feat: AGC phases 4-5 — STM32 outer-loop AGC class + main.cpp integration

Implements the STM32 outer-loop AGC (ADAR1000_AGC) that reads the FPGA
saturation flag on DIG_5/PD13 once per radar frame and adjusts the
ADAR1000 VGA common gain across all 16 RX channels.

Phase 4 — ADAR1000_AGC class (new files):
- ADAR1000_AGC.h/.cpp: attack/recovery/holdoff logic, per-channel
  calibration offsets, effectiveGain() with OOB safety
- test_agc_outer_loop.cpp: 13 tests covering saturation, holdoff,
  recovery, clamping, calibration, SPI spy, reset, mixed sequences

Phase 5 — main.cpp integration:
- Added #include and global outerAgc instance
- AGC update+applyGain call between runRadarPulseSequence() and
  HAL_IWDG_Refresh() in main loop

Build system & shim fixes:
- Makefile: added CXX/CXXFLAGS, C++ object rules, TESTS_WITH_CXX in
  ALL_TESTS (21 total tests)
- stm32_hal_mock.h: const uint8_t* for HAL_UART_Transmit (C++ compat),
  __NOP() macro for host builds
- shims/main.h + real main.h: FPGA_DIG5_SAT pin defines

All tests passing: MCU 21/21, GUI 92/92, cross-layer 29/29.

9_Firmware/9_1_Microcontroller/9_1_1_C_Cpp_Libraries/ADAR1000_AGC.cpp

@@ -0,0 +1,116 @@
+// ADAR1000_AGC.cpp -- STM32 outer-loop AGC implementation
+//
+// See ADAR1000_AGC.h for architecture overview.
+
+#include "ADAR1000_AGC.h"
+#include "ADAR1000_Manager.h"
+#include "diag_log.h"
+
+#include <cstring>
+
+// ---------------------------------------------------------------------------
+// Constructor -- set all config fields to safe defaults
+// ---------------------------------------------------------------------------
+ADAR1000_AGC::ADAR1000_AGC()
+    : agc_base_gain(ADAR1000Manager::kDefaultRxVgaGain) // 30
+    , gain_step_down(4)
+    , gain_step_up(1)
+    , min_gain(0)
+    , max_gain(127)
+    , holdoff_frames(4)
+    , enabled(true)
+    , holdoff_counter(0)
+    , last_saturated(false)
+    , saturation_event_count(0)
+{
+    memset(cal_offset, 0, sizeof(cal_offset));
+}
+
+// ---------------------------------------------------------------------------
+// update -- called once per frame with the FPGA DIG_5 saturation flag
+//
+// Returns true if agc_base_gain changed (caller should then applyGain).
+// ---------------------------------------------------------------------------
+void ADAR1000_AGC::update(bool fpga_saturation)
+{
+    if (!enabled)
+        return;
+
+    last_saturated = fpga_saturation;
+
+    if (fpga_saturation) {
+        // Attack: reduce gain immediately
+        saturation_event_count++;
+        holdoff_counter = 0;
+
+        if (agc_base_gain >= gain_step_down + min_gain) {
+            agc_base_gain -= gain_step_down;
+        } else {
+            agc_base_gain = min_gain;
+        }
+
+        DIAG("AGC", "SAT detected -- gain_base -> %u  (events=%lu)",
+             (unsigned)agc_base_gain, (unsigned long)saturation_event_count);
+
+    } else {
+        // Recovery: wait for holdoff, then increase gain
+        holdoff_counter++;
+
+        if (holdoff_counter >= holdoff_frames) {
+            holdoff_counter = 0;
+
+            if (agc_base_gain + gain_step_up <= max_gain) {
+                agc_base_gain += gain_step_up;
+            } else {
+                agc_base_gain = max_gain;
+            }
+
+            DIAG("AGC", "Recovery step -- gain_base -> %u", (unsigned)agc_base_gain);
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// applyGain -- write effective gain to all 16 RX VGA channels
+//
+// Uses the Manager's adarSetRxVgaGain which takes 1-based channel indices
+// (matching the convention in setBeamAngle).
+// ---------------------------------------------------------------------------
+void ADAR1000_AGC::applyGain(ADAR1000Manager &mgr)
+{
+    for (uint8_t dev = 0; dev < AGC_NUM_DEVICES; ++dev) {
+        for (uint8_t ch = 0; ch < AGC_NUM_CHANNELS; ++ch) {
+            uint8_t gain = effectiveGain(dev * AGC_NUM_CHANNELS + ch);
+            // Channel parameter is 1-based per Manager convention
+            mgr.adarSetRxVgaGain(dev, ch + 1, gain, BROADCAST_OFF);
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// resetState -- clear runtime counters, preserve configuration
+// ---------------------------------------------------------------------------
+void ADAR1000_AGC::resetState()
+{
+    holdoff_counter = 0;
+    last_saturated = false;
+    saturation_event_count = 0;
+}
+
+// ---------------------------------------------------------------------------
+// effectiveGain -- compute clamped per-channel gain
+// ---------------------------------------------------------------------------
+uint8_t ADAR1000_AGC::effectiveGain(uint8_t channel_index) const
+{
+    if (channel_index >= AGC_TOTAL_CHANNELS)
+        return min_gain;  // safety fallback — OOB channels get minimum gain
+
+    int16_t raw = static_cast<int16_t>(agc_base_gain) + cal_offset[channel_index];
+
+    if (raw < static_cast<int16_t>(min_gain))
+        return min_gain;
+    if (raw > static_cast<int16_t>(max_gain))
+        return max_gain;
+
+    return static_cast<uint8_t>(raw);
+}

