diff --git a/artiq/firmware/runtime/main.rs b/artiq/firmware/runtime/main.rs
index bb18e7dbf..4e4011e40 100644
--- a/artiq/firmware/runtime/main.rs
+++ b/artiq/firmware/runtime/main.rs
@@ -110,7 +110,20 @@ fn startup() {
 #[cfg(si5324_free_running)]
 fn setup_si5324_free_running()
 {
-    // 150MHz output (hardcoded)
+    // 125MHz output, from 10MHz CLKIN2 reference
+    #[cfg(all(rtio_frequency = "125.0", si5324_ext_ref))]
+    const SI5324_SETTINGS: board_artiq::si5324::FrequencySettings
+        = board_artiq::si5324::FrequencySettings {
+        n1_hs  : 10,
+        nc1_ls : 4,
+        n2_hs  : 10,
+        n2_ls  : 300,
+        n31    : 75,
+        n32    : 6,
+        bwsel  : 10
+    };
+    // 150MHz output, from crystal
+    #[cfg(all(rtio_frequency = "150.0", not(si5324_ext_ref)))]
     const SI5324_SETTINGS: board_artiq::si5324::FrequencySettings
         = board_artiq::si5324::FrequencySettings {
         n1_hs  : 9,
diff --git a/artiq/gateware/targets/kasli.py b/artiq/gateware/targets/kasli.py
index 7684a8f1b..72b147064 100755
--- a/artiq/gateware/targets/kasli.py
+++ b/artiq/gateware/targets/kasli.py
@@ -104,6 +104,8 @@ class _StandaloneBase(MiniSoC, AMPSoC):
         self.submodules.i2c = gpio.GPIOTristate([i2c.scl, i2c.sda])
         self.csr_devices.append("i2c")
         self.config["I2C_BUS_COUNT"] = 1
+        self.config["HAS_SI5324"] = None
+        self.config["SI5324_SOFT_RESET"] = None
 
     def add_rtio(self, rtio_channels):
         self.submodules.rtio_crg = _RTIOCRG(self.platform, self.crg.cd_sys.clk)
@@ -227,6 +229,10 @@ class Opticlock(_StandaloneBase):
     def __init__(self, **kwargs):
         _StandaloneBase.__init__(self, **kwargs)
 
+        self.config["SI5324_FREE_RUNNING"] = None
+        self.config["SI5324_EXT_REF"] = None
+        self.config["RTIO_FREQUENCY"] = "125.0"
+
         platform = self.platform
         platform.add_extension(_dio("eem0"))
         platform.add_extension(_dio("eem1"))
@@ -318,6 +324,7 @@ class Master(MiniSoC, AMPSoC):
         self.config["HAS_SI5324"] = None
         self.config["SI5324_SOFT_RESET"] = None
         self.config["SI5324_FREE_RUNNING"] = None
+        self.config["RTIO_FREQUENCY"] = str(rtio_clk_freq/1e6)
 
         self.comb += platform.request("sfp_ctl", 2).tx_disable.eq(0)
         self.submodules.transceiver = gtp_7series.GTP(