fix(pps): align firmware TOW with current RTL

soc/software/pps_python/simulate_pps.py

@@ -298,8 +298,9 @@ def simulate_startup_tow(
     acquisition_ready = rng.uniform(0.0, 18.0, size=(trial_count, len(satellites)))
     complete_subframe_tx = (np.floor(acquisition_ready / 6.0) + 2.0) * 6.0
     # The current hardware validates/delivers the completed subframe only
-    # after receiving eight bits from the following subframe. At 50 bit/s
-    # this is a deterministic 160 ms readout delay (POSTPONE_TOW), distinct
+    # on the ninth following bit because validation reads the old shift
+    # register. At 50 bit/s
+    # this is a deterministic 180 ms readout delay (POSTPONE_TOW), distinct
     # from satellite signal flight time.
     how_interrupt_rx = (
         complete_subframe_tx + POSTPONE_TOW_S + flight_times[None, :]
@@ -354,7 +355,7 @@ def plot_startup_tow(output_dir: Path, startup: dict[str, np.ndarray]) -> None:
         alpha=0.8,
     )
     axes[1, 0].set_xlabel("Phase error [ms]")
-    axes[1, 0].set_title("Provisional: HOW + 160 ms + 68.802 ms")
+    axes[1, 0].set_title("Provisional: HOW + 180 ms + 68.802 ms")
     axes[1, 0].grid(True, alpha=0.3)
 
     axes[1, 1].hist(
@@ -397,7 +398,7 @@ def build_summary(
         f"derived GPS reference RMS error: {finite_rms(timing_error)*1e9:.3f} ns",
         f"capture-to-commit delay mean/p99: {np.mean(latency)*1e3:.3f} / {np.percentile(latency, 99)*1e3:.3f} ms",
         f"first HOW used as receive-now, median phase error: {np.median(startup['how_as_receive_error_s'])*1e3:.3f} ms",
-        f"first HOW + 160 ms + 68.802 ms, median phase error: {np.median(startup['how_plus_pipeline_startoffset_error_s'])*1e3:.3f} ms",
+        f"first HOW + 180 ms + 68.802 ms, median phase error: {np.median(startup['how_plus_pipeline_startoffset_error_s'])*1e3:.3f} ms",
     ]
     for start, stop, label in [
         (0.0, 20.0, "4 satellites"),
@@ -426,10 +427,10 @@ def build_summary(
             "",
             "Interpretation:",
             "- bias/c is millisecond-scale because it contains the 68.802 ms synthetic datum and the minimum satellite path.",
-            "- epoch-aligned TOW (first delivery: HOW + 160 ms) + STARTOFFSET - bias/c reconstructs GPS time at the paired timestamp.",
+            "- epoch-aligned TOW (first delivery: HOW + 180 ms) + STARTOFFSET - bias/c reconstructs GPS time at the paired timestamp.",
             "- treating that old reference as valid at APB arrival converts software latency into PPS phase error.",
             "- timestamping removes that phase misassociation; control application delay remains only as loop delay.",
-            "- baremetal applies the fixed 160 ms readout correction once; the PPS peripheral must not add it again.",
+            "- baremetal applies the fixed 180 ms readout correction once; the PPS peripheral must not add it again.",
         ]
     )
     return "\n".join(lines) + "\n"