diff --git a/default.nix b/default.nix
index fe46537..7dacea7 100644
--- a/default.nix
+++ b/default.nix
@@ -14,7 +14,7 @@ let
       version = "0.1.0";
 
       src = ./src;
-      cargoSha256 = "0d9wbki0cnpv7b62hf0pgcqhqwc8iixzl48my0rc0l0djrnmqnw0";
+      cargoSha256 = "0da6smxhlq1z739g8pdhmkfiq7b8vjqapvskz58rzklh9scf2i99";
 
       nativeBuildInputs = [
         pkgs.gnumake
diff --git a/src/Cargo.lock b/src/Cargo.lock
index 41f3f78..02f7696 100644
--- a/src/Cargo.lock
+++ b/src/Cargo.lock
@@ -201,7 +201,7 @@ dependencies = [
 [[package]]
 name = "libasync"
 version = "0.0.0"
-source = "git+https://git.m-labs.hk/M-Labs/zc706.git#b65606f2d02fab273645835a102048b23c3394f7"
+source = "git+https://git.m-labs.hk/M-Labs/zc706.git#25c6d5eeaa6243724700e975e3935a5965c09a27"
 dependencies = [
  "embedded-hal",
  "libcortex_a9",
@@ -213,7 +213,7 @@ dependencies = [
 [[package]]
 name = "libboard_zynq"
 version = "0.0.0"
-source = "git+https://git.m-labs.hk/M-Labs/zc706.git#b65606f2d02fab273645835a102048b23c3394f7"
+source = "git+https://git.m-labs.hk/M-Labs/zc706.git#25c6d5eeaa6243724700e975e3935a5965c09a27"
 dependencies = [
  "bit_field",
  "embedded-hal",
@@ -237,7 +237,7 @@ dependencies = [
 [[package]]
 name = "libcortex_a9"
 version = "0.0.0"
-source = "git+https://git.m-labs.hk/M-Labs/zc706.git#b65606f2d02fab273645835a102048b23c3394f7"
+source = "git+https://git.m-labs.hk/M-Labs/zc706.git#25c6d5eeaa6243724700e975e3935a5965c09a27"
 dependencies = [
  "bit_field",
  "libregister",
@@ -252,7 +252,7 @@ checksum = "c7d73b3f436185384286bd8098d17ec07c9a7d2388a6599f824d8502b529702a"
 [[package]]
 name = "libregister"
 version = "0.0.0"
-source = "git+https://git.m-labs.hk/M-Labs/zc706.git#b65606f2d02fab273645835a102048b23c3394f7"
+source = "git+https://git.m-labs.hk/M-Labs/zc706.git#25c6d5eeaa6243724700e975e3935a5965c09a27"
 dependencies = [
  "bit_field",
  "vcell",
@@ -262,7 +262,7 @@ dependencies = [
 [[package]]
 name = "libsupport_zynq"
 version = "0.0.0"
-source = "git+https://git.m-labs.hk/M-Labs/zc706.git#b65606f2d02fab273645835a102048b23c3394f7"
+source = "git+https://git.m-labs.hk/M-Labs/zc706.git#25c6d5eeaa6243724700e975e3935a5965c09a27"
 dependencies = [
  "compiler_builtins",
  "libboard_zynq",
diff --git a/src/runtime/src/comms.rs b/src/runtime/src/comms.rs
index 295ffb1..63b5a55 100644
--- a/src/runtime/src/comms.rs
+++ b/src/runtime/src/comms.rs
@@ -18,7 +18,7 @@ use libboard_zynq::{
     },
     timer::GlobalTimer,
 };
-use libcortex_a9::sync_channel;
+use libcortex_a9::semaphore::Semaphore;
 use futures::{select_biased, future::FutureExt};
 use libasync::{smoltcp::{Sockets, TcpStream}, task};
 
@@ -353,30 +353,25 @@ pub fn main(timer: GlobalTimer, cfg: &config::Config) {
     }
 
     task::spawn(async move {
-        let (tx, rx) = sync_channel!(u32, 1);
-        let tx = RefCell::new(tx);
-        let rx = Rc::new(RefCell::new(rx));
-        let has_connection = Rc::new(RefCell::new(false));
+        let connection = Rc::new(Semaphore::new(1, 1));
+        let terminate = Rc::new(Semaphore::new(0, 1));
         loop {
             let stream = TcpStream::accept(1381, 2048, 2048).await.unwrap();
-            let has_connection = has_connection.clone();
 
-            if *has_connection.borrow() {
-                let mut tx = tx.borrow_mut();
-                tx.async_send(42).await;
-                // the second send is used to block until another connection received the abort
-                // request.
-                tx.async_send(42).await;
+            if connection.try_wait().is_none() {
+                // there is an existing connection
+                terminate.signal();
+                connection.async_wait().await;
             }
 
-            *has_connection.borrow_mut() = true;
             let control = control.clone();
             let idle_kernel = idle_kernel.clone();
-            let _ = rx.borrow_mut().try_recv();
+            let connection = connection.clone();
+            let terminate = terminate.clone();
 
-            let new_rx = rx.clone();
+            // we make sure the value of terminate is 0 before we start
+            let _ = terminate.try_wait();
             task::spawn(async move {
-                let mut new_rx = new_rx.borrow_mut();
                 select_biased! {
                     _ = (async {
                         let _ = handle_connection(&stream, control.clone())
@@ -392,14 +387,9 @@ pub fn main(timer: GlobalTimer, cfg: &config::Config) {
                             info!("Idle kernel terminated");
                         }
                     }).fuse() => (),
-                    _ = new_rx.async_recv().fuse() => ()
+                    _ = terminate.async_wait().fuse() => ()
                 }
-                *has_connection.borrow_mut() = false;
-                // it is possible that when `handle_connection` is terminating,
-                // another connection sent an abort request and get blocked,
-                // so we try_recv here to unblock in that case.
-                let _ = new_rx.try_recv();
-                core::mem::drop(new_rx);
+                connection.signal();
                 let _ = stream.flush().await;
                 let _ = stream.abort().await;
             });
diff --git a/src/runtime/src/irq.rs b/src/runtime/src/irq.rs
index 972604f..051456d 100644
--- a/src/runtime/src/irq.rs
+++ b/src/runtime/src/irq.rs
@@ -2,6 +2,7 @@ use libboard_zynq::{gic, mpcore, println, stdio};
 use libcortex_a9::{
     asm,
     regs::{MPIDR, SP},
+    spin_lock_yield, notify_spin_lock
 };
 use libregister::{RegisterR, RegisterW};
 use core::sync::atomic::{AtomicBool, Ordering};
@@ -27,7 +28,7 @@ pub unsafe extern "C" fn IRQ() {
             SP.write(&mut __stack1_start as *mut _ as u32);
             asm::enable_irq();
             CORE1_RESTART.store(false, Ordering::Relaxed);
-            asm::sev();
+            notify_spin_lock();
             main_core1();
         }
     }
@@ -41,6 +42,6 @@ pub fn restart_core1() {
     CORE1_RESTART.store(true, Ordering::Relaxed);
     interrupt_controller.send_sgi(gic::InterruptId(0), gic::CPUCore::Core1.into());
     while CORE1_RESTART.load(Ordering::Relaxed) {
-        asm::wfe();
+        spin_lock_yield();
     }
 }