merge: resolve conflicts with develop (supersede by PR #89 / #107)

Three conflicts — all resolved in favor of develop, which has a more
refined version of the same work this branch introduced:

- radar_system_top.v: develop's cleaner USB_MODE=1 comment (same value).
- run_regression.sh: develop's ${SYSTEM_RTL[@]} refactor + added
  USB_MODE=1 test variants.
- tb/radar_system_tb.v: develop's ifdef USB_MODE_1 to dump the correct
  USB instance based on mode.

The 400 MHz reset fan-out fix (nco_400m_enhanced, cic_decimator_4x_enhanced,
ddc_400m) and ADAR1000 channel-indexing fix remain intact on this branch.

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

@@ -24,7 +24,6 @@ ADAR1000_AGC::ADAR1000_AGC()
     , saturation_event_count(0)
 {
     memset(cal_offset, 0, sizeof(cal_offset));
-    if (holdoff_frames == 0) holdoff_frames = 1;
 }
 
 // ---------------------------------------------------------------------------

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

@@ -627,7 +627,7 @@ typedef enum {
 
 static SystemError_t last_error = ERROR_NONE;
 static uint32_t error_count = 0;
-static volatile bool system_emergency_state = false;
+static bool system_emergency_state = false;
 
 // Error handler function
 SystemError_t checkSystemHealth(void) {

9_Firmware/9_2_FPGA/rx_gain_control.v

@@ -169,11 +169,11 @@ endfunction
 // =========================================================================
 // Clamp a wider signed value to [-7, +7]
 function signed [3:0] clamp_gain;
-    input signed [5:0] val;  // 6-bit: covers [-22,+22] (max |gain|+step = 7+15)
+    input signed [4:0] val;  // 5-bit to handle overflow from add
     begin
-        if (val > 6'sd7)
+        if (val > 5'sd7)
             clamp_gain = 4'sd7;
-        else if (val < -6'sd7)
+        else if (val < -5'sd7)
             clamp_gain = -4'sd7;
         else
             clamp_gain = val[3:0];
@@ -246,15 +246,15 @@ always @(posedge clk or negedge reset_n) begin
                 // Use inclusive counts/peaks (accounting for simultaneous valid_in)
                 if (wire_frame_sat_incr || frame_sat_count > 8'd0) begin
                     // Clipping detected: reduce gain immediately (attack)
-                    agc_gain <= clamp_gain($signed({agc_gain[3], agc_gain[3], agc_gain}) -
-                                           $signed({2'b00, agc_attack}));
+                    agc_gain <= clamp_gain($signed({agc_gain[3], agc_gain}) -
+                                           $signed({1'b0, agc_attack}));
                     holdoff_counter <= agc_holdoff;  // Reset holdoff
                 end else if ((wire_frame_peak_update ? max_iq[14:7] : frame_peak[14:7])
                              < agc_target) begin
                     // Signal too weak: increase gain after holdoff expires
                     if (holdoff_counter == 4'd0) begin
-                        agc_gain <= clamp_gain($signed({agc_gain[3], agc_gain[3], agc_gain}) +
-                                               $signed({2'b00, agc_decay}));
+                        agc_gain <= clamp_gain($signed({agc_gain[3], agc_gain}) +
+                                               $signed({1'b0, agc_decay}));
                     end else begin
                         holdoff_counter <= holdoff_counter - 4'd1;
                     end

README.md

@@ -7,6 +7,7 @@
 [![Frequency: 10.5GHz](https://img.shields.io/badge/Frequency-10.5GHz-blue)](https://github.com/NawfalMotii79/PLFM_RADAR)
 [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg)](https://github.com/NawfalMotii79/PLFM_RADAR/pulls)
 
+![AERIS-10 Radar System](https://raw.githubusercontent.com/NawfalMotii79/PLFM_RADAR/main/8_Utils/3fb1dabf-2c6d-4b5d-b471-48bc461ce914.jpg)
 
 AERIS-10 is an open-source, low-cost 10.5 GHz phased array radar system featuring Pulse Linear Frequency Modulated (LFM) modulation. Available in two versions (3km and 20km range), it's designed for researchers, drone developers, and serious SDR enthusiasts who want to explore and experiment with phased array radar technology.
 
@@ -46,7 +47,7 @@ The AERIS-10 main sub-systems are:
 
 - **Main Board** containing:
   - **DAC** - Generates the RADAR Chirps
-  - **2x Microwave Mixers (LTC5552)** - For up-conversion and IF-down-conversion
+  - **2x Microwave Mixers (LT5552)** - For up-conversion and IF-down-conversion
   - **4x 4-Channel Phase Shifters (ADAR1000)** - For RX and TX chain beamforming
   - **16x Front End Chips (ADTR1107)** - Used for both Low Noise Amplifying (RX) and Power Amplifying (TX) stages
   - **XC7A50T FPGA** - Handles RADAR Signal Processing on the upstream FTG256 board:
@@ -91,7 +92,7 @@ The AERIS-10 main sub-systems are:
 ### Processing Pipeline
 
 1. **Waveform Generation** - DAC creates LFM chirps
-2. **Up/Down Conversion** - LTC5552 mixers handle frequency translation
+2. **Up/Down Conversion** - LT5552 mixers handle frequency translation
 3. **Beam Steering** - ADAR1000 phase shifters control 16 elements
 4. **Signal Processing (FPGA)**:
    - Raw ADC data capture