | Description |
-|---------|-------|-------------|
-| Channel Drive Signal | ON | Resume driving |
-| Channel 10K Resistor | OFF | Disconnect reference |
+| Setting              | Value  | Description          |
+|----------------------|--------|----------------------|
+| Channel Drive Signal | ON     | Resume driving       |
+| Channel 10K Resistor | OFF    | Disconnect reference |
 
 ## Measurement Algorithm
 
@@ -91,14 +91,12 @@ After measurement, return channel to excitation state:
 
 ## Timing Parameters
 
-From EGI's Net Station implementation:
-
-| Parameter | Value | Description |
-|-----------|-------|-------------|
-| Command Time | 30 ms | Time for command to reach amplifier |
-| Settle Time | 0 ms | Additional settling (Net Station uses 0) |
-| Filter Time | 1.0 s | Duration for filter/measurement |
-| Peak-to-Peak Samples | 51 | Samples for amplitude calculation |
+| Parameter            | Value  | Description                         |
+|----------------------|--------|-------------------------------------|
+| Command Time         | 30 ms  | Time for command to reach amplifier |
+| Settle Time          | 0 ms   | Additional settling                 |
+| Filter Time          | 1.0 s  | Duration for filter/measurement     |
+| Peak-to-Peak Samples | 51     | Samples for amplitude calculation   |
 
 Total time per channel: ~1.03 seconds
 
@@ -142,14 +140,14 @@ Coordinates are on a unit sphere:
 
 ### Key Source Files
 
-| File | Description |
-|------|-------------|
-| [ImpedanceMeasurement.h](src/core/include/egiamp/ImpedanceMeasurement.h) | Class declaration and timing structures |
-| [ImpedanceMeasurement.cpp](src/core/src/ImpedanceMeasurement.cpp) | Measurement algorithm implementation |
-| [LSLStreamer.cpp](src/core/src/LSLStreamer.cpp) | LSL outlet creation with electrode positions |
-| [ElectrodePositions.h](src/core/include/egiamp/ElectrodePositions.h) | Electrode coordinate definitions |
-| [ElectrodePositions.cpp](src/core/src/ElectrodePositions.cpp) | Geodesic position generation |
-| [EGIAmpClient.cpp](src/core/src/EGIAmpClient.cpp) | Integration with streaming client |
+| File                                                                     | Description                                  |
+|--------------------------------------------------------------------------|----------------------------------------------|
+| [ImpedanceMeasurement.h](src/core/include/egiamp/ImpedanceMeasurement.h) | Class declaration and timing structures      |
+| [ImpedanceMeasurement.cpp](src/core/src/ImpedanceMeasurement.cpp)        | Measurement algorithm implementation         |
+| [LSLStreamer.cpp](src/core/src/LSLStreamer.cpp)                          | LSL outlet creation with electrode positions |
+| [ElectrodePositions.h](src/core/include/egiamp/ElectrodePositions.h)     | Electrode coordinate definitions             |
+| [ElectrodePositions.cpp](src/core/src/ElectrodePositions.cpp)            | Geodesic position generation                 |
+| [EGIAmpClient.cpp](src/core/src/EGIAmpClient.cpp)                        | Integration with streaming client            |
 
 ### Key Classes
 
@@ -166,17 +164,17 @@ Coordinates are on a unit sphere:
 
 ### AmpServer Commands
 
-| Command | Description |
-|---------|-------------|
-| `cmd_TurnAll10KOhms` | Set all 10K resistors (0=off, 1=on) |
-| `cmd_TurnAllDriveSignals` | Set all drive signals (0=off, 1=on) |
-| `cmd_TurnChannel10KOhms` | Set single channel 10K resistor |
-| `cmd_TurnChannelDriveSignals` | Set single channel drive signal |
-| `cmd_SetOscillatorGate` | Enable/disable calibration oscillator |
-| `cmd_SetCalibrationSignalFreq` | Set frequency (20 Hz for impedance) |
-| `cmd_SetCalibrationSignalAmplitude` | Set amplitude (0-4095) |
-| `cmd_SetWaveShape` | Set waveform (0=sine, 1=square) |
-| `cmd_DefaultAcquisitionState` | Reset to normal EEG acquisition |
+| Command                             | Description                           |
+|-------------------------------------|---------------------------------------|
+| `cmd_TurnAll10KOhms`                | Set all 10K resistors (0=off, 1=on)   |
+| `cmd_TurnAllDriveSignals`           | Set all drive signals (0=off, 1=on)   |
+| `cmd_TurnChannel10KOhms`            | Set single channel 10K resistor       |
+| `cmd_TurnChannelDriveSignals`       | Set single channel drive signal       |
+| `cmd_SetOscillatorGate`             | Enable/disable calibration oscillator |
+| `cmd_SetCalibrationSignalFreq`      | Set frequency (20 Hz for impedance)   |
+| `cmd_SetCalibrationSignalAmplitude` | Set amplitude (0-4095)                |
+| `cmd_SetWaveShape`                  | Set waveform (0=sine, 1=square)       |
+| `cmd_DefaultAcquisitionState`       | Reset to normal EEG acquisition       |
 
