def build_p37_fcos_dla_bifpn_backbone(cfg, input_shape: ShapeSpec):
    """
    Args:
        cfg: a detectron2 CfgNode
    Returns:
        backbone (Backbone): backbone module, must be a subclass of :class:`Backbone`.
    """
    bottom_up = dla34(cfg)
    in_features = cfg.MODEL.FPN.IN_FEATURES
    out_channels = cfg.MODEL.BIFPN.OUT_CHANNELS
    num_repeats = cfg.MODEL.BIFPN.NUM_BIFPN
    assert cfg.MODEL.BIFPN.NUM_LEVELS == 5
    top_levels = 2

    backbone = BiFPN(
        bottom_up=bottom_up,
        in_features=in_features,
        out_channels=out_channels,
        num_top_levels=top_levels,
        num_repeats=num_repeats,
        norm=cfg.MODEL.BIFPN.NORM
    )
    return backbone

    Args:
        cfg: a detectron2 CfgNode
    Returns:
        backbone (Backbone): backbone module, must be a subclass of :class:`Backbone`.
    
video_chat_with_MOSS/models/grit_src/third_party/CenterNet2/projects/CenterNet2/centernet/modeling/backbone/bifpn_fcos.py