From 85d7ce239ef57731cc1dcb2c8ffc6ffc85f77a5d Mon Sep 17 00:00:00 2001
From: Staf Verhaegen <staf@stafverhaegen.be>
Date: Thu, 5 Dec 2019 20:43:26 +0100
Subject: [PATCH] Added JTAG bus interface.

---
 c4m/nmigen/jtag/__init__.py |  1 +
 c4m/nmigen/jtag/bus.py      | 84 +++++++++++++++++++++++++++++++++++++
 2 files changed, 85 insertions(+)
 create mode 100644 c4m/nmigen/jtag/bus.py

diff --git a/c4m/nmigen/jtag/__init__.py b/c4m/nmigen/jtag/__init__.py
index bfa7957..9e6cc09 100644
--- a/c4m/nmigen/jtag/__init__.py
+++ b/c4m/nmigen/jtag/__init__.py
@@ -1 +1,2 @@
 from .pmod import *
+from .bus import *
diff --git a/c4m/nmigen/jtag/bus.py b/c4m/nmigen/jtag/bus.py
new file mode 100644
index 0000000..c6015a7
--- /dev/null
+++ b/c4m/nmigen/jtag/bus.py
@@ -0,0 +1,84 @@
+from nmigen import *
+from nmigen.hdl.rec import Direction
+
+class Interface(Record):
+    """JTAG Interface.
+
+    Parameters
+    ----------
+    with_reset : bool, default=False
+        wether to include trst field; if this field is not present a JTAG master
+        should not rely on this pin for resetting a TAP.
+    """
+    def __init__(self, *, with_reset=False, name=None, src_loc_at=0):
+        layout = [
+            ("tck", 1, Direction.NONE),
+            ("tms", 1, Direction.NONE),
+            ("tdo", 1, Direction.FANOUT),
+            ("tdi", 1, Direction.FANIN),
+        ]
+        if with_reset:
+            layout.append(
+                ("trst", 1, Direction.FANOUT)
+            )
+        super().__init__(layout, name=name, src_loc_at=src_loc_at+1)
+
+
+class Chain(Elaboratable):
+    """A chain of JTAG interfaces.
+
+    Parameters
+    ----------
+    buses : iterable of :class:`Interface`, default=[]
+        Initial value of the buses in the chain.
+    with_reset : bool, default=False
+        Wether the generated bus has a reset pin. If value is True all buses in
+        the chain also have to have a reset signal
+
+    Attributes
+    ----------
+    bus : :class:`Interface`
+    """
+    def __init__(self, *, with_reset=False, buses=[], name=None, src_loc_at=0):
+        for bus in buses:
+            if not isinstance(bus, Interface):
+                raise ValueError("Object in buses that is not a JTAG Interface")
+            if with_reset and not hasattr(bus, "trst"):
+                raise ValueError("JTAG bus in buses without a reset signal")
+
+        kwargs = {
+            "with_reset": with_reset,
+            "src_loc_at": src_loc_at + 1,
+        }
+        if name is not None:
+            kwargs["name"] = name + "_bus"
+        self.bus = Interface(**kwargs)
+
+        self._buses = buses
+
+    def add(bus):
+        """Add a bus to the chain"""
+
+        if not isinstance(bus, Interface):
+            raise ValueError("bus in not a JTAG Interface")
+        if hasattr(self.bus, "trst") and not hasattr(bus, "trst"):
+            raise ValueError("bus needs to have a reset signal")
+        self._buses.append(bus)
+
+    def elaborate(self, platform):
+        with_reset = hasattr(self.bus, "trst")
+
+        m = Module()
+
+        # Connect first and last
+        m.d.comb += [
+            self._buses[0].tdi.eq(self.bus.tdo),
+            self.bus.tdi.eq(self._buses[-1].tdo),
+        ]
+        for i in range(len(self._buses)):
+            if i < len(self._buses) - 1:
+                m.d.comb += self._buses[i+1].tdi.eq(self._buses[i].tdo)
+            if with_reset:
+                m.d.comb += self._buses[i].trst.eq(self.bus.trst)
+
+        return m
-- 
2.30.2