Changed to trigger on lower position, rather than midpoint

Author: tomtrafford

src/ophyd_async/fastcs/panda/_trigger.py

@@ -88,7 +88,7 @@ async def prepare(self, value: ScanSpecInfo):
             rows += SeqTable.row(
                 trigger=trig,
                 position=int(
-                    chunk.midpoints[fast_axis][start]
+                    chunk.lower[fast_axis][start]
                     / await fast_axis.encoder_res.get_value()
                 ),
             )

tests/fastcs/panda/test_trigger.py

@@ -115,7 +115,7 @@ async def test_seq_scanspec_trigger_logic(mock_panda, sim_x_motor, sim_y_motor)
         SeqTrigger.IMMEDIATE,
         SeqTrigger.BITA_0,
     ]
-    assert (out.position == [0, 0, 50, 0, 0, 0, 250, 0, 0, 0, 50, 0, 0]).all()
+    assert (out.position == [0, 0, 25, 0, 0, 0, 275, 0, 0, 0, 25, 0, 0]).all()
     assert (out.time1 == [0, 0, 0, 900000, 0, 0, 0, 900000, 0, 0, 0, 900000, 0]).all()
     assert (out.time2 == [0, 0, 0, 100000, 0, 0, 0, 100000, 0, 0, 0, 100000, 0]).all()