c4m/nmigen/jtag/bus.py

   1 from nmigen import *
   2 from nmigen.hdl.rec import Direction
   3
   4 class Interface(Record):
   5     """JTAG Interface.
   6
   7     Parameters
   8     ----------
   9     with_reset : bool, default=False
  10         wether to include trst field; if this field is not present a JTAG master
  11         should not rely on this pin for resetting a TAP.
  12     """
  13     def __init__(self, *, with_reset=False, name=None, src_loc_at=0):
  14         layout = [
  15             ("tck", 1, Direction.NONE),
  16             ("tms", 1, Direction.NONE),
  17             ("tdo", 1, Direction.FANOUT),
  18             ("tdi", 1, Direction.FANIN),
  19         ]
  20         if with_reset:
  21             layout.append(
  22                 ("trst", 1, Direction.FANOUT)
  23             )
  24         super().__init__(layout, name=name, src_loc_at=src_loc_at+1)
  25
  26
  27 class Chain(Elaboratable):
  28     """A chain of JTAG interfaces.
  29
  30     Parameters
  31     ----------
  32     buses : iterable of :class:`Interface`, default=[]
  33         Initial value of the buses in the chain.
  34     with_reset : bool, default=False
  35         Wether the generated bus has a reset pin. If value is True all buses in
  36         the chain also have to have a reset signal
  37
  38     Attributes
  39     ----------
  40     bus : :class:`Interface`
  41     """
  42     def __init__(self, *, with_reset=False, buses=[], name=None, src_loc_at=0):
  43         for bus in buses:
  44             if not isinstance(bus, Interface):
  45                 raise ValueError("Object in buses that is not a JTAG Interface")
  46             if with_reset and not hasattr(bus, "trst"):
  47                 raise ValueError("JTAG bus in buses without a reset signal")
  48
  49         kwargs = {
  50             "with_reset": with_reset,
  51             "src_loc_at": src_loc_at + 1,
  52         }
  53         if name is not None:
  54             kwargs["name"] = name + "_bus"
  55         self.bus = Interface(**kwargs)
  56
  57         self._buses = buses
  58
  59     def add(bus):
  60         """Add a bus to the chain"""
  61
  62         if not isinstance(bus, Interface):
  63             raise ValueError("bus in not a JTAG Interface")
  64         if hasattr(self.bus, "trst") and not hasattr(bus, "trst"):
  65             raise ValueError("bus needs to have a reset signal")
  66         self._buses.append(bus)
  67
  68     def elaborate(self, platform):
  69         with_reset = hasattr(self.bus, "trst")
  70
  71         m = Module()
  72
  73         # Connect first and last
  74         m.d.comb += [
  75             self._buses[0].tdi.eq(self.bus.tdo),
  76             self.bus.tdi.eq(self._buses[-1].tdo),
  77         ]
  78         for i in range(len(self._buses)):
  79             if i < len(self._buses) - 1:
  80                 m.d.comb += self._buses[i+1].tdi.eq(self._buses[i].tdo)
  81             if with_reset:
  82                 m.d.comb += self._buses[i].trst.eq(self.bus.trst)
  83
  84         return m