9_Firmware/9_1_Microcontroller/9_1_1_C_Cpp_Libraries/ADAR1000_AGC.h

@@ -0,0 +1,97 @@
+// ADAR1000_AGC.h -- STM32 outer-loop AGC for ADAR1000 RX VGA gain
+//
+// Adjusts the analog VGA common-mode gain on each ADAR1000 RX channel based on
+// the FPGA's saturation flag (DIG_5 / PD13).  Runs once per radar frame
+// (~258 ms) in the main loop, after runRadarPulseSequence().
+//
+// Architecture:
+//   - Inner loop (FPGA, per-sample): rx_gain_control auto-adjusts digital
+//     gain_shift based on peak magnitude / saturation.  Range ±42 dB.
+//   - Outer loop (THIS MODULE, per-frame): reads FPGA DIG_5 GPIO.  If
+//     saturation detected, reduces agc_base_gain immediately (attack).  If no
+//     saturation for holdoff_frames, increases agc_base_gain (decay/recovery).
+//
+// Per-channel gain formula:
+//   VGA[dev][ch] = clamp(agc_base_gain + cal_offset[dev*4+ch], min_gain, max_gain)
+//
+// The cal_offset array allows per-element calibration to correct inter-channel
+// gain imbalance.  Default is all zeros (uniform gain).
+
+#ifndef ADAR1000_AGC_H
+#define ADAR1000_AGC_H
+
+#include <stdint.h>
+
+// Forward-declare to avoid pulling in the full ADAR1000_Manager header here.
+// The .cpp includes the real header.
+class ADAR1000Manager;
+
+// Number of ADAR1000 devices
+#define AGC_NUM_DEVICES   4
+// Number of channels per ADAR1000
+#define AGC_NUM_CHANNELS  4
+// Total RX channels
+#define AGC_TOTAL_CHANNELS (AGC_NUM_DEVICES * AGC_NUM_CHANNELS)
+
+class ADAR1000_AGC {
+public:
+    // --- Configuration (public for easy field-testing / GUI override) ---
+
+    // Common-mode base gain (raw ADAR1000 register value, 0-255).
+    // Default matches ADAR1000Manager::kDefaultRxVgaGain = 30.
+    uint8_t agc_base_gain;
+
+    // Per-channel calibration offset (signed, added to agc_base_gain).
+    // Index = device*4 + channel.  Default: all 0.
+    int8_t cal_offset[AGC_TOTAL_CHANNELS];
+
+    // How much to decrease agc_base_gain per frame when saturated (attack).
+    uint8_t gain_step_down;
+
+    // How much to increase agc_base_gain per frame when recovering (decay).
+    uint8_t gain_step_up;
+
+    // Minimum allowed agc_base_gain (floor).
+    uint8_t min_gain;
+
+    // Maximum allowed agc_base_gain (ceiling).
+    uint8_t max_gain;
+
+    // Number of consecutive non-saturated frames required before gain-up.
+    uint8_t holdoff_frames;
+
+    // Master enable.  When false, update() is a no-op.
+    bool enabled;
+
+    // --- Runtime state (read-only for diagnostics) ---
+
+    // Consecutive non-saturated frame counter (resets on saturation).
+    uint8_t holdoff_counter;
+
+    // True if the last update() saw saturation.
+    bool last_saturated;
+
+    // Total saturation events since reset/construction.
+    uint32_t saturation_event_count;
+
+    // --- Methods ---
+
+    ADAR1000_AGC();
+
+    // Call once per frame after runRadarPulseSequence().
+    // fpga_saturation: result of HAL_GPIO_ReadPin(GPIOD, GPIO_PIN_13) == GPIO_PIN_SET
+    void update(bool fpga_saturation);
+
+    // Apply the current gain to all 16 RX VGA channels via the Manager.
+    void applyGain(ADAR1000Manager &mgr);
+
+    // Reset runtime state (holdoff counter, saturation count) without
+    // changing configuration.
+    void resetState();
+
+    // Compute the effective gain for a specific channel index (0-15),
+    // clamped to [min_gain, max_gain].  Useful for diagnostics.
+    uint8_t effectiveGain(uint8_t channel_index) const;
+};
+
+#endif // ADAR1000_AGC_H

