code: def _read_epoch(fid):
      """Read BTi PDF epoch."""
      out = {
          "pts_in_epoch": read_int32(fid),
          "epoch_duration": read_float(fid),
          "expected_iti": read_float(fid),
          "actual_iti": read_float(fid),
          "total_var_events": read_int32(fid),
          "checksum": read_int32(fid),
          "epoch_timestamp": read_int32(fid),
      }
  
      fid.seek(28, 1)
  
      return out
  
imports: import functools
  import os.path
  from io import BytesIO
  from itertools import count
  import numpy
  from ..._fiff._digitization import _make_bti_dig_points
  from ..._fiff.constants import FIFF
  from ..._fiff.meas_info import _empty_info
  from ..._fiff.tag import _coil_trans_to_loc, _loc_to_coil_trans
  from ..._fiff.utils import _mult_cal_one, read_str
  from ...transforms import Transform, combine_transforms, invert_transform
  from ...utils import _stamp_to_dt, _validate_type, logger, path_like, verbose
  from ..base import BaseRaw
  from .constants import BTI
  from .read import read_char, read_dev_header, read_double, read_double_matrix, read_float, read_float_matrix, read_int16, read_int16_matrix, read_int32, read_int64, read_transform, read_uint16, read_uint32
label_desc: Use image node_id 10 for calling a global function with example usage: _read_epoch(fid) and returns: out