diff --git a/artiq/firmware/libboard/lib.rs b/artiq/firmware/libboard/lib.rs
index edeef1e69..738740273 100644
--- a/artiq/firmware/libboard/lib.rs
+++ b/artiq/firmware/libboard/lib.rs
@@ -25,6 +25,8 @@ pub mod spi;
 #[cfg(has_si5324)]
 pub mod si5324;
 
+#[cfg(has_serwb_phy)]
+pub mod serwb;
 #[cfg(has_ad9516)]
 #[allow(dead_code)]
 mod ad9516_reg;
diff --git a/artiq/firmware/libboard/serwb.rs b/artiq/firmware/libboard/serwb.rs
new file mode 100644
index 000000000..ce7fbf2cf
--- /dev/null
+++ b/artiq/firmware/libboard/serwb.rs
@@ -0,0 +1,18 @@
+use csr;
+
+pub fn wait_init() {
+    info!("waiting for AMC/RTM serwb bridge to be ready...");
+    unsafe {
+        while csr::serwb_phy::control_ready_read() != 0 {}
+    }
+    info!("done.");
+
+    // Try reading the identifier register on the other side of the bridge.
+    let rtm_identifier = unsafe {
+        csr::rtm_identifier::identifier_read()
+    };
+    if rtm_identifier != 0x5352544d {
+        error!("incorrect RTM identifier: 0x{:08x}", rtm_identifier);
+        // proceed anyway
+    }
+}
diff --git a/artiq/firmware/runtime/lib.rs b/artiq/firmware/runtime/lib.rs
index 80b780497..e09cf321d 100644
--- a/artiq/firmware/runtime/lib.rs
+++ b/artiq/firmware/runtime/lib.rs
@@ -63,6 +63,9 @@ fn startup() {
     info!("software version {}", include_str!(concat!(env!("OUT_DIR"), "/git-describe")));
     info!("gateware version {}", board::ident(&mut [0; 64]));
 
+    #[cfg(has_serwb_phy)]
+    board::serwb::wait_init();
+
     let t = board::clock::get_ms();
     info!("press 'e' to erase startup and idle kernels...");
     while board::clock::get_ms() < t + 1000 {
diff --git a/artiq/firmware/satman/lib.rs b/artiq/firmware/satman/lib.rs
index 3137e7e04..95fbb6e59 100644
--- a/artiq/firmware/satman/lib.rs
+++ b/artiq/firmware/satman/lib.rs
@@ -195,6 +195,9 @@ fn startup() {
     info!("software version {}", include_str!(concat!(env!("OUT_DIR"), "/git-describe")));
     info!("gateware version {}", board::ident(&mut [0; 64]));
 
+    #[cfg(has_serwb_phy)]
+    board::serwb::wait_init();
+
     #[cfg(has_ad9516)]
     board::ad9516::init().expect("cannot initialize AD9516");
     #[cfg(has_hmc830_7043)]