fix(panda): wait for the late replayed PULSE train after a parameter change

The PULSE blocks replay a full train ~0.3-0.6 s after a parameter write, without a
trigger. configure_line returned after 50 ms, so the train ran into the first line and
blocked its trigger (line counter 0). Now both PULSE outputs must stay low for
PARAM_QUIET_TIME (1 s); only on a parameter change, i.e. once per scan.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01M8zoDyJxbBLmjZCEPUo5FM

csaxs_bec/devices/aerotech/README.md

@@ -165,5 +165,6 @@ edges.
 PandA FPGA 4.1 PULSE block: an ENABLE edge, a parameter write or a dropped trigger often
 makes it replay the previous pulse train without a trigger. The device keeps the PULSE
 blocks enabled, writes their parameters only when they change (once per scan) and then waits
-until such a train is over (pulses can appear on TTLOUT2/3 meanwhile), and the trigger path
+until such a train is over (pulses can appear on TTLOUT2/3 meanwhile; the train starts only
+~0.3-0.6 s after the write, so both outputs must stay low for 1 s), and the trigger path
 filters out edges during a line, so no trigger is ever dropped by a PULSE block.

csaxs_bec/devices/panda_box/panda_line_trigger.py

@@ -22,7 +22,9 @@ any trigger. With unchanged parameters and ENABLE kept high, hundreds of trigger
 a row were correct. So the PULSE blocks stay enabled, their parameters are only written
 when they change (once per scan), followed by a wait until a replayed train is over, and
 edges during a line are filtered out before the PULSE blocks. Replayed trains during a
-parameter change do appear on TTLOUT2/3.
+parameter change do appear on TTLOUT2/3. The replayed train starts only ~0.3-0.6 s after
+the write (seen 2026-10-29), so configure_line waits until both PULSE outputs stayed low
+for PARAM_QUIET_TIME.
 
 Only the control port (8888) is used: the fields are written by setup_layout() at connect,
 the PCAP data capture is not touched. Timing resolution 8 ns (125 MHz FPGA clock).
@@ -129,6 +131,8 @@ class PandaLineTrigger(Device):
     TRIGGER_COUNTER = "COUNTER6"
     LINE_COUNTER = "COUNTER7"
     PULSE_COUNTER = "COUNTER8"
+    # a replayed train starts up to ~0.6 s after a parameter write
+    PARAM_QUIET_TIME = 1.0
     SHUTTER_OUTPUT = "TTLOUT2"
     DETECTOR_OUTPUT = "TTLOUT3"
 
@@ -282,25 +286,22 @@ class PandaLineTrigger(Device):
         self._pulse_params = params
 
     def _wait_pulses_idle(self, timeout: float) -> None:
-        """Wait until a replayed train is over: stable counter and both PULSE outputs low."""
+        """Wait until a replayed train is over: both PULSE outputs low for PARAM_QUIET_TIME."""
         sp, dp = self.SHUTTER_PULSE, self.DETECTOR_PULSE
-        deadline = time.time() + timeout
-        last = None
+        deadline = time.time() + timeout + self.PARAM_QUIET_TIME
+        last_active = time.time()
         while True:
-            time.sleep(0.02)
-            state = (
-                self.panda.get(f"{self.PULSE_COUNTER}.OUT"),
-                self.panda.get(f"{sp}.OUT"),
-                self.panda.get(f"{dp}.OUT"),
-            )
-            if state == last and state[1:] == ("0", "0"):
+            time.sleep(0.005)
+            now = time.time()
+            if self.panda.get(f"{sp}.OUT") != "0" or self.panda.get(f"{dp}.OUT") != "0":
+                last_active = now
+            elif now - last_active >= self.PARAM_QUIET_TIME:
                 return
-            if time.time() > deadline:
+            if now > deadline:
                 raise PandaLineTriggerError(
                     f"{self.name}: PULSE blocks still active {timeout:.1f} s after a parameter"
                     " change."
                 )
-            last = state
 
     def arm(self, one_shot: bool = False) -> None:
         """

tests/tests_devices/test_panda_line_trigger.py

@@ -52,6 +52,7 @@ class FakePanda(PandaControl):
 @pytest.fixture
 def trigger():
     device = PandaLineTrigger(name="pandatrig", host="fake-panda")
+    device.PARAM_QUIET_TIME = 0.01
     device.panda = FakePanda()
     device.wait_for_connection()
     return device
@@ -219,3 +220,24 @@ def test_falling_edge_inverts_the_input():
 def test_invalid_trigger_edge():
     with pytest.raises(ValueError, match="trigger_edge"):
         PandaLineTrigger(name="pandatrig", host="fake-panda", trigger_edge="both")
+
+
+def test_configure_line_waits_for_a_late_replayed_train(trigger):
+    """The replayed train starts only after the write; configure_line must outlast it."""
+    import threading
+    import time
+
+    trigger.PARAM_QUIET_TIME = 0.2
+    fields = trigger.panda.fields
+
+    def replay():
+        time.sleep(0.05)
+        fields["PULSE4.OUT"] = "1"
+        time.sleep(0.05)
+        fields["PULSE4.OUT"] = "0"
+
+    threading.Thread(target=replay, daemon=True).start()
+    t0 = time.time()
+    trigger.configure_line(5, 0.01)
+    # the train ended at ~0.1 s, then 0.2 s quiet
+    assert time.time() - t0 >= 0.28