diff --git a/src/gateware/zc706.py b/src/gateware/zc706.py
index 086b038..95441fe 100755
--- a/src/gateware/zc706.py
+++ b/src/gateware/zc706.py
@@ -416,6 +416,22 @@ class _SatelliteBase(SoCCore):
         self.csr_devices.append("routing_table")
 
 
+class _Simple_RTIO:
+    def __init__(self):
+        platform = self.platform
+
+        rtio_channels = []
+        for i in range(4):
+            phy = ttl_simple.Output(platform.request("user_led", i))
+            self.submodules += phy
+            rtio_channels.append(rtio.Channel.from_phy(phy))
+
+        self.config["RTIO_LOG_CHANNEL"] = len(rtio_channels)
+        rtio_channels.append(rtio.LogChannel())
+
+        self.add_rtio(rtio_channels)
+
+
 class _NIST_CLOCK_RTIO:
     """
     NIST clock hardware, with old backplane and 11 DDS channels
@@ -514,6 +530,22 @@ class _NIST_QC2_RTIO:
 
         self.add_rtio(rtio_channels)
 
+
+class Simple(ZC706, _Simple_RTIO):
+    def __init__(self, acpki):
+        ZC706.__init__(self, acpki)
+        _Simple_RTIO.__init__(self)
+
+class Master(_MasterBase, _Simple_RTIO):
+    def __init__(self, acpki):
+        _MasterBase.__init__(self, acpki)
+        _Simple_RTIO.__init__(self)
+
+class Satellite(_SatelliteBase, _Simple_RTIO):
+    def __init__(self, acpki):
+        _SatelliteBase.__init__(self, acpki)
+        _Simple_RTIO.__init__(self)
+
 class NIST_CLOCK(ZC706, _NIST_CLOCK_RTIO):
     def __init__(self, acpki):
         ZC706.__init__(self, acpki)
@@ -546,7 +578,8 @@ class NIST_QC2_Satellite(_SatelliteBase, _NIST_QC2_RTIO):
         _NIST_QC2_RTIO.__init__(self)
 
 
-VARIANTS = {cls.__name__.lower(): cls for cls in [NIST_CLOCK, NIST_CLOCK_Master, NIST_CLOCK_Satellite,
+VARIANTS = {cls.__name__.lower(): cls for cls in [Simple, Master, Satellite, 
+                                                  NIST_CLOCK, NIST_CLOCK_Master, NIST_CLOCK_Satellite,
                                                   NIST_QC2, NIST_QC2_Master, NIST_QC2_Satellite]}
 
 
@@ -581,9 +614,9 @@ def main():
         help="build Rust compiler configuration into the specified file")
     parser.add_argument("-g", default=None,
         help="build gateware into the specified directory")
-    parser.add_argument("-V", "--variant", default="nist_clock",
+    parser.add_argument("-V", "--variant", default="simple",
                         help="variant: "
-                             "[acpki_]nist_clock/nist_qc2[_master/_satellite] "
+                             "[acpki_]simple/nist_clock/nist_qc2 "
                              "(default: %(default)s)")
     args = parser.parse_args()