code: def scratch_xtensa_matmul(mace_op, mace_net):
      output_channels = mace_op.output_shape[0].dims[1]
      bias_bytes = output_channels * 4
      return bias_bytes
  
file_path: mace/tools/python/micro/micro_op_resolver_xtensa_rules.py
imports: from enum import Enum
  from micro.micro_op_resolver_rules import MicroOPSResolverRule
  from py_proto import mace_pb2
  from transform.base_converter import MaceKeyword
  from transform.base_converter import MaceOp
  from utils.config_parser import DataFormat
  from utils.config_parser import ModelKeys
  from utils.config_parser import Platform
  from utils.util import mace_check
  from utils.net_util import NetUtil
label_desc: Use image node_id 2 for calling a global function with example usage: scratch_xtensa_matmul(mace_op, mace_net) and returns: bias_bytes