diff --git a/README.md b/README.md
index fe18cc2..14cf50f 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@ Formally verified implementation of the ARTIQ RTIO core in nMigen
 - Devise a suitable migration strategy for `artiq.gateware.rtio` from Migen to nMigen
 - [ ] Implement the core in nMigen
 - - [x] `rtio.cri` (`Interface` and `CRIDecoder` only)
-- - [ ] `rtio.rtlink`
+- - [x] `rtio.rtlink`
 - - [ ] `rtio.sed.layouts`
 - - [ ] `rtio.sed.output_network`
 - - [ ] `rtio.sed.output_driver`
diff --git a/rtio/rtlink.py b/rtio/rtlink.py
new file mode 100644
index 0000000..cd9d0e0
--- /dev/null
+++ b/rtio/rtlink.py
@@ -0,0 +1,90 @@
+from nmigen import *
+
+class OInterface(object):
+    def __init__(self, data_width, address_width=0,
+        fine_ts_width=0, enable_replace=True,
+        delay=0):
+        self.stb = Signal()
+        self.busy = Signal()
+
+        assert 0 <= data_width <= 512
+        assert 0 <= address_width <= 8
+        assert 0 <= fine_ts_width <= 4
+
+        if data_width:
+            self.data = Signal(data_width, reset_less=True)
+        if address_width:
+            self.address = Signal(address_width, reset_less=True)
+        if fine_ts_width:
+            self.fine_ts = Signal(fine_ts_width, reset_less=True)
+
+        self.enable_replace = enable_replace
+
+        if delay < 0:
+            raise ValueError("only positive delays allowed", delay)
+        self.delay = delay
+
+    @classmethod
+    def like(cls, other):
+        return cls(get_data_width(other),
+            get_address_width(other),
+            get_fine_ts_width(other),
+            other.enable_replace,
+            other.delay)
+
+class IInterface(object):
+    def __init__(self, data_width,
+        timestamped=True, fine_ts_width=0, delay=0):
+        self.stb = Signal()
+
+        assert 0 <= data_width <= 32
+        assert 0 <= fine_ts_width <= 4
+
+        if data_width:
+            self.data = Signal(data_width, reset_less=True)
+        if fine_ts_width:
+            self.fine_ts = Signal(fine_ts_width, reset_less=True)
+
+        assert(not fine_ts_width or timestamped)
+        self.timestamped = timestamped
+        if delay < 0:
+            raise ValueError("only positive delays")
+        self.delay = delay
+
+    @classmethod
+    def like(cls, other):
+        return cls(get_data_width(other),
+            other.timestamped,
+            get_fine_ts_width(other),
+            other.delay)
+
+class Interface(object):
+    def __init__(self, o, i=None):
+        self.o = o
+        self.i = i
+
+    @classmethod
+    def like(cls, other):
+        if other.i is None:
+            return cls(OInterface.like(other.o))
+        else:
+            return cls(OInterface.like(other.o),
+                IInterface.like(other.i))
+
+def _get_or_zero(interface, attr):
+    if interface is None:
+        return 0
+    assert isinstance(interface, (OInterface, IInterface))
+    if hasattr(interface, attr):
+        return len(getattr(interface, attr))
+    else:
+        return 0
+
+def get_data_width(interface):
+    return _get_or_zero(interface, "data")
+
+def get_address_width(interface):
+    return _get_or_zero(interface, "address")
+
+def get_fine_ts_width(interface):
+    return _get_or_zero(interface, "fine_ts")