fix(mcu): PR-AB.a — move vector_0 out of inner beam_pos loop

runRadarPulseSequence used to fire vector_0 (broadside reference)
between every matrix1 and matrix2 pattern, i.e. 15 times per azimuth.
That dwell × 8 ms × 15 = 120 ms per azimuth × 50 azimuths = ~6 s of
the 18.4 s revisit time was burned on redundant broadside frames.

Pull vector_0 out of the loop and fire it once per azimuth before the
sweep. Each azimuth now produces 1 broadside frame + 30 steered frames
(matrix1 + matrix2 across 15 beam_pos), down from 15 + 30 = 45 frames.
Revisit time drops from 18.4 s to ~12.8 s (31% improvement).

If multiple per-position broadside frames are ever needed, gate them
behind a runtime switch — the comment block flags this.

test_bug16_runradar_shadows_globals updated to mirror the new
1-outside + 2-inside m-counter pattern; 13/13 PASS, full MCU
regression 51/0 + 34/0.

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

@@ -567,12 +567,15 @@ void runRadarPulseSequence() {
     // BeamPos/Azimuth/ChirpCount. Local declarations would shadow them and
     // freeze the telemetry at 1.
 
-    /* Main beam steering sequence. Per beam position we push three ADAR1000
+    /* Main beam steering sequence. Per azimuth slot we fire one broadside
-     * pattern updates: matrix1, vector_0 (broadside), matrix2 (see
+     * reference (vector_0) and then sweep 15 beam positions, each firing
-     * initializeBeamMatrices for the actual sim-peak directions and the
+     * matrix1 (negative-θ scan) and matrix2 (positive-θ scan). PR-AB.a
-     * sign-convention caveat). The FPGA's chirp_scheduler is firing the
+     * pulled vector_0 out of the inner loop — previously fired 15× per
-     * 3-PRI ladder against whichever pattern is currently loaded; we hold
+     * azimuth (between every matrix1/matrix2 pair) which dominated the
-     * each pattern for one full SHORT/MEDIUM/LONG ladder before advancing.
+     * 18.4 s revisit time without serving a documented per-pos purpose.
+     * One broadside frame per azimuth is sufficient as a clutter
+     * reference; if multiple per-pos broadside frames are ever needed
+     * they should re-enter behind a runtime switch.
      *
      * Per-pattern dwell:
      *   16 × PRI_SHORT  (175 us) +
@@ -581,26 +584,30 @@ void runRadarPulseSequence() {
      * HAL_Delay yields to SysTick / IRQs, so unlike the removed
      * executeChirpSequence busy-loop the MCU stays responsive to USB CDC,
      * UART, and I2C peripherals during the dwell. For drift-immune sync
-     * we'd wait on an FPGA `subframe_pulse` GPIO instead, but the bitstream
+     * we'd wait on an FPGA `subframe_pulse` GPIO instead — DIG_7
-     * does not currently bring that signal out to a pin. */
+     * (H12→PD15) is wired in the schematic but currently driven by the
+     * F-6.4 watchdog OR; reassigning it is a tracked follow-up
+     * (PR-AB.b). */
     static const uint32_t BEAM_PATTERN_DWELL_MS = 8u;
 
+    // One broadside (vector_0) reference frame per azimuth — replaces the
+    // 15 in-loop fires that PR-AB.a removed.
+    DIAG("SYS", "Broadside reference (vector_0) — 1× per azimuth");
+    adarManager.setCustomBeamPattern16(vector_0, ADAR1000Manager::BeamDirection::TX);
+    adarManager.setCustomBeamPattern16(vector_0, ADAR1000Manager::BeamDirection::RX);
+    HAL_Delay(BEAM_PATTERN_DWELL_MS);
+    m += m_max/2;
+
     for(int beam_pos = 0; beam_pos < 15; beam_pos++) {
     	HAL_GPIO_TogglePin(GPIOD, GPIO_PIN_9);// new_elevation -- mode 2'b00 input only; no-op in production mode 2'b01 but harmless to keep
-    	DIAG("SYS", "Beam pos %d/15: patterns matrix1/vector_0/matrix2", beam_pos);
+    	DIAG("SYS", "Beam pos %d/15: patterns matrix1/matrix2", beam_pos);
-        // Pattern 1: matrix1
+        // Pattern 1: matrix1 (negative-θ scan, peak at -62°..-3°)
         adarManager.setCustomBeamPattern16(matrix1[beam_pos], ADAR1000Manager::BeamDirection::TX);
         adarManager.setCustomBeamPattern16(matrix1[beam_pos], ADAR1000Manager::BeamDirection::RX);
         HAL_Delay(BEAM_PATTERN_DWELL_MS);
         m += m_max/2;
 
-        // Pattern 2: vector_0 (broadside)
+        // Pattern 2: matrix2 (positive-θ scan, peak at +3°..+62°)
-        adarManager.setCustomBeamPattern16(vector_0, ADAR1000Manager::BeamDirection::TX);
-        adarManager.setCustomBeamPattern16(vector_0, ADAR1000Manager::BeamDirection::RX);
-        HAL_Delay(BEAM_PATTERN_DWELL_MS);
-        m += m_max/2;
-
-        // Pattern 3: matrix2
         adarManager.setCustomBeamPattern16(matrix2[beam_pos], ADAR1000Manager::BeamDirection::TX);
         adarManager.setCustomBeamPattern16(matrix2[beam_pos], ADAR1000Manager::BeamDirection::RX);
         HAL_Delay(BEAM_PATTERN_DWELL_MS);

9_Firmware/9_1_Microcontroller/tests/test_bug16_runradar_shadows_globals.c

@@ -59,13 +59,20 @@ static void run_buggy(void)
     (void)m; (void)n; (void)y;
 }
 
-/* Post-fix: same body, no local redeclaration — references globals. */
+/* Post-fix: same body, no local redeclaration — references globals.
+ * PR-AB.a moved vector_0 out of the inner loop, so the m advance is now
+ *   1 (vector_0, before loop) + 2 × 15 (matrix1+matrix2 in loop) = 31 increments
+ * per azimuth, instead of the prior 3 × 15 = 45. The wrap behavior
+ * (g_m wraps on every iteration's matrix2 add) is unchanged. */
 static void run_fixed(void)
 {
+    /* PR-AB.a: vector_0 broadside reference, 1× per azimuth (was inside loop). */
+    g_m += m_max / 2;
+    if (g_m > m_max) g_m = 1;
+
     for (int beam_pos = 0; beam_pos < 15; beam_pos++) {
-        g_m += m_max / 2;
+        g_m += m_max / 2;  /* matrix1 (negative-θ scan) */
-        g_m += m_max / 2;
+        g_m += m_max / 2;  /* matrix2 (positive-θ scan) */
-        g_m += m_max / 2;
         if (g_m > m_max) g_m = 1;
 
         g_n++;