diff --git a/artiq/firmware/Cargo.lock b/artiq/firmware/Cargo.lock
index efae082ed..8ed18c45a 100644
--- a/artiq/firmware/Cargo.lock
+++ b/artiq/firmware/Cargo.lock
@@ -136,7 +136,7 @@ dependencies = [
 
 [[package]]
 name = "managed"
-version = "0.2.1"
+version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -166,7 +166,7 @@ dependencies = [
  "log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "logger_artiq 0.0.0",
  "proto 0.0.0",
- "smoltcp 0.2.1 (git+https://github.com/m-labs/smoltcp?rev=e8ece3e)",
+ "smoltcp 0.4.0-pre (git+https://github.com/m-labs/smoltcp?rev=1622244)",
  "std_artiq 0.0.0",
 ]
 
@@ -191,12 +191,12 @@ dependencies = [
 
 [[package]]
 name = "smoltcp"
-version = "0.2.1"
-source = "git+https://github.com/m-labs/smoltcp?rev=e8ece3e#e8ece3e56775f38b41906c442db320c980b98c94"
+version = "0.4.0-pre"
+source = "git+https://github.com/m-labs/smoltcp?rev=1622244#16222445a6245d29a2ffb1671a9817747676fdd7"
 dependencies = [
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
- "managed 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "managed 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -229,9 +229,9 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum libc 0.2.18 (registry+https://github.com/rust-lang/crates.io-index)" = "a51822fc847e7a8101514d1d44e354ba2ffa7d4c194dcab48870740e327cac70"
 "checksum log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)" = "ab83497bf8bf4ed2a74259c1c802351fcd67a65baa86394b6ba73c36f4838054"
 "checksum log_buffer 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ec57723b84bbe7bdf76aa93169c9b59e67473317c6de3a83cb2a0f8ccb2aa493"
-"checksum managed 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "5981b4c6de5ce272aaf2caaa56adb8f6fd24a73206b38302db572ab9374aab10"
+"checksum managed 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "61eb783b4fa77e8fa4d27ec400f97ed9168546b8b30341a120b7ba9cc6571aaf"
 "checksum rustc-cfg 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "56a596b5718bf5e059d59a30af12f7f462a152de147aa462b70892849ee18704"
-"checksum smoltcp 0.2.1 (git+https://github.com/m-labs/smoltcp?rev=e8ece3e)" = "<none>"
+"checksum smoltcp 0.4.0-pre (git+https://github.com/m-labs/smoltcp?rev=1622244)" = "<none>"
 "checksum walkdir 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "dd7c16466ecc507c7cb5988db03e6eab4aaeab89a5c37a29251fcfd3ac9b7afe"
 "checksum winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)" = "167dc9d6949a9b857f3451275e911c3f44255842c1f7a76f33c55103a909087a"
 "checksum winapi-build 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "2d315eee3b34aca4797b2da6b13ed88266e6d612562a0c46390af8299fc699bc"
diff --git a/artiq/firmware/runtime/Cargo.toml b/artiq/firmware/runtime/Cargo.toml
index 69575572f..64e73bc02 100644
--- a/artiq/firmware/runtime/Cargo.toml
+++ b/artiq/firmware/runtime/Cargo.toml
@@ -32,6 +32,6 @@ features = ["mem"]
 
 [dependencies.smoltcp]
 git = "https://github.com/m-labs/smoltcp"
-rev = "e8ece3e"
+rev = "1622244"
 default-features = false
-features = ["use_alloc", "use_collections", "use_log"]#, "verbose"]
+features = ["alloc", "collections", "log"]#, "verbose"]
diff --git a/artiq/firmware/runtime/ethmac.rs b/artiq/firmware/runtime/ethmac.rs
index b42d756fa..a2b4e281f 100644
--- a/artiq/firmware/runtime/ethmac.rs
+++ b/artiq/firmware/runtime/ethmac.rs
@@ -1,7 +1,7 @@
 use core::slice;
 use board::{csr, mem};
 use smoltcp::Error;
-use smoltcp::phy::Device;
+use smoltcp::phy::{DeviceLimits, Device};
 
 const RX0_BASE: usize = mem::ETHMAC_BASE + 0x0000;
 const RX1_BASE: usize = mem::ETHMAC_BASE + 0x0800;
@@ -23,7 +23,12 @@ impl Device for EthernetDevice {
     type RxBuffer = RxBuffer;
     type TxBuffer = TxBuffer;
 
-    fn mtu(&self) -> usize { 1500 }
+    fn limits(&self) -> DeviceLimits {
+        let mut limits = DeviceLimits::default();
+        limits.max_transmission_unit = 1500;
+        limits.max_burst_size = Some(RX_BUFFERS.len());
+        limits
+    }
 
     fn receive(&mut self) -> Result<Self::RxBuffer, Error> {
         unsafe {
diff --git a/artiq/firmware/runtime/lib.rs b/artiq/firmware/runtime/lib.rs
index a3c603c68..61e52920e 100644
--- a/artiq/firmware/runtime/lib.rs
+++ b/artiq/firmware/runtime/lib.rs
@@ -85,7 +85,7 @@ fn startup() {
     board::ad9154::init().expect("cannot initialize ad9154");
 
     let hardware_addr;
-    match config::read_str("mac", |r| r.and_then(|s| EthernetAddress::parse(s))) {
+    match config::read_str("mac", |r| r?.parse()) {
         Err(()) => {
             hardware_addr = EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]);
             warn!("using default MAC address {}; consider changing it", hardware_addr);
@@ -97,7 +97,7 @@ fn startup() {
     }
 
     let protocol_addr;
-    match config::read_str("ip", |r| r.and_then(|s| IpAddress::parse(s))) {
+    match config::read_str("ip", |r| r?.parse()) {
         Err(()) | Ok(IpAddress::Unspecified) => {
             protocol_addr = IpAddress::v4(192, 168, 1, 50);
             info!("using default IP address {}", protocol_addr);