code: def _read_assoc_file(fid):
      """Read BTi PDF assocfile."""
      out = {"file_id": read_int16(fid), "length": read_int16(fid)}
  
      fid.seek(32, 1)
      out["checksum"] = read_int32(fid)
  
      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 14 for calling a global function with example usage: _read_assoc_file(fid) and returns: out