9_Firmware/9_1_Microcontroller/9_1_3_C_Cpp_Code/main.cpp

@@ -23,6 +23,7 @@
 #include "usbd_cdc_if.h"
 #include "adar1000.h"
 #include "ADAR1000_Manager.h"
+#include "ADAR1000_AGC.h"
 extern "C" {
 #include "ad9523.h"
 }
@@ -224,6 +225,7 @@ extern SPI_HandleTypeDef hspi4;
 //ADAR1000
 
 ADAR1000Manager adarManager;
+ADAR1000_AGC    outerAgc;
 static uint8_t matrix1[15][16];
 static uint8_t matrix2[15][16];
 static uint8_t vector_0[16] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
@@ -2114,6 +2116,15 @@ int main(void)
 
       runRadarPulseSequence();
 
+      /* [AGC] Outer-loop AGC: read FPGA saturation flag (DIG_5 / PD13),
+       * adjust ADAR1000 VGA common gain once per radar frame (~258 ms). */
+      {
+          bool sat = HAL_GPIO_ReadPin(FPGA_DIG5_SAT_GPIO_Port,
+                                      FPGA_DIG5_SAT_Pin) == GPIO_PIN_SET;
+          outerAgc.update(sat);
+          outerAgc.applyGain(adarManager);
+      }
+
       /* [GAP-3 FIX 2] Kick hardware watchdog — if we don't reach here within
        * ~4 s, the IWDG resets the MCU automatically. */
       HAL_IWDG_Refresh(&hiwdg);

9_Firmware/9_1_Microcontroller/9_1_3_C_Cpp_Code/main.h

@@ -141,6 +141,15 @@ void Error_Handler(void);
 #define EN_DIS_RFPA_VDD_GPIO_Port GPIOD
 #define EN_DIS_COOLING_Pin GPIO_PIN_7
 #define EN_DIS_COOLING_GPIO_Port GPIOD
+
+/* FPGA digital I/O (directly connected GPIOs) */
+#define FPGA_DIG5_SAT_Pin       GPIO_PIN_13
+#define FPGA_DIG5_SAT_GPIO_Port GPIOD
+#define FPGA_DIG6_Pin           GPIO_PIN_14
+#define FPGA_DIG6_GPIO_Port     GPIOD
+#define FPGA_DIG7_Pin           GPIO_PIN_15
+#define FPGA_DIG7_GPIO_Port     GPIOD
+
 #define ADF4382_RX_CE_Pin GPIO_PIN_9
 #define ADF4382_RX_CE_GPIO_Port GPIOG
 #define ADF4382_RX_CS_Pin GPIO_PIN_10