 ## Usage
 
@@ -201,18 +199,6 @@ pip install -r requirements.txt
 python impedance_viewer.py --threshold 50
 ```
 
-## Impedance Thresholds
-
-Recommended thresholds for EGI saline-based nets:
-
-| Quality | Impedance (kΩ) | Color |
-|---------|----------------|-------|
-| Excellent | < 20 | Green |
-| Good | 20 - 50 | Yellow-Green |
-| Acceptable | 50 - 100 | Yellow |
-| Poor | 100 - 200 | Orange |
-| Bad | > 200 | Red |
-
 Values of 1000 kΩ indicate:
 - Electrode not yet measured
 - No contact with scalp
@@ -221,4 +207,5 @@ Values of 1000 kΩ indicate:
 ## References
 
 - EGI AmpServer SDK Documentation
+- Net Station Acquisition source code (NSAAmpSettings.m, ImpedancesController.m)
 - EGI Geodesic Sensor Net Technical Manual
diff --git a/mock/include/MockAmplifier.h b/mock/include/MockAmplifier.h
@@ -165,6 +165,11 @@ class MockAmplifier {
     // For synthetic data generation
     double phase_ = 0.0;
 
+    // DIN counter - cycles 0x0000 to 0xFFFF at 1kHz base rate
+    // At higher sample rates, values are duplicated:
+    // 2kHz = 2x duplicates, 4kHz = 4x, 8kHz = 8x
+    uint32_t dinCounter_ = 0;
+
     int64_t getCurrentTimeMicros() const;
 };
 
diff --git a/mock/src/DataStreamGenerator.cpp b/mock/src/DataStreamGenerator.cpp
@@ -119,9 +119,9 @@ void DataStreamGenerator::stopListening(int64_t ampId) {
 }
 
 void DataStreamGenerator::streamingThread() {
-    const int samplesPerSecond = 1000;  // Base rate
-    const int samplesPerPacket = 5;     // Send 5 samples per network packet
-    const auto packetInterval = std::chrono::milliseconds(samplesPerPacket);
+    // We send packets at ~200 Hz (every 5ms) and adjust samples per packet
+    // based on sample rate to achieve the correct rate
+    const auto packetInterval = std::chrono::milliseconds(5);
 
     while (running_) {
         if (amplifier_->isStreaming() && listening_) {
@@ -153,9 +153,15 @@ void DataStreamGenerator::sendDataToClients() {
 }
 
 void DataStreamGenerator::generateSyntheticData(std::vector<uint8_t>& buffer) {
-    const int samplesPerPacket = 5;
     const auto& state = amplifier_->state();
 
+    // Calculate samples per packet based on sample rate
+    // We send packets every 5ms, so samples = rate * 0.005
+    // 1000 Hz = 5 samples, 2000 Hz = 10 samples, 4000 Hz = 20 samples, 8000 Hz = 40 samples
+    int sampleRate = state.decimatedRate > 0 ? state.decimatedRate : 1000;
+    int samplesPerPacket = (sampleRate * 5) / 1000;
+    if (samplesPerPacket < 1) samplesPerPacket = 1;
+
     // Determine packet format
     if (state.packetFormat == PacketFormat::Format2) {
         // Packet Format 2
diff --git a/mock/src/MockAmplifier.cpp b/mock/src/MockAmplifier.cpp
@@ -369,8 +369,16 @@ void MockAmplifier::generatePacketFormat2(PacketFormat2_SamplePacket& packet) {
     std::lock_guard<std::mutex> lock(mutex_);
     std::memset(&packet, 0, sizeof(packet));
 
-    // Digital inputs (mock value)
-    packet.digitalInputs = 0;
+    // Digital inputs - cycle 0x0000 to 0xFFFF at 1kHz base rate
+    // At higher sample rates, duplicate the values:
+    // 1kHz: each value once, 2kHz: twice, 4kHz: 4x, 8kHz: 8x
+    int sampleRate = state_.decimatedRate > 0 ? state_.decimatedRate : 1000;
+    int duplicateFactor = sampleRate / 1000;
+    if (duplicateFactor < 1) duplicateFactor = 1;
+
+    // Calculate which 1kHz "tick" we're on
+    uint32_t din1kHzTick = static_cast<uint32_t>(state_.packetCounter / duplicateFactor);
+    packet.digitalInputs = static_cast<uint16_t>(din1kHzTick & 0xFFFF);
 
     // TR byte (255 = no GTEN activity)
