diff --git a/src/display.rs b/src/display.rs
index c03555c..4c0d912 100644
--- a/src/display.rs
+++ b/src/display.rs
@@ -82,14 +82,28 @@ impl SegmentPins {
 }
 
 #[derive(Clone, Copy, PartialEq, Eq)]
-pub struct Brightness(pub u8);
+pub struct Brightness(u8);
+
+impl Brightness {
+    pub const fn new(b: u8) -> Brightness {
+        Brightness(b)
+    }
+
+    pub const fn full() -> Brightness {
+        Brightness(u8::MAX)
+    }
+
+    pub const fn unwrap(self) -> u8 {
+        self.0
+    }
+}
 
 #[derive(Clone, Copy, PartialEq, Eq)]
 pub struct Segment(u8, Brightness);
 
 impl Segment {
     pub fn new() -> Segment {
-        