diff --git a/README.md b/README.md
index 1db5433b..029ff0f1 100644
--- a/README.md
+++ b/README.md
@@ -45,7 +45,7 @@ Note: if you are using Nix channels the first time, you need to be aware of this
 Pure build with Nix and execution on a remote JTAG server:
 
 ```shell
-nix-build -A zc706-simple-jtag  # or zc706-nist_qc2-jtag or zc706-nist_clock-jtag
+nix-build -A zc706-nist_clock-jtag  # or zc706-nist_qc2-jtag or zc706-nist_clock_satellite-jtag
 ./remote_run.sh
 ```
 
diff --git a/default.nix b/default.nix
index 2826ce1c..dbac0c10 100644
--- a/default.nix
+++ b/default.nix
@@ -8,7 +8,7 @@ let
   vivado = import <artiq-fast/vivado.nix> { inherit pkgs; };
   # FSBL configuration supplied by Vivado 2020.1 for these boards:
   fsblTargets = ["zc702" "zc706" "zed"];
-  sat_variants = ["satellite" "acpki_satellite" "nist_clock_satellite" "nist_qc2_satellite"];
+  sat_variants = ["acpki_satellite" "nist_clock_satellite" "nist_qc2_satellite"];
   build = { target, variant, json ? null }: let
     szl = (import zynq-rs)."${target}-szl";
     fsbl = import "${zynq-rs}/nix/fsbl.nix" {
@@ -133,18 +133,12 @@ let
   );
 in
   (
-    (build { target = "zc706"; variant = "simple"; }) //
-    (build { target = "zc706"; variant = "master"; }) //
-    (build { target = "zc706"; variant = "satellite"; }) //
     (build { target = "zc706"; variant = "nist_clock"; }) //
     (build { target = "zc706"; variant = "nist_clock_master"; }) //
     (build { target = "zc706"; variant = "nist_clock_satellite"; }) //
     (build { target = "zc706"; variant = "nist_qc2"; }) //
     (build { target = "zc706"; variant = "nist_qc2_master"; }) //
     (build { target = "zc706"; variant = "nist_qc2_satellite"; }) //
-    (build { target = "zc706"; variant = "acpki_simple"; }) //
-    (build { target = "zc706"; variant = "acpki_master"; }) //
-    (build { target = "zc706"; variant = "acpki_satellite"; }) //
     (build { target = "zc706"; variant = "acpki_nist_clock"; }) //
     (build { target = "zc706"; variant = "acpki_nist_clock_master"; }) //
     (build { target = "zc706"; variant = "acpki_nist_clock_satellite"; }) //
diff --git a/src/Makefile b/src/Makefile
index a6a15e0f..12f33a7c 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1,5 +1,5 @@
 TARGET := zc706
-GWARGS := -V simple
+GWARGS := -V nist_clock
 
 all: ../build/runtime.bin
 
diff --git a/src/gateware/zc706.py b/src/gateware/zc706.py
index 89def338..ef442860 100755
--- a/src/gateware/zc706.py
+++ b/src/gateware/zc706.py
@@ -427,22 +427,6 @@ 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
@@ -542,21 +526,6 @@ 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)
@@ -589,8 +558,7 @@ class NIST_QC2_Satellite(_SatelliteBase, _NIST_QC2_RTIO):
         _NIST_QC2_RTIO.__init__(self)
 
 
-VARIANTS = {cls.__name__.lower(): cls for cls in [Simple, Master, Satellite, 
-                                                  NIST_CLOCK, NIST_CLOCK_Master, NIST_CLOCK_Satellite,
+VARIANTS = {cls.__name__.lower(): cls for cls in [NIST_CLOCK, NIST_CLOCK_Master, NIST_CLOCK_Satellite,
                                                   NIST_QC2, NIST_QC2_Master, NIST_QC2_Satellite]}
 
 
@@ -625,9 +593,9 @@ 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="simple",
+    parser.add_argument("-V", "--variant", default="nist_clock",
                         help="variant: "
-                             "[acpki_]simple/nist_clock/nist_qc2 "
+                             "[acpki_]nist_clock/nist_qc2[_master/_satellite] "
                              "(default: %(default)s)")
     args = parser.parse_args()