fix: resolve 3 deferred issues (STM32-006, STM32-004, FPGA-001)

STM32-006: Remove blocking do-while loop that waited for legacy GUI start
flag — production V7 PyQt GUI never sends it, hanging the MCU at boot.

STM32-004: Check ad9523_init() return code and call Error_Handler() on
failure, matching the pattern used by all other hardware init calls.

FPGA-001: Simplify frame boundary detection to only trigger on
chirp_counter wrap-to-zero. Previous conditions checking == N and == 2N
were unreachable dead code (counter wraps at N-1). Now correct for any
chirps_per_elev value.

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

@@ -175,7 +175,7 @@ float RADAR_Altitude;
 double RADAR_Longitude = 0;
 double RADAR_Latitude = 0;
 
-extern uint8_t GUI_start_flag_received;
+extern uint8_t GUI_start_flag_received;  // [STM32-006] Legacy, unused -- kept for linker compat
 
 
 //RADAR
@@ -1177,7 +1177,14 @@ static int configure_ad9523(void)
 
     // init ad9523 defaults (fills any missing pdata defaults)
     DIAG("CLK", "Calling ad9523_init() -- fills pdata defaults");
-    ad9523_init(&init_param);
+    {
+        int32_t init_ret = ad9523_init(&init_param);
+        DIAG("CLK", "ad9523_init() returned %ld", (long)init_ret);
+        if (init_ret != 0) {
+            DIAG_ERR("CLK", "ad9523_init() FAILED (ret=%ld) -- calling Error_Handler()", (long)init_ret);
+            Error_Handler();
+        }
+    }
 
     /* [Bug #2 FIXED] Removed first ad9523_setup() call that was here.
      * It wrote to the chip while still in reset — writes were lost.
@@ -1800,29 +1807,11 @@ int main(void)
       HAL_UART_Transmit(&huart3, (uint8_t*)gps_send_error, sizeof(gps_send_error) - 1, 1000);
   }
 
-  // Check if start flag was received and settings are ready
+  /* [STM32-006 FIXED] Removed blocking do-while loop that waited for
-  do{
+   * usbHandler.isStartFlagReceived().  The production V7 PyQt GUI does not
-	  if (usbHandler.isStartFlagReceived() &&
+   * send the legacy 4-byte start flag [23,46,158,237], so this loop hung
-		  usbHandler.getState() == USBHandler::USBState::READY_FOR_DATA) {
+   * the MCU at boot indefinitely.  The USB settings handshake (if ever
-
+   * re-enabled) should be handled non-blocking in the main loop. */
-		  const RadarSettings& settings = usbHandler.getSettings();
-
-		  // Use the settings to configure your radar system
-		  /*
-			  settings.getSystemFrequency();
-			  settings.getChirpDuration1();
-			  settings.getChirpDuration2();
-			  settings.getChirpsPerPosition();
-			  settings.getFreqMin();
-			  settings.getFreqMax();
-			  settings.getPRF1();
-			  settings.getPRF2();
-			  settings.getMaxDistance();
-			  */
-
-
-              }
-  }while(!usbHandler.isStartFlagReceived());
 
   /***************************************************************/
   /************RF Power Amplifier Powering up sequence************/

9_Firmware/9_2_FPGA/radar_receiver_final.v

@@ -404,17 +404,15 @@ always @(posedge clk or negedge reset_n) begin
         // Default: no pulse
         new_frame_pulse <= 1'b0;
         
-        // Dynamic frame detection using host_chirps_per_elev.
+        // [FPGA-001 FIXED] Detect frame boundary when chirp_counter wraps to 0.
-        // Detect frame boundary when chirp_counter changes AND is a
+        // The chirp_counter (driven by radar_mode_controller) counts 0..N-1
-        // multiple of host_chirps_per_elev (0, N, 2N, 3N, ...).
+        // and wraps back to 0 at the start of each new frame.  Previous code
-        // Uses a modulo counter that resets at host_chirps_per_elev.
+        // also checked (== host_chirps_per_elev) and (== 2*host_chirps_per_elev)
-        if (chirp_counter != chirp_counter_prev) begin
+        // which were unreachable dead conditions for any N, since the counter
-            if (chirp_counter == 6'd0 ||
+        // never reaches N.  Now works correctly for any chirps_per_elev value.
-                chirp_counter == host_chirps_per_elev ||
+        if (chirp_counter != chirp_counter_prev && chirp_counter == 6'd0) begin
-                chirp_counter == {host_chirps_per_elev, 1'b0}) begin
             new_frame_pulse <= 1'b1;
         end
-        end
         
         // Store previous value
         chirp_counter_prev <= chirp_counter;