9_Firmware/9_1_Microcontroller/tests/Makefile

@@ -16,10 +16,17 @@
 ################################################################################
 
 CC       := cc
+CXX      := c++
 CFLAGS   := -std=c11 -Wall -Wextra -Wno-unused-parameter -g -O0
+CXXFLAGS := -std=c++17 -Wall -Wextra -Wno-unused-parameter -g -O0
 # Shim headers come FIRST so they override real headers
 INCLUDES := -Ishims -I. -I../9_1_1_C_Cpp_Libraries
 
+# C++ library directory (AGC, ADAR1000 Manager)
+CXX_LIB_DIR := ../9_1_1_C_Cpp_Libraries
+CXX_SRCS    := $(CXX_LIB_DIR)/ADAR1000_AGC.cpp $(CXX_LIB_DIR)/ADAR1000_Manager.cpp
+CXX_OBJS    := ADAR1000_AGC.o ADAR1000_Manager.o
+
 # Real source files compiled against mock headers
 REAL_SRC := ../9_1_1_C_Cpp_Libraries/adf4382a_manager.c
 
@@ -62,7 +69,10 @@ TESTS_STANDALONE := test_bug12_pa_cal_loop_inverted \
 # Tests that need platform_noos_stm32.o + mocks
 TESTS_WITH_PLATFORM := test_bug11_platform_spi_transmit_only
 
-ALL_TESTS := $(TESTS_WITH_REAL) $(TESTS_MOCK_ONLY) $(TESTS_STANDALONE) $(TESTS_WITH_PLATFORM)
+# C++ tests (AGC outer loop)
+TESTS_WITH_CXX := test_agc_outer_loop
+
+ALL_TESTS := $(TESTS_WITH_REAL) $(TESTS_MOCK_ONLY) $(TESTS_STANDALONE) $(TESTS_WITH_PLATFORM) $(TESTS_WITH_CXX)
 
 .PHONY: all build test clean \
         $(addprefix test_,bug1 bug2 bug3 bug4 bug5 bug6 bug7 bug8 bug9 bug10 bug11 bug12 bug13 bug14 bug15) \
@@ -156,6 +166,24 @@ test_gap3_emergency_state_ordering: test_gap3_emergency_state_ordering.c
 $(TESTS_WITH_PLATFORM): %: %.c $(MOCK_OBJS) $(PLATFORM_OBJ)
 	$(CC) $(CFLAGS) $(INCLUDES) $< $(MOCK_OBJS) $(PLATFORM_OBJ) -o $@
 
+# --- C++ object rules ---
+
+ADAR1000_AGC.o: $(CXX_LIB_DIR)/ADAR1000_AGC.cpp $(CXX_LIB_DIR)/ADAR1000_AGC.h
+	$(CXX) $(CXXFLAGS) $(INCLUDES) -c $< -o $@
+
+ADAR1000_Manager.o: $(CXX_LIB_DIR)/ADAR1000_Manager.cpp $(CXX_LIB_DIR)/ADAR1000_Manager.h
+	$(CXX) $(CXXFLAGS) $(INCLUDES) -c $< -o $@
+
+# --- C++ test binary rules ---
+
+test_agc_outer_loop: test_agc_outer_loop.cpp $(CXX_OBJS) $(MOCK_OBJS)
+	$(CXX) $(CXXFLAGS) $(INCLUDES) $< $(CXX_OBJS) $(MOCK_OBJS) -o $@
+
+# Convenience target
+.PHONY: test_agc
+test_agc: test_agc_outer_loop
+	./test_agc_outer_loop
+
 # --- Individual test targets ---
 
 test_bug1: test_bug1_timed_sync_init_ordering

9_Firmware/9_1_Microcontroller/tests/shims/main.h

@@ -129,6 +129,14 @@ void Error_Handler(void);
 #define GYR_INT_Pin GPIO_PIN_8
 #define GYR_INT_GPIO_Port GPIOC
 
