diff --git a/crate/bcm2837/src/gpio.rs b/crate/bcm2837/src/gpio.rs
index aa2f9ef..4465303 100644
--- a/crate/bcm2837/src/gpio.rs
+++ b/crate/bcm2837/src/gpio.rs
@@ -116,8 +116,12 @@ impl Gpio<Uninitialized> {
     /// Enables the alternative function `function` for `self`. Consumes self
     /// and returns a `Gpio` structure in the `Alt` state.
     pub fn into_alt(self, function: Function) -> Gpio<Alt> {
-        self.registers.FSEL[(self.pin / 10) as usize]
-            .write((function as u32) << (3 * (self.pin % 10)));
+        let select = (self.pin / 10) as usize;
+        let offset = 3 * (self.pin % 10) as usize;
+        let mut value = self.registers.FSEL[select].read();
+        value &= !(0b111 << offset);
+        value |= (function as u32) << offset;
+        self.registers.FSEL[select].write(value);
         self.transition()
     }
 
diff --git a/kernel/src/arch/aarch64/board/raspi3/mod.rs b/kernel/src/arch/aarch64/board/raspi3/mod.rs
index bdd0b21..3ff2324 100644
--- a/kernel/src/arch/aarch64/board/raspi3/mod.rs
+++ b/kernel/src/arch/aarch64/board/raspi3/mod.rs
@@ -5,9 +5,12 @@ extern crate bcm2837;
 pub mod serial;
 
 pub fn init() {
-    assert_has_not_been_called!("board::init must be called only once");
+    // FIXME
+    // assert_has_not_been_called!("board::init must be called only once");
 
-    serial::SERIAL_PORT.lock().init();
+    unsafe {
+        serial::SERIAL_PORT.init();
+    }
 
     println!("Hello Raspberry Pi!");
 }
diff --git a/kernel/src/arch/aarch64/board/raspi3/serial.rs b/kernel/src/arch/aarch64/board/raspi3/serial.rs
index b6c29f7..5434071 100644
--- a/kernel/src/arch/aarch64/board/raspi3/serial.rs
+++ b/kernel/src/arch/aarch64/board/raspi3/serial.rs
@@ -20,7 +20,8 @@ impl SerialPort {
 
     /// Init a newly created SerialPort, can only be called once.
     pub fn init(&mut self) {
-        assert_has_not_been_called!("SerialPort::init must be called only once");
+        // FIXME
+        // assert_has_not_been_called!("SerialPort::init must be called only once");
         self.mu = Some(MiniUart::new());
     }
 
@@ -70,4 +71,7 @@ impl fmt::Write for SerialPort {
     }
 }
 
-pub static SERIAL_PORT: Mutex<SerialPort> = Mutex::new(SerialPort::new());
+// FIXME
+// pub static SERIAL_PORT: Mutex<SerialPort> = Mutex::new(SerialPort::new());
+pub static mut SERIAL_PORT: SerialPort = SerialPort::new();
+
diff --git a/kernel/src/arch/aarch64/io.rs b/kernel/src/arch/aarch64/io.rs
index 5e5a645..deda39c 100644
--- a/kernel/src/arch/aarch64/io.rs
+++ b/kernel/src/arch/aarch64/io.rs
@@ -4,9 +4,15 @@ use core::fmt::{Arguments, Write};
 use super::board::serial::{SerialRead, SERIAL_PORT};
 
 pub fn getchar() -> char {
-    SERIAL_PORT.lock().receive() as char
+    // FIXME
+    unsafe {
+        SERIAL_PORT.receive() as char
+    }
 }
 
 pub fn putfmt(fmt: Arguments) {
-    SERIAL_PORT.lock().write_fmt(fmt).unwrap()
+    // FIXME
+    unsafe {
+        SERIAL_PORT.write_fmt(fmt).unwrap()
+    }
 }
diff --git a/kernel/src/arch/aarch64/mod.rs b/kernel/src/arch/aarch64/mod.rs
index ac14adb..f668a25 100644
--- a/kernel/src/arch/aarch64/mod.rs
+++ b/kernel/src/arch/aarch64/mod.rs
@@ -17,7 +17,8 @@ pub extern "C" fn rust_main() -> ! {
     board::init();
 
     // First init log mod, so that we can print log info.
-    ::logging::init();
+    // FIXME
+    // ::logging::init();
 
     super::fs::show_logo();