diff --git a/src/Cargo.lock b/src/Cargo.lock
index 3217e60..d42c75c 100644
--- a/src/Cargo.lock
+++ b/src/Cargo.lock
@@ -187,7 +187,7 @@ dependencies = [
 [[package]]
 name = "libasync"
 version = "0.0.0"
-source = "git+https://git.m-labs.hk/M-Labs/zynq-rs.git#a73df780d0d0e757738f27feac162904f5bf93f9"
+source = "git+https://git.m-labs.hk/M-Labs/zynq-rs.git#157439bc88cbb18bb40009428acf1fdee800e32e"
 dependencies = [
  "embedded-hal",
  "libcortex_a9",
@@ -199,7 +199,7 @@ dependencies = [
 [[package]]
 name = "libboard_zynq"
 version = "0.0.0"
-source = "git+https://git.m-labs.hk/M-Labs/zynq-rs.git#a73df780d0d0e757738f27feac162904f5bf93f9"
+source = "git+https://git.m-labs.hk/M-Labs/zynq-rs.git#157439bc88cbb18bb40009428acf1fdee800e32e"
 dependencies = [
  "bit_field",
  "embedded-hal",
@@ -233,7 +233,7 @@ dependencies = [
 [[package]]
 name = "libcortex_a9"
 version = "0.0.0"
-source = "git+https://git.m-labs.hk/M-Labs/zynq-rs.git#a73df780d0d0e757738f27feac162904f5bf93f9"
+source = "git+https://git.m-labs.hk/M-Labs/zynq-rs.git#157439bc88cbb18bb40009428acf1fdee800e32e"
 dependencies = [
  "bit_field",
  "libregister",
@@ -249,7 +249,7 @@ checksum = "c7d73b3f436185384286bd8098d17ec07c9a7d2388a6599f824d8502b529702a"
 [[package]]
 name = "libregister"
 version = "0.0.0"
-source = "git+https://git.m-labs.hk/M-Labs/zynq-rs.git#a73df780d0d0e757738f27feac162904f5bf93f9"
+source = "git+https://git.m-labs.hk/M-Labs/zynq-rs.git#157439bc88cbb18bb40009428acf1fdee800e32e"
 dependencies = [
  "bit_field",
  "vcell",
@@ -259,7 +259,7 @@ dependencies = [
 [[package]]
 name = "libsupport_zynq"
 version = "0.0.0"
-source = "git+https://git.m-labs.hk/M-Labs/zynq-rs.git#a73df780d0d0e757738f27feac162904f5bf93f9"
+source = "git+https://git.m-labs.hk/M-Labs/zynq-rs.git#157439bc88cbb18bb40009428acf1fdee800e32e"
 dependencies = [
  "compiler_builtins",
  "libboard_zynq",
diff --git a/src/Cargo.toml b/src/Cargo.toml
index e68c9bd..4bc1f76 100644
--- a/src/Cargo.toml
+++ b/src/Cargo.toml
@@ -24,7 +24,7 @@ overflow-checks = false
 panic = "abort"
 debug = true
 codegen-units = 1
-opt-level = 's'
+opt-level = 2
 lto = true
 
 [patch.crates-io]
diff --git a/src/runtime/src/kernel/control.rs b/src/runtime/src/kernel/control.rs
index 91fefa3..3ffe131 100644
--- a/src/runtime/src/kernel/control.rs
+++ b/src/runtime/src/kernel/control.rs
@@ -1,7 +1,7 @@
 use libcortex_a9::sync_channel::{Sender, Receiver};
 use libsupport_zynq::boot::Core1;
 
-use super::{CHANNEL_0TO1, CHANNEL_1TO0, INIT_LOCK, Message};
+use super::{CHANNEL_0TO1, CHANNEL_1TO0, CHANNEL_SEM, INIT_LOCK, Message};
 use crate::irq::restart_core1;
 
 use core::mem::{forget, replace};
@@ -12,6 +12,7 @@ pub struct Control {
 }
 
 fn get_channels() -> (Sender<'static, Message>, Receiver<'static, Message>) {
+    CHANNEL_SEM.wait();
     let mut core0_tx = None;
     while core0_tx.is_none() {
         core0_tx = CHANNEL_0TO1.lock().take();
diff --git a/src/runtime/src/kernel/core1.rs b/src/runtime/src/kernel/core1.rs
index ec2e27c..94e0e24 100644
--- a/src/runtime/src/kernel/core1.rs
+++ b/src/runtime/src/kernel/core1.rs
@@ -20,6 +20,7 @@ use super::{
     rpc::rpc_send_async,
     INIT_LOCK,
     CHANNEL_0TO1, CHANNEL_1TO0,
+    CHANNEL_SEM,
     KERNEL_CHANNEL_0TO1, KERNEL_CHANNEL_1TO0,
     KERNEL_IMAGE,
     Message,
@@ -159,6 +160,7 @@ pub fn main_core1() {
     }
     *CHANNEL_0TO1.lock() = Some(core0_tx);
     *CHANNEL_1TO0.lock() = Some(core0_rx);
+    CHANNEL_SEM.signal();
 
     // set on load, cleared on start
     let mut loaded_kernel = None;
diff --git a/src/runtime/src/kernel/mod.rs b/src/runtime/src/kernel/mod.rs
index e06a6e1..c3bb1fb 100644
--- a/src/runtime/src/kernel/mod.rs
+++ b/src/runtime/src/kernel/mod.rs
@@ -1,7 +1,7 @@
 use core::ptr;
 use alloc::{vec::Vec, string::String};
 
-use libcortex_a9::{mutex::Mutex, sync_channel};
+use libcortex_a9::{mutex::Mutex, sync_channel, semaphore::Semaphore};
 use crate::eh_artiq;
 
 mod control;
@@ -48,6 +48,7 @@ pub enum Message {
 
 static CHANNEL_0TO1: Mutex<Option<sync_channel::Sender<'static, Message>>> = Mutex::new(None);
 static CHANNEL_1TO0: Mutex<Option<sync_channel::Receiver<'static, Message>>> = Mutex::new(None);
+static CHANNEL_SEM: Semaphore = Semaphore::new(0, 1);
 
 static mut KERNEL_CHANNEL_0TO1: Option<sync_channel::Receiver<'static, Message>> = None;
 static mut KERNEL_CHANNEL_1TO0: Option<sync_channel::Sender<'static, Message>> = None;