+/* FPGA digital I/O (directly connected GPIOs) */
+#define FPGA_DIG5_SAT_Pin       GPIO_PIN_13
+#define FPGA_DIG5_SAT_GPIO_Port GPIOD
+#define FPGA_DIG6_Pin           GPIO_PIN_14
+#define FPGA_DIG6_GPIO_Port     GPIOD
+#define FPGA_DIG7_Pin           GPIO_PIN_15
+#define FPGA_DIG7_GPIO_Port     GPIOD
+
 #ifdef __cplusplus
 }
 #endif

9_Firmware/9_1_Microcontroller/tests/stm32_hal_mock.c

@@ -175,7 +175,7 @@ void HAL_Delay(uint32_t Delay)
     mock_tick += Delay;
 }
 
-HAL_StatusTypeDef HAL_UART_Transmit(UART_HandleTypeDef *huart, uint8_t *pData,
+HAL_StatusTypeDef HAL_UART_Transmit(UART_HandleTypeDef *huart, const uint8_t *pData,
                                      uint16_t Size, uint32_t Timeout)
 {
     spy_push((SpyRecord){

9_Firmware/9_1_Microcontroller/tests/stm32_hal_mock.h

@@ -34,6 +34,10 @@ typedef uint32_t HAL_StatusTypeDef;
 
 #define HAL_MAX_DELAY 0xFFFFFFFFU
 
+#ifndef __NOP
+#define __NOP() ((void)0)
+#endif
+
 /* ========================= GPIO Types ============================ */
 
 typedef struct {
@@ -182,7 +186,7 @@ GPIO_PinState HAL_GPIO_ReadPin(GPIO_TypeDef *GPIOx, uint16_t GPIO_Pin);
 void          HAL_GPIO_TogglePin(GPIO_TypeDef *GPIOx, uint16_t GPIO_Pin);
 uint32_t      HAL_GetTick(void);
 void          HAL_Delay(uint32_t Delay);
-HAL_StatusTypeDef HAL_UART_Transmit(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint32_t Timeout);
+HAL_StatusTypeDef HAL_UART_Transmit(UART_HandleTypeDef *huart, const uint8_t *pData, uint16_t Size, uint32_t Timeout);
 
