How to use the pisa.PisaInst function in pisa

try:

        # Update instruction counts

        s.num_total_inst += 1
        if s.isa.stats_en:
          s.num_inst += 1

        # Set trace string in case the fetch yields

        s.trace = " "*29

        # Fetch instruction

        s.pc   = s.isa.PC.uint()
        s.inst = PisaInst( s.imem[ s.pc : s.pc+4 ] )

        # Set trace string in case the execution function yeilds

        s.trace = "#".ljust(29)

        # Execute instruction

        s.isa.execute( s.inst )

        # Ensure that the stats_en and status ports are current

        if not s.test_en:
          s.stats_en.next = s.isa.stats_en
          s.status.next   = s.isa.status

        # Trace instruction

if s.ifetch_wait > 0:

        s.trace_X = "~w{}".format(s.ifetch_wait).ljust(29)
        if not s.imemresp_q.empty():
          inst = PisaInst(s.imemresp_q.first())
          s.ifetch_wait -= 1
          s.trace_X = "~w{}".format(s.ifetch_wait).ljust(29)
          s.imemresp_q.deq()

      elif     not s.pc_queue_FX.empty() \
           and not s.imemresp_q.empty() \
           and not s.inst_queue_XW.full() \
           and not s.wb_queue_XW.full():

        s.stall_X = False
        inst = PisaInst(s.imemresp_q.first())
        s.execute_dispatch[inst.name]( s, inst )

        if not s.stall_X:
          if not s.pc_queue_FX.empty():
            s.pc_queue_FX.deq()
            s.imemresp_q.deq()
          s.inst_queue_XW.enq( inst )
          s.trace_X = str(inst).ljust(29)
        else:
          s.trace_X = ( "#" + s.stall_type_X ).ljust(29)

      # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      # F: Fetch Pipeline Stage
      # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

      s.trace_F = "  ".ljust(8)

if not s.stall_W:
          s.inst_queue_XW.deq()
          s.wb_queue_XW.deq()

      # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      # X: Execute Pipeline Stage
      # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

      s.trace_X = " "*29

      if s.ifetch_wait > 0:

        s.trace_X = "~w{}".format(s.ifetch_wait).ljust(29)
        if not s.imemresp_q.empty():
          inst = PisaInst(s.imemresp_q.first())
          s.ifetch_wait -= 1
          s.trace_X = "~w{}".format(s.ifetch_wait).ljust(29)
          s.imemresp_q.deq()

      elif     not s.pc_queue_FX.empty() \
           and not s.imemresp_q.empty() \
           and not s.inst_queue_XW.full() \
           and not s.wb_queue_XW.full():

        s.stall_X = False
        inst = PisaInst(s.imemresp_q.first())
        s.execute_dispatch[inst.name]( s, inst )

        if not s.stall_X:
          if not s.pc_queue_FX.empty():
            s.pc_queue_FX.deq()