diff --git a/artiq/gateware/drtio/cdc.py b/artiq/gateware/drtio/cdc.py
new file mode 100644
index 000000000..9edd8a1b4
--- /dev/null
+++ b/artiq/gateware/drtio/cdc.py
@@ -0,0 +1,55 @@
+from migen import *
+
+from migen.genlib.cdc import PulseSynchronizer
+
+
+class CrossDomainRequest(Module):
+    def __init__(self, domain,
+                 req_stb, req_ack, req_data,
+                 srv_stb, srv_ack, srv_data):
+        dsync = getattr(self.sync, domain)
+
+        request = PulseSynchronizer("sys", domain)
+        reply = PulseSynchronizer(domain, "sys")
+        self.submodules += request, reply
+
+        ongoing = Signal()
+        self.comb += request.i.eq(~ongoing & req_stb)
+        self.sync += [
+            req_ack.eq(reply.o),
+            If(req_stb, ongoing.eq(1)),
+            If(req_ack, ongoing.eq(0))
+        ]
+        if req_data is not None:
+            req_data_r = Signal.like(req_data)
+            req_data_r.attr.add("no_retiming")
+            self.sync += If(req_stb, req_data_r.eq(req_data))
+        dsync += [
+            If(request.o, srv_stb.eq(1)),
+            If(srv_ack, srv_stb.eq(0))
+        ]
+        if req_data is not None:
+            dsync += If(request.o, srv_data.eq(req_data_r))
+        self.comb += reply.i.eq(srv_stb & srv_ack)
+
+
+class CrossDomainNotification(Module):
+    def __init__(self, domain, rdomain,
+                 emi_stb, emi_data,
+                 rec_stb, rec_ack, rec_data):
+        emi_data_r = Signal(len(emi_data))
+        emi_data_r.attr.add("no_retiming")
+        dsync = getattr(self.sync, domain)
+        dsync += If(emi_stb, emi_data_r.eq(emi_data))
+
+        ps = PulseSynchronizer(domain, rdomain)
+        self.submodules += ps
+        self.comb += ps.i.eq(emi_stb)
+        rsync = getattr(self.sync, rdomain)
+        rsync += [
+            If(rec_ack, rec_stb.eq(0)),
+            If(ps.o,
+                rec_data.eq(emi_data_r),
+                rec_stb.eq(1)
+            )
+        ]
diff --git a/artiq/gateware/rtio/tsc.py b/artiq/gateware/rtio/tsc.py
new file mode 100644
index 000000000..e93744553
--- /dev/null
+++ b/artiq/gateware/rtio/tsc.py
@@ -0,0 +1,48 @@
+from migen import *
+
+from artiq.gateware.rtio.cdc import GrayCodeTransfer
+
+
+class TSC(Module):
+    def __init__(self, mode, glbl_fine_ts_width=0):
+        self.glbl_fine_ts_width = glbl_fine_ts_width
+
+        # in rtio domain
+        self.coarse_ts = Signal(64 - glbl_fine_ts_width)
+        self.full_ts = Signal(64)
+        
+        # in sys domain
+        # monotonic, may lag behind the counter in the IO clock domain, but
+        # not be ahead of it.
+        self.coarse_ts_sys = Signal.like(self.coarse_ts)
+        self.full_ts_sys = Signal(64)
+
+        # in rtio domain
+        self.load = Signal()
+        self.load_value = Signal.like(self.coarse_ts)
+
+        if mode == "async":
+            self.full_ts_cri = self.full_ts_sys
+        elif mode == "sync":
+            self.full_ts_cri = self.full_ts
+        else:
+            raise ValueError
+
+        # # #
+
+        self.sync.rtio += If(self.load,
+                self.coarse_ts.eq(self.load_value)
+            ).Else(
+                self.coarse_ts.eq(self.coarse_ts + 1)
+            )
+        coarse_ts_cdc = GrayCodeTransfer(len(self.coarse_ts))  # from rtio to sys
+        self.submodules += coarse_ts_cdc
+        self.comb += [
+            coarse_ts_cdc.i.eq(self.coarse_ts),
+            self.coarse_ts_sys.eq(coarse_ts_cdc.o)
+        ]
+
+        self.comb += [
+            self.full_ts.eq(self.coarse_ts << glbl_fine_ts_width),
+            self.full_ts_sys.eq(self.coarse_ts_sys << glbl_fine_ts_width)
+        ]