 /* ========================= SPI stubs ============================== */
 

9_Firmware/9_1_Microcontroller/tests/test_agc_outer_loop.cpp

@@ -0,0 +1,361 @@
+// test_agc_outer_loop.cpp -- C++ unit tests for ADAR1000_AGC outer-loop AGC
+//
+// Tests the STM32 outer-loop AGC class that adjusts ADAR1000 VGA gain based
+// on the FPGA's saturation flag.  Uses the existing HAL mock/spy framework.
+//
+// Build: c++ -std=c++17 ... (see Makefile TESTS_WITH_CXX rule)
+
+#include <cassert>
+#include <cstdio>
+#include <cstring>
+
+// Shim headers override real STM32/diag headers
+#include "stm32_hal_mock.h"
+#include "ADAR1000_AGC.h"
+#include "ADAR1000_Manager.h"
+
+// ---------------------------------------------------------------------------
+// Linker symbols required by ADAR1000_Manager.cpp (pulled in via main.h shim)
+// ---------------------------------------------------------------------------
+uint8_t GUI_start_flag_received = 0;
+uint8_t USB_Buffer[64] = {0};
+extern "C" void Error_Handler(void) {}
+
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+
+static int tests_passed = 0;
+static int tests_total  = 0;
+
+#define RUN_TEST(fn)                                                           \
+    do {                                                                        \
+        tests_total++;                                                          \
+        printf("  [%2d] %-55s ", tests_total, #fn);                            \
+        fn();                                                                   \
+        tests_passed++;                                                         \
+        printf("PASS\n");                                                       \
+    } while (0)
+
+// ---------------------------------------------------------------------------
+// Test 1: Default construction matches design spec
+// ---------------------------------------------------------------------------
+static void test_defaults()
+{
+    ADAR1000_AGC agc;
+
+    assert(agc.agc_base_gain == 30);  // kDefaultRxVgaGain
+    assert(agc.gain_step_down == 4);
+    assert(agc.gain_step_up == 1);
+    assert(agc.min_gain == 0);
+    assert(agc.max_gain == 127);
+    assert(agc.holdoff_frames == 4);
+    assert(agc.enabled == true);
+    assert(agc.holdoff_counter == 0);
+    assert(agc.last_saturated == false);
+    assert(agc.saturation_event_count == 0);
+
+    // All cal offsets zero
+    for (int i = 0; i < AGC_TOTAL_CHANNELS; ++i) {
+        assert(agc.cal_offset[i] == 0);
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Test 2: Saturation reduces gain by step_down
+// ---------------------------------------------------------------------------
+static void test_saturation_reduces_gain()
+{
+    ADAR1000_AGC agc;
+    uint8_t initial = agc.agc_base_gain;  // 30
+
+    agc.update(true);  // saturation
+
+    assert(agc.agc_base_gain == initial - agc.gain_step_down);  // 26
+    assert(agc.last_saturated == true);
+    assert(agc.holdoff_counter == 0);
+}
+
+// ---------------------------------------------------------------------------
+// Test 3: Holdoff prevents premature gain-up
+// ---------------------------------------------------------------------------
+static void test_holdoff_prevents_early_gain_up()
+{
+    ADAR1000_AGC agc;
+    agc.update(true);  // saturate once -> gain = 26
+    uint8_t after_sat = agc.agc_base_gain;
+
+    // Feed (holdoff_frames - 1) clear frames — should NOT increase gain
+    for (uint8_t i = 0; i < agc.holdoff_frames - 1; ++i) {
+        agc.update(false);
+        assert(agc.agc_base_gain == after_sat);
+    }
+
+    // holdoff_counter should be holdoff_frames - 1
+    assert(agc.holdoff_counter == agc.holdoff_frames - 1);
+}
+
+// ---------------------------------------------------------------------------
+// Test 4: Recovery after holdoff period
+// ---------------------------------------------------------------------------
+static void test_recovery_after_holdoff()
+{
+    ADAR1000_AGC agc;
+    agc.update(true);  // saturate -> gain = 26
+    uint8_t after_sat = agc.agc_base_gain;
+
+    // Feed exactly holdoff_frames clear frames
+    for (uint8_t i = 0; i < agc.holdoff_frames; ++i) {