     packet.tr = state_.gtenTrainRunning ? 251 : 255;
@@ -383,21 +391,62 @@ void MockAmplifier::generatePacketFormat2(PacketFormat2_SamplePacket& packet) {
     packet.netCode = static_cast<uint8_t>(state_.netCode);
 
     // Generate synthetic EEG data
-    double sampleRate = state_.decimatedRate;
     double dt = 1.0 / sampleRate;
     phase_ += dt;
 
     float scaleFactor = getScalingFactor(state_.amplifierType);
 
-    for (int ch = 0; ch < 256; ++ch) {
-        double freq = 10.0 + (ch % 40);
-        double amplitude = 50.0;  // ~50 uV
-        double noise = (rand() % 1000 - 500) / 500.0 * 5.0;
+    // Check if we're in impedance mode (oscillator on, calibration signal configured)
+    bool impedanceMode = state_.oscillatorGate &&
+                         state_.calibrationSignalFreq > 0 &&
+                         state_.calibrationSignalAmplitude > 0;
 
-        if (state_.channelDriveSignals[ch] || state_.allDriveSignals) {
-            freq = state_.calibrationSignalFreq > 0 ? state_.calibrationSignalFreq : 10.0;
-            amplitude = state_.calibrationSignalAmplitude > 0 ?
-                        state_.calibrationSignalAmplitude : 100.0;
+    // Ideal signal amplitude in microvolts for impedance mode
+    // This matches what a 0-ohm electrode would produce
+    constexpr double IDEAL_SIGNAL_UV = 100.0;
+    constexpr double REFERENCE_RESISTOR_KOHMS = 10.0;
+
+    for (int ch = 0; ch < 256; ++ch) {
+        double freq;
+        double amplitude;
+        double noise = (rand() % 1000 - 500) / 500.0 * 2.0;  // ~2 uV noise
+
+        // Check channel state for impedance measurement
+        bool channelDriving = state_.channelDriveSignals[ch] || state_.allDriveSignals;
+        bool channel10K = state_.channel10KOhms[ch] || state_.all10KOhms;
+
+        if (impedanceMode) {
+            // Use calibration signal frequency
+            freq = static_cast<double>(state_.calibrationSignalFreq);
+
+            if (!channelDriving && channel10K) {
+                // Channel is in MEASUREMENT mode (drive off, 10K on)
+                // Simulate voltage divider: amplitude reduced based on "electrode impedance"
+                // Generate a random but stable impedance per channel (5-100 kOhms)
+                double simulatedImpedance = 5.0 + (ch * 17 % 95);  // Deterministic pseudo-random
+
+                // Voltage divider: Vout = Vin * R_ref / (R_ref + Z_electrode)
+                // amplitude = ideal * R_ref / (R_ref + Z)
+                amplitude = IDEAL_SIGNAL_UV * REFERENCE_RESISTOR_KOHMS /
+                           (REFERENCE_RESISTOR_KOHMS + simulatedImpedance);
+            } else if (channelDriving) {
+                // Channel is DRIVING - full calibration signal
+                amplitude = IDEAL_SIGNAL_UV;
+            } else {
+                // Neither driving nor measuring - minimal signal
+                amplitude = 5.0;
+            }
+        } else {
+            // Normal EEG mode - generate synthetic brain signals
+            freq = 10.0 + (ch % 40);  // Different frequencies per channel
+            amplitude = 50.0;  // ~50 uV
+
+            // Add calibration signal if enabled
+            if (channelDriving && state_.calibrationSignalFreq > 0) {
+                freq = static_cast<double>(state_.calibrationSignalFreq);
+                amplitude = state_.calibrationSignalAmplitude > 0 ?
+                            static_cast<double>(state_.calibrationSignalAmplitude) : 100.0;
+            }
         }
 
         double value = amplitude * std::sin(2.0 * M_PI * freq * phase_) + noise;
