diff --git a/artiq/firmware/libboard/Cargo.toml b/artiq/firmware/libboard/Cargo.toml
index 9604e9a6e..be1129200 100644
--- a/artiq/firmware/libboard/Cargo.toml
+++ b/artiq/firmware/libboard/Cargo.toml
@@ -15,5 +15,11 @@ build_misoc = { path = "../libbuild_misoc" }
 [dependencies]
 byteorder = { version = "1.0", default-features = false }
 
+[dependencies.smoltcp]
+git = "https://github.com/m-labs/smoltcp"
+rev = "507d2fe"
+default-features = false
+optional = true
+
 [features]
 uart_console = []
diff --git a/artiq/firmware/runtime/ethmac.rs b/artiq/firmware/libboard/ethmac.rs
similarity index 97%
rename from artiq/firmware/runtime/ethmac.rs
rename to artiq/firmware/libboard/ethmac.rs
index a19a13933..1a1f29272 100644
--- a/artiq/firmware/runtime/ethmac.rs
+++ b/artiq/firmware/libboard/ethmac.rs
@@ -2,7 +2,8 @@ use core::{slice, fmt};
 use smoltcp::Result;
 use smoltcp::phy::{self, DeviceCapabilities, Device};
 
-use board::{csr, mem};
+use csr;
+use mem::ETHMAC_BASE;
 
 const RX_SLOTS: usize = csr::ETHMAC_RX_SLOTS as usize;
 const TX_SLOTS: usize = csr::ETHMAC_TX_SLOTS as usize;
@@ -30,12 +31,12 @@ fn next_tx_slot() -> Option<usize> {
 
 fn rx_buffer(slot: usize) -> *const u8 {
     debug_assert!(slot < RX_SLOTS);
-    (mem::ETHMAC_BASE + SLOT_SIZE * slot) as _
+    (ETHMAC_BASE + SLOT_SIZE * slot) as _
 }
 
 fn tx_buffer(slot: usize) -> *mut u8 {
     debug_assert!(slot < TX_SLOTS);
-    (mem::ETHMAC_BASE + SLOT_SIZE * (RX_SLOTS + slot)) as _
+    (ETHMAC_BASE + SLOT_SIZE * (RX_SLOTS + slot)) as _
 }
 
 pub struct EthernetDevice(());
diff --git a/artiq/firmware/libboard/lib.rs b/artiq/firmware/libboard/lib.rs
index 27de0b9e1..06e08a417 100644
--- a/artiq/firmware/libboard/lib.rs
+++ b/artiq/firmware/libboard/lib.rs
@@ -2,6 +2,8 @@
 #![feature(asm)]
 
 extern crate byteorder;
+#[cfg(feature = "smoltcp")]
+extern crate smoltcp;
 
 #[cfg(target_arch = "or1k")]
 #[path = "or1k/mod.rs"]
@@ -21,3 +23,5 @@ pub mod spiflash;
 pub mod config;
 #[cfg(feature = "uart_console")]
 pub mod uart_console;
+#[cfg(all(has_ethmac, feature = "smoltcp"))]
+pub mod ethmac;
diff --git a/artiq/firmware/runtime/Cargo.toml b/artiq/firmware/runtime/Cargo.toml
index 5802b84b2..f9d75b567 100644
--- a/artiq/firmware/runtime/Cargo.toml
+++ b/artiq/firmware/runtime/Cargo.toml
@@ -17,7 +17,7 @@ build_artiq = { path = "../libbuild_artiq" }
 byteorder = { version = "1.0", default-features = false }
 cslice = { version = "0.3" }
 log = { version = "0.3", default-features = false }
-board = { path = "../libboard", features = ["uart_console"] }
+board = { path = "../libboard", features = ["uart_console", "smoltcp"] }
 alloc_list = { path = "../liballoc_list" }
 std_artiq = { path = "../libstd_artiq", features = ["alloc", "io_error_alloc"] }
 logger_artiq = { path = "../liblogger_artiq" }
diff --git a/artiq/firmware/runtime/main.rs b/artiq/firmware/runtime/main.rs
index d5e9462f5..245acb8ba 100644
--- a/artiq/firmware/runtime/main.rs
+++ b/artiq/firmware/runtime/main.rs
@@ -26,11 +26,11 @@ extern crate drtioaux;
 use smoltcp::wire::{EthernetAddress, IpAddress, IpCidr};
 
 use board::config;
+#[cfg(has_ethmac)]
+use board::ethmac;
 use proto::{mgmt_proto, analyzer_proto, moninj_proto, rpc_proto, session_proto, kernel_proto};
 use amp::{mailbox, rpc_queue};
 
-#[cfg(has_ethmac)]
-mod ethmac;
 #[cfg(has_rtio_core)]
 mod rtio_mgt;