+        agc.update(false);
+    }
+
+    assert(agc.agc_base_gain == after_sat + agc.gain_step_up);  // 27
+    assert(agc.holdoff_counter == 0);  // reset after recovery
+}
+
+// ---------------------------------------------------------------------------
+// Test 5: Min gain clamping
+// ---------------------------------------------------------------------------
+static void test_min_gain_clamp()
+{
+    ADAR1000_AGC agc;
+    agc.min_gain = 10;
+    agc.agc_base_gain = 12;
+    agc.gain_step_down = 4;
+
+    agc.update(true);  // 12 - 4 = 8, but min = 10
+    assert(agc.agc_base_gain == 10);
+
+    agc.update(true);  // already at min
+    assert(agc.agc_base_gain == 10);
+}
+
+// ---------------------------------------------------------------------------
+// Test 6: Max gain clamping
+// ---------------------------------------------------------------------------
+static void test_max_gain_clamp()
+{
+    ADAR1000_AGC agc;
+    agc.max_gain = 32;
+    agc.agc_base_gain = 31;
+    agc.gain_step_up = 2;
+    agc.holdoff_frames = 1;  // immediate recovery
+
+    agc.update(false);  // 31 + 2 = 33, but max = 32
+    assert(agc.agc_base_gain == 32);
+
+    agc.update(false);  // already at max
+    assert(agc.agc_base_gain == 32);
+}
+
+// ---------------------------------------------------------------------------
+// Test 7: Per-channel calibration offsets
+// ---------------------------------------------------------------------------
+static void test_calibration_offsets()
+{
+    ADAR1000_AGC agc;
+    agc.agc_base_gain = 30;
+    agc.min_gain = 0;
+    agc.max_gain = 60;
+
+    agc.cal_offset[0]  =  5;   // 30 + 5  = 35
+    agc.cal_offset[1]  = -10;  // 30 - 10 = 20
+    agc.cal_offset[15] =  40;  // 30 + 40 = 60 (clamped to max)
+
+    assert(agc.effectiveGain(0) == 35);
+    assert(agc.effectiveGain(1) == 20);
+    assert(agc.effectiveGain(15) == 60);  // clamped to max_gain
+
+    // Negative clamp
+    agc.cal_offset[2] = -50;   // 30 - 50 = -20, clamped to min_gain = 0
+    assert(agc.effectiveGain(2) == 0);
+
+    // Out-of-range index returns min_gain
+    assert(agc.effectiveGain(16) == agc.min_gain);
+}
+
+// ---------------------------------------------------------------------------
+// Test 8: Disabled AGC is a no-op
+// ---------------------------------------------------------------------------
+static void test_disabled_noop()
+{
+    ADAR1000_AGC agc;
+    agc.enabled = false;
+    uint8_t original = agc.agc_base_gain;
+
+    agc.update(true);   // should be ignored
+    assert(agc.agc_base_gain == original);
+    assert(agc.last_saturated == false);  // not updated when disabled
+    assert(agc.saturation_event_count == 0);
+
+    agc.update(false);  // also ignored
+    assert(agc.agc_base_gain == original);
+}
+
+// ---------------------------------------------------------------------------
+// Test 9: applyGain() produces correct SPI writes
+// ---------------------------------------------------------------------------
+static void test_apply_gain_spi()
+{
+    spy_reset();
+
+    ADAR1000Manager mgr;  // creates 4 devices
+    ADAR1000_AGC agc;
+    agc.agc_base_gain = 42;
+
+    agc.applyGain(mgr);
+
+    // Each channel: adarSetRxVgaGain -> adarWrite(gain) + adarWrite(LOAD_WORKING)
+    // Each adarWrite: CS_low (GPIO_WRITE) + SPI_TRANSMIT + CS_high (GPIO_WRITE)
+    // = 3 spy records per adarWrite
+    // = 6 spy records per channel
+    // = 16 channels * 6 = 96 total spy records
+
+    // Verify SPI transmit count: 2 SPI calls per channel * 16 channels = 32
+    int spi_count = spy_count_type(SPY_SPI_TRANSMIT);
+    assert(spi_count == 32);
+
+    // Verify GPIO write count: 4 GPIO writes per channel (CS low + CS high for each of 2 adarWrite calls)
+    int gpio_writes = spy_count_type(SPY_GPIO_WRITE);
+    assert(gpio_writes == 64);  // 16 ch * 2 adarWrite * 2 GPIO each
+}
+
+// ---------------------------------------------------------------------------
+// Test 10: resetState() clears counters but preserves config
+// ---------------------------------------------------------------------------
+static void test_reset_preserves_config()
+{
+    ADAR1000_AGC agc;
