diff --git a/artiq/firmware/Cargo.lock b/artiq/firmware/Cargo.lock
index 6ef0db1fb..0d7220265 100644
--- a/artiq/firmware/Cargo.lock
+++ b/artiq/firmware/Cargo.lock
@@ -157,7 +157,7 @@ dependencies = [
  "log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "logger_artiq 0.0.0",
  "proto 0.0.0",
- "smoltcp 0.4.0-pre (git+https://github.com/m-labs/smoltcp?rev=bc2a894)",
+ "smoltcp 0.4.0-pre (git+https://github.com/m-labs/smoltcp?rev=b927085)",
  "std_artiq 0.0.0",
 ]
 
@@ -183,7 +183,7 @@ dependencies = [
 [[package]]
 name = "smoltcp"
 version = "0.4.0-pre"
-source = "git+https://github.com/m-labs/smoltcp?rev=bc2a894#bc2a894c00c9e0cbc51d67c01f456e45b45abcc2"
+source = "git+https://github.com/m-labs/smoltcp?rev=b927085#b92708596a09ff58c341be6bf42b38b00cc44657"
 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)",
@@ -221,7 +221,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum log_buffer 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ec57723b84bbe7bdf76aa93169c9b59e67473317c6de3a83cb2a0f8ccb2aa493"
 "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 0.4.0-pre (git+https://github.com/m-labs/smoltcp?rev=bc2a894)" = "<none>"
+"checksum smoltcp 0.4.0-pre (git+https://github.com/m-labs/smoltcp?rev=b927085)" = "<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 069a8da1f..814120c19 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 = "bc2a894"
+rev = "b927085"
 default-features = false
 features = ["alloc", "collections", "log"]#, "verbose"]
diff --git a/artiq/firmware/runtime/lib.rs b/artiq/firmware/runtime/lib.rs
index f679eba28..af469147b 100644
--- a/artiq/firmware/runtime/lib.rs
+++ b/artiq/firmware/runtime/lib.rs
@@ -106,14 +106,15 @@ fn startup() {
         }
     }
 
-    fn _net_trace_writer<U>(printer: smoltcp::wire::PrettyPrinter<U>)
-            where U: smoltcp::wire::pretty_print::PrettyPrint {
-        print!("\x1b[37m{}\x1b[0m", printer)
-    }
+    // fn _net_trace_writer<U>(timestamp: u64, printer: smoltcp::wire::PrettyPrinter<U>)
+    //         where U: smoltcp::wire::pretty_print::PrettyPrint {
+    //     let seconds = timestamp / 1000;
+    //     let micros  = timestamp % 1000 * 1000;
+    //     print!("\x1b[37m[{:6}.{:06}s]\n{}\x1b[0m", seconds, micros, printer)
+    // }
 
     let net_device = ethmac::EthernetDevice;
-    // let net_device = smoltcp::phy::Tracer::<_, smoltcp::wire::EthernetFrame<&[u8]>>
-    //                                      ::new(net_device, _net_trace_writer);
+    // let net_device = smoltcp::phy::EthernetTracer::new(net_device, _net_trace_writer);
     let arp_cache  = smoltcp::iface::SliceArpCache::new([Default::default(); 8]);
     let mut interface  = smoltcp::iface::EthernetInterface::new(
         Box::new(net_device), Box::new(arp_cache) as Box<smoltcp::iface::ArpCache>,
@@ -156,10 +157,9 @@ fn startup() {
 
         match interface.poll(&mut *borrow_mut!(scheduler.sockets()),
                              board::clock::get_ms()) {
-            Ok(()) => (),
-            Err(smoltcp::Error::Exhausted) => (),
+            Ok(_poll_at) => (),
             Err(smoltcp::Error::Unrecognized) => (),
-            Err(e) => warn!("network error: {}", e)
+            Err(err) => warn!("network error: {}", err)
         }
     }
 }