Improve the device kit exposure timing.

nion/device_kit/CameraDevice.py

@@ -304,17 +304,20 @@ def __direct_acquire(self, cancel_event: threading.Event, do_sync: bool = False)
         # if do_sync is True, the scan device will sync with its acquisition thread before
         # advancing the pixel. this avoids race conditions of when the pixel count gets reset.
         # this will be set only for the first frame in a sequence.
-        start = time.time()
+        start = time.perf_counter()
         readout_area = self.readout_area
         binning_shape = Geometry.IntSize(self.__binning, self.__binning if self.__symmetric_binning else 1)
         # scan device is only set during synchronized acquisition
         if self.__scan_device:
             self.__scan_device.advance_pixel(do_sync=do_sync)
         xdata = self.__simulator.get_frame_data(Geometry.IntRect.from_tlbr(*readout_area), binning_shape, self.__exposure, self.__instrument.scan_context, self.__instrument.probe_position)
         self.__acquired_one_event.set()
-        elapsed = time.time() - start
+        elapsed = time.perf_counter() - start
         wait_s = max(self.__exposure - elapsed, 0)
         if not cancel_event.wait(wait_s):
+            actual_elapsed_s = time.perf_counter() - start
+            if actual_elapsed_s < self.__exposure:
+                time.sleep(self.__exposure - actual_elapsed_s)  # adjust in case the wait returns early (observed on python 3.13/windows)
             # thread event was not triggered during wait; signal that we have data
             xdata._set_timestamp(DateTime.utcnow())
             self.__xdata_buffer = xdata

nion/device_kit/ScanDevice.py

@@ -42,7 +42,7 @@ def __init__(self, frame_number: int, channels: typing.List[Channel], frame_para
         self.complete = False
         self.bad = False
         self.data_count = 0
-        self.start_time = time.time()
+        self.start_time = time.perf_counter()
         self.scan_data: typing.Optional[typing.List[_NDArray]] = None
 
 
@@ -298,7 +298,7 @@ def read_partial(self, frame_number: typing.Optional[int], pixels_to_skip: int)
                 pixels_remaining = min(total_pixels - current_frame.data_count, int(time_slice * 1e6 / frame_parameters.pixel_time_us) + 1)
                 pixel_wait = min(pixels_remaining * frame_parameters.pixel_time_us / 1E6, time_slice)
                 time.sleep(pixel_wait)
-                target_count = min(int((time.time() - current_frame.start_time) / (frame_parameters.pixel_time_us / 1E6)), total_pixels)
+                target_count = min(int((time.perf_counter() - current_frame.start_time) / (frame_parameters.pixel_time_us / 1E6)), total_pixels)
             if (new_pixels := target_count - self.__scan_simulator.current_pixel_flat) > 0:
                 self.__scan_simulator._advance_pixel(new_pixels)
 

nion/instrumentation/test/CameraControl_test.py

@@ -509,7 +509,6 @@ def test_first_view_uses_correct_exposure(self):
             hardware_source.start_playing(sync_timeout=3.0)
             try:
                 hardware_source.get_next_xdatas_to_finish()  # view again
-                time.sleep(0.001)  # try to avoid Windows timer low precision issues
                 elapsed = time.perf_counter() - start
                 document_controller.periodic()
                 self.assertEqual(document_model.data_items[0].data_shape, hardware_source.get_expected_dimensions(4))