Fix handling values in digital line scaler data

Only use the first bit to represent whether data is one or zero
adamreeve · Mar 29, 2020 · f1974e7 · f1974e7
1 parent 167884f
commit f1974e7
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Showing 2 changed files with 34 additions and 4 deletions.
diff --git a/nptdms/daqmx.py b/nptdms/daqmx.py
@@ -80,6 +80,8 @@ def _read_data_chunk(self, file, data_objects, chunk_index):
                     # should be correct
                     this_scaler_data.dtype = (
                         scaler.data_type.nptype.newbyteorder(self.endianness))
+                    if obj.daqmx_metadata.scaler_type == DIGITAL_LINE_SCALER:
+                        this_scaler_data = np.bitwise_and(this_scaler_data, 1)
                     scaler_data[obj.path][scaler.scale_id] = this_scaler_data
 
         return RawDataChunk.scaler_data(scaler_data)
@@ -143,17 +145,19 @@ class DaqMxMetadata(object):
 
     __slots__ = [
         'data_type',
+        'scaler_type',
         'dimension',
         'chunk_size',
         'raw_data_widths',
         'scalers',
         ]
 
-    def __init__(self, f, endianness, daqmx_segment_type):
+    def __init__(self, f, endianness, scaler_type):
         """
         Read the metadata for a DAQmx raw segment.  This is the raw
         DAQmx-specific portion of the raw data index.
         """
+        self.scaler_type = scaler_type
         self.data_type = types.tds_data_types[0xFFFFFFFF]
         self.dimension = types.Uint32.read(f, endianness)
         # In TDMS format version 2.0, 1 is the only valid value for dimension
@@ -165,7 +169,7 @@ def __init__(self, f, endianness, daqmx_segment_type):
         scaler_vector_length = types.Uint32.read(f, endianness)
         log.debug("mxDAQ format scaler vector size '%d'", scaler_vector_length)
         self.scalers = [
-            DaqMxScaler(f, endianness, daqmx_segment_type)
+            DaqMxScaler(f, endianness, scaler_type)
             for _ in range(scaler_vector_length)]
 
         # Read raw data widths.
@@ -201,14 +205,14 @@ class DaqMxScaler(object):
         'sample_format_bitmap',
         ]
 
-    def __init__(self, open_file, endianness, daqmx_segment_type):
+    def __init__(self, open_file, endianness, scaler_type):
         data_type_code = types.Uint32.read(open_file, endianness)
         self.data_type = DAQMX_TYPES[data_type_code]
 
         # more info for format changing scaler
         self.raw_buffer_index = types.Uint32.read(open_file, endianness)
         self.raw_byte_offset = types.Uint32.read(open_file, endianness)
-        if daqmx_segment_type == DIGITAL_LINE_SCALER:
+        if scaler_type == DIGITAL_LINE_SCALER:
             self.sample_format_bitmap = types.Uint8.read(open_file, endianness)
         else:
             self.sample_format_bitmap = types.Uint32.read(open_file, endianness)

diff --git a/nptdms/test/test_daqmx.py b/nptdms/test/test_daqmx.py
@@ -427,6 +427,32 @@ def test_digital_line_scaler_data():
     np.testing.assert_array_equal(data, [0, 1, 0, 1])
 
 
+def test_digital_line_scaler_data_uses_first_bit_of_bytes():
+    """ Test DAQmx digital line scaler data only uses the first bit in each byte to represent a 1 or 0 value
+    """
+
+    scaler_metadata = daqmx_scaler_metadata(0, 0, 2, digital_line_scaler=True)
+    metadata = segment_objects_metadata(
+        root_metadata(),
+        group_metadata(),
+        daqmx_channel_metadata("Channel1", 4, [4], [scaler_metadata], digital_line_scaler=True))
+    data = (
+        "00 00 00 00"
+        "00 00 01 00"
+        "00 00 02 00"
+        "00 00 03 00"
+    )
+
+    test_file = GeneratedFile()
+    test_file.add_segment(segment_toc(), metadata, data)
+    tdms_data = test_file.load()
+
+    data = tdms_data["Group"]["Channel1"].raw_data
+
+    assert data.dtype == np.uint8
+    np.testing.assert_array_equal(data, [0, 1, 0, 1])
+
+
 def test_lazily_reading_channel():
     """ Test loading channels individually from a DAQmx file
     """