+    agc.agc_base_gain = 42;
+    agc.gain_step_down = 8;
+    agc.cal_offset[3] = -5;
+
+    // Generate some state
+    agc.update(true);
+    agc.update(true);
+    assert(agc.saturation_event_count == 2);
+    assert(agc.last_saturated == true);
+
+    agc.resetState();
+
+    // State cleared
+    assert(agc.holdoff_counter == 0);
+    assert(agc.last_saturated == false);
+    assert(agc.saturation_event_count == 0);
+
+    // Config preserved
+    assert(agc.agc_base_gain == 42 - 8 - 8);  // two saturations applied before reset
+    assert(agc.gain_step_down == 8);
+    assert(agc.cal_offset[3] == -5);
+}
+
+// ---------------------------------------------------------------------------
+// Test 11: Saturation counter increments correctly
+// ---------------------------------------------------------------------------
+static void test_saturation_counter()
+{
+    ADAR1000_AGC agc;
+
+    for (int i = 0; i < 10; ++i) {
+        agc.update(true);
+    }
+    assert(agc.saturation_event_count == 10);
+
+    // Clear frames don't increment saturation count
+    for (int i = 0; i < 5; ++i) {
+        agc.update(false);
+    }
+    assert(agc.saturation_event_count == 10);
+}
+
+// ---------------------------------------------------------------------------
+// Test 12: Mixed saturation/clear sequence
+// ---------------------------------------------------------------------------
+static void test_mixed_sequence()
+{
+    ADAR1000_AGC agc;
+    agc.agc_base_gain = 30;
+    agc.gain_step_down = 4;
+    agc.gain_step_up = 1;
+    agc.holdoff_frames = 3;
+
+    // Saturate: 30 -> 26
+    agc.update(true);
+    assert(agc.agc_base_gain == 26);
+    assert(agc.holdoff_counter == 0);
+
+    // 2 clear frames (not enough for recovery)
+    agc.update(false);
+    agc.update(false);
+    assert(agc.agc_base_gain == 26);
+    assert(agc.holdoff_counter == 2);
+
+    // Saturate again: 26 -> 22, counter resets
+    agc.update(true);
+    assert(agc.agc_base_gain == 22);
+    assert(agc.holdoff_counter == 0);
+    assert(agc.saturation_event_count == 2);
+
+    // 3 clear frames -> recovery: 22 -> 23
+    agc.update(false);
+    agc.update(false);
+    agc.update(false);
+    assert(agc.agc_base_gain == 23);
+    assert(agc.holdoff_counter == 0);
+
+    // 3 more clear -> 23 -> 24
+    agc.update(false);
+    agc.update(false);
+    agc.update(false);
+    assert(agc.agc_base_gain == 24);
+}
+
+// ---------------------------------------------------------------------------
+// Test 13: Effective gain with edge-case base_gain values
+// ---------------------------------------------------------------------------
+static void test_effective_gain_edge_cases()
+{
+    ADAR1000_AGC agc;
+    agc.min_gain = 5;
+    agc.max_gain = 250;
+
+    // Base gain at zero with positive offset
+    agc.agc_base_gain = 0;
+    agc.cal_offset[0] = 3;
+    assert(agc.effectiveGain(0) == 5);  // 0 + 3 = 3, clamped to min_gain=5
+
+    // Base gain at max with zero offset
+    agc.agc_base_gain = 250;
+    agc.cal_offset[0] = 0;
+    assert(agc.effectiveGain(0) == 250);
+
+    // Base gain at max with positive offset -> clamped
+    agc.agc_base_gain = 250;
+    agc.cal_offset[0] = 10;
+    assert(agc.effectiveGain(0) == 250);  // clamped to max_gain
+}
+
+// ---------------------------------------------------------------------------
+// main
+// ---------------------------------------------------------------------------
+int main()
+{
+    printf("=== ADAR1000_AGC Outer-Loop Unit Tests ===\n");
+
+    RUN_TEST(test_defaults);
+    RUN_TEST(test_saturation_reduces_gain);
+    RUN_TEST(test_holdoff_prevents_early_gain_up);
+    RUN_TEST(test_recovery_after_holdoff);
+    RUN_TEST(test_min_gain_clamp);
+    RUN_TEST(test_max_gain_clamp);
+    RUN_TEST(test_calibration_offsets);
+    RUN_TEST(test_disabled_noop);
+    RUN_TEST(test_apply_gain_spi);
+    RUN_TEST(test_reset_preserves_config);
+    RUN_TEST(test_saturation_counter);
+    RUN_TEST(test_mixed_sequence);
+    RUN_TEST(test_effective_gain_edge_cases);
+
+    printf("=== Results: %d/%d passed ===\n", tests_passed, tests_total);
+    return (tests_passed == tests_total) ? 0 : 1;
+}