Fix reading bad cnt chans

mne/io/cnt/cnt.py

@@ -169,6 +169,8 @@ def read_raw_cnt(
     emg=(),
     data_format="auto",
     date_format="mm/dd/yy",
+    *,
+    header="old",
     preload=False,
     verbose=None,
 ):
@@ -219,6 +221,9 @@ def read_raw_cnt(
         Defaults to ``'auto'``.
     date_format : ``'mm/dd/yy'`` | ``'dd/mm/yy'``
         Format of date in the header. Defaults to ``'mm/dd/yy'``.
+    header : ``'new'`` | ``'old'``
+        Defines the header format. Used to describe how bad channels
+        are formatted.
     %(preload)s
     %(verbose)s
 
@@ -244,12 +249,13 @@ def read_raw_cnt(
         emg=emg,
         data_format=data_format,
         date_format=date_format,
+        header=header,
         preload=preload,
         verbose=verbose,
     )
 
 
-def _get_cnt_info(input_fname, eog, ecg, emg, misc, data_format, date_format):
+def _get_cnt_info(input_fname, eog, ecg, emg, misc, data_format, date_format, header):
     """Read the cnt header."""
     data_offset = 900  # Size of the 'SETUP' header.
     cnt_info = dict()
@@ -344,7 +350,12 @@ def _get_cnt_info(input_fname, eog, ecg, emg, misc, data_format, date_format):
             fid.seek(data_offset + 75 * ch_idx)
             ch_name = read_str(fid, 10)
             ch_names.append(ch_name)
-            fid.seek(data_offset + 75 * ch_idx + 4)
+
+            # Some files have bad channels marked differently in the header.
+            if header == "new":
+                fid.seek(data_offset + 75 * ch_idx + 14)
+            if header == "old":
+                fid.seek(data_offset + 75 * ch_idx + 4)
             if np.fromfile(fid, dtype="u1", count=1).item():
                 bads.append(ch_name)
             fid.seek(data_offset + 75 * ch_idx + 19)
@@ -451,6 +462,9 @@ class RawCNT(BaseRaw):
         Defaults to ``'auto'``.
     date_format : ``'mm/dd/yy'`` | ``'dd/mm/yy'``
         Format of date in the header. Defaults to ``'mm/dd/yy'``.
+    header : ``'new'`` | ``'old'``
+        Defines the header format. Used to describe how bad channels
+        are formatted.
     %(preload)s
     stim_channel : bool | None
         Add a stim channel from the events. Defaults to None to trigger a
@@ -478,6 +492,8 @@ def __init__(
         emg=(),
         data_format="auto",
         date_format="mm/dd/yy",
+        *,
+        header="old",
         preload=False,
         verbose=None,
     ):  # noqa: D102
@@ -489,7 +505,7 @@ def __init__(
 
         input_fname = path.abspath(input_fname)
         info, cnt_info = _get_cnt_info(
-            input_fname, eog, ecg, emg, misc, data_format, _date_format
+            input_fname, eog, ecg, emg, misc, data_format, _date_format, header
         )
         last_samps = [cnt_info["n_samples"] - 1]
         super(RawCNT, self).__init__(

mne/io/cnt/tests/test_cnt.py

@@ -19,7 +19,7 @@
 
 
 @testing.requires_testing_data
-def test_data():
+def test_old_data():
     """Test reading raw cnt files."""
     with pytest.warns(RuntimeWarning, match="number of bytes"):
         raw = _test_raw_reader(
@@ -37,6 +37,15 @@ def test_data():
     assert raw.info["meas_date"] is None
 
 
+@testing.requires_testing_data
+def test_new_data():
+    """Test reading raw cnt files with different header."""
+    with pytest.warns(RuntimeWarning):
+        raw = read_raw_cnt(input_fname=fname_bad_spans, header="new")
+
+    assert raw.info["bads"] == ["F8"]  # test bads
+
+
 @testing.requires_testing_data
 def test_compare_events_and_annotations():
     """Test comparing annotations and events."""