diff --git a/src/gateware/wrpll.py b/src/gateware/wrpll.py
index e6f9ceb..e3b3f63 100644
--- a/src/gateware/wrpll.py
+++ b/src/gateware/wrpll.py
@@ -137,7 +137,7 @@ class SMA_PLL(Module, AutoCSR):
         self.clock_domains.cd_ref = ClockDomain()
 
         self.mmcm_locked = CSRStatus()
-        self.mmcm_reset = CSRStorage() #TODO for i_RST
+        self.mmcm_reset = CSRStorage()
 
         self.drp_addr = CSRStorage(7)
         self.drp_in = CSRStorage(16)
@@ -154,10 +154,10 @@ class SMA_PLL(Module, AutoCSR):
             Instance("MMCME2_ADV",
                 p_BANDWIDTH="LOW",  # lower jitter
                 o_LOCKED=self.mmcm_locked.status,
+                i_RST=self.mmcm_reset.storage,
                 
                 p_CLKIN1_PERIOD=period,
                 i_CLKIN1=ClockSignal("sys"),
-                i_RST=ResetSignal("sys"),
                 i_CLKINSEL=1,  # 1=CLKIN1 0=CLKIN2
 
                 # VCO @ 1Ghz
@@ -184,4 +184,3 @@ class SMA_PLL(Module, AutoCSR):
             # debug output
             Instance("OBUFDS", i_I=self.cd_ref.clk, o_O=sma_clkin.p, o_OB=sma_clkin.n)
         ]
-
diff --git a/src/libboard_artiq/src/si549.rs b/src/libboard_artiq/src/si549.rs
index 1227ff9..5c64597 100644
--- a/src/libboard_artiq/src/si549.rs
+++ b/src/libboard_artiq/src/si549.rs
@@ -556,6 +556,20 @@ pub mod sma_pll {
 
         use super::*;
 
+        pub struct MmcmSetting {
+            pub clkout0_reg1: u16,  //0x08
+            pub clkout0_reg2: u16,  //0x09
+            pub clkfbout_reg1: u16, //0x14
+            pub clkfbout_reg2: u16, //0x15
+            pub div_reg: u16,       //0x16
+            pub lock_reg1: u16,     //0x18
+            pub lock_reg2: u16,     //0x19
+            pub lock_reg3: u16,     //0x1A
+            pub power_reg: u16,     //0x28
+            pub filt_reg1: u16,     //0x4E
+            pub filt_reg2: u16,     //0x4F
+        }
+
         fn one_clock_cycle(timer: &mut GlobalTimer) {
             unsafe {
                 csr::sma_pll::drp_clk_write(1);
@@ -600,7 +614,6 @@ pub mod sma_pll {
         }
 
         pub fn read(timer: &mut GlobalTimer, address: u8) -> u16 {
-            // Based on "DRP State Machine" from XAPP888
             set_addr(address);
             set_enable(true);
             // Set DADDR on the MMCM and assert DEN for one clock cycle
@@ -615,7 +628,6 @@ pub mod sma_pll {
         }
 
         pub fn write(timer: &mut GlobalTimer, address: u8, value: u16) {
-            // Based on "DRP State Machine" from XAPP888
             set_addr(address);
             set_data(value);
             set_write_enable(true);
@@ -630,6 +642,41 @@ pub mod sma_pll {
                 one_clock_cycle(timer);
             }
         }
+
+        pub fn reset(rst: bool) {
+            unsafe {
+                let val = if rst { 1 } else { 0 };
+                csr::sma_pll::mmcm_reset_write(val)
+            }
+        }
+
+        pub fn setup(timer: &mut GlobalTimer, settings: MmcmSetting) -> Result<(), &'static str> {
+            // Based on "DRP State Machine" from XAPP888
+
+            // hold reset HIGH during mmcm config
+            reset(true);
+            write(timer, 0x08, settings.clkout0_reg1);
+            write(timer, 0x09, settings.clkout0_reg2);
+            write(timer, 0x14, settings.clkfbout_reg1);
+            write(timer, 0x15, settings.clkfbout_reg2);
+            write(timer, 0x16, settings.div_reg);
+            write(timer, 0x18, settings.lock_reg1);
+            write(timer, 0x19, settings.lock_reg2);
+            write(timer, 0x1A, settings.lock_reg3);
+            write(timer, 0x28, settings.power_reg);
+            write(timer, 0x4E, settings.filt_reg1);
+            write(timer, 0x4F, settings.filt_reg2);
+            reset(false);
+
+            // wait for the mmcm to lock
+            timer.delay_us(100);
+
+            let locked = unsafe { csr::sma_pll::mmcm_locked_read() == 1 };
+            if !locked {
+                return Err("failed to generate 125Mhz ref clock from SMA CLKIN");
+            }
+            Ok(())
+        }
     }
 
     pub fn setup(timer: &mut GlobalTimer) {