c4m/nmigen/jtag/bus.py

   1 from nmigen import *
   2 from nmigen.hdl.rec import Direction
   3
   4
   5 class DMIInterface(Record):
   6     def __init__(self, name=None, addr_wid=4, data_wid=64):
   7         layout = [
   8            ('addr_i', addr_wid, Direction.FANIN),  # DMI register address
   9            ('din',    data_wid, Direction.FANIN),  # DMI data write in (we=1)
  10            ('dout',   data_wid, Direction.FANOUT), # DMI data read out (we=0)
  11            ('req_i',  1,        Direction.FANIN),  # DMI request valid (stb)
  12            ('we_i',   1,        Direction.FANIN),  # DMI write-enable
  13            ('ack_o',  1,        Direction.FANOUT), # DMI ack request
  14         ]
  15         super().__init__(name=name, layout=layout)
  16
  17
  18 class Interface(Record):
  19     """JTAG Interface.
  20
  21     Parameters
  22     ----------
  23     with_reset : bool, default=False
  24         wether to include trst field; if this field is not present a JTAG master
  25         should not rely on this pin for resetting a TAP.
  26     """
  27     def __init__(self, *, with_reset=False, name=None, src_loc_at=0):
  28         layout = [
  29             ("tck", 1, Direction.NONE),
  30             ("tms", 1, Direction.NONE),
  31             ("tdo", 1, Direction.FANOUT),
  32             ("tdi", 1, Direction.FANIN),
  33         ]
  34         if with_reset:
  35             layout.append(
  36                 ("trst", 1, Direction.FANOUT)
  37             )
  38         super().__init__(layout, name=name, src_loc_at=src_loc_at+1)
  39
  40
  41 class Chain(Elaboratable):
  42     """A chain of JTAG interfaces.
  43
  44     Parameters
  45     ----------
  46     buses : iterable of :class:`Interface`, default=[]
  47         Initial value of the buses in the chain.
  48     with_reset : bool, default=False
  49         Wether the generated bus has a reset pin. If value is True all buses in
  50         the chain also have to have a reset signal
  51
  52     Attributes
  53     ----------
  54     bus : :class:`Interface`
  55     """
  56     def __init__(self, *, with_reset=False, buses=[], name=None, src_loc_at=0):
  57         for bus in buses:
  58             if not isinstance(bus, Interface):
  59                 raise ValueError("Object in buses that is not a JTAG Interface")
  60             if with_reset and not hasattr(bus, "trst"):
  61                 raise ValueError("JTAG bus in buses without a reset signal")
  62
  63         kwargs = {
  64             "with_reset": with_reset,
  65             "src_loc_at": src_loc_at + 1,
  66         }
  67         if name is not None:
  68             kwargs["name"] = name + "_bus"
  69         self.bus = Interface(**kwargs)
  70
  71         self._buses = buses
  72
  73     def add(bus):
  74         """Add a bus to the chain"""
  75
  76         if not isinstance(bus, Interface):
  77             raise ValueError("bus in not a JTAG Interface")
  78         if hasattr(self.bus, "trst") and not hasattr(bus, "trst"):
  79             raise ValueError("bus needs to have a reset signal")
  80         self._buses.append(bus)
  81
  82     def elaborate(self, platform):
  83         with_reset = hasattr(self.bus, "trst")
  84
  85         m = Module()
  86
  87         # Connect first and last
  88         m.d.comb += [
  89             self._buses[0].tdi.eq(self.bus.tdo),
  90             self.bus.tdi.eq(self._buses[-1].tdo),
  91         ]
  92         for i in range(len(self._buses)):
  93             if i < len(self._buses) - 1:
  94                 m.d.comb += self._buses[i+1].tdi.eq(self._buses[i].tdo)
  95             if with_reset:
  96                 m.d.comb += self._buses[i].trst.eq(self.bus.trst)
  97
  98         return m