diff --git a/src/runtime/src/si5324.rs b/src/runtime/src/si5324.rs
index 48ce207..dbd301d 100644
--- a/src/runtime/src/si5324.rs
+++ b/src/runtime/src/si5324.rs
@@ -271,3 +271,75 @@ pub fn select_input(i2c: &mut I2c, input: Input, timer: GlobalTimer) -> Result<(
     monitor_lock(i2c, timer)?;
     Ok(())
 }
+
+#[cfg(has_siphaser)]
+pub mod siphaser {
+    use super::*;
+    use pl::csr;
+
+    pub fn select_recovered_clock(i2c: &mut I2c, rc: bool, timer: GlobalTimer) -> Result<()> {
+        write(i2c, 3,   (read(3)? & 0xdf) | (1 << 5))?;  // DHOLD=1
+        unsafe {
+            csr::siphaser::switch_clocks_write(if rc { 1 } else { 0 });
+        }
+        write(i2c, 3,   (read(3)? & 0xdf) | (0 << 5))?;  // DHOLD=0
+        monitor_lock(timer)?;
+        Ok(())
+    }
+
+    fn phase_shift(direction: u8, timer: GlobalTimer) {
+        unsafe {
+            csr::siphaser::phase_shift_write(direction);
+            while csr::siphaser::phase_shift_done_read() == 0 {}
+        }
+        // wait for the Si5324 loop to stabilize
+        timer.delay_us(500);
+    }
+
+    fn has_error(timer: GlobalTimer) -> bool {
+        unsafe {
+            csr::siphaser::error_write(1);
+        }
+        timer.delay_us(5_000);
+        unsafe {
+            csr::siphaser::error_read() != 0
+        }
+    }
+
+    fn find_edge(target: bool, timer: GlobalTimer) -> Result<u32> {
+        let mut nshifts = 0;
+
+        let mut previous = has_error(timer);
+        loop {
+            phase_shift(1, timer);
+            nshifts += 1;
+            let current = has_error(timer);
+            if previous != target && current == target {
+                return Ok(nshifts);
+            }
+            if nshifts > 5000 {
+                return Err("failed to find timing error edge");
+            }
+            previous = current;
+        }
+    }
+
+    pub fn calibrate_skew(timer: GlobalTimer) -> Result<()> {
+        let jitter_margin = 32;
+        let lead = find_edge(false, timer)?;
+        for _ in 0..jitter_margin {
+            phase_shift(1, timer);
+        }
+        let width = find_edge(true, timer)? + jitter_margin;
+        // width is 360 degrees (one full rotation of the phase between s/h limits) minus jitter
+        info!("calibration successful, lead: {}, width: {} ({}deg)", lead, width, width*360/(56*8));
+
+        // Apply reverse phase shift for half the width to get into the
+        // middle of the working region.
+        for _ in 0..width/2 {
+            phase_shift(0, timer);
+        }
+
+        Ok(())
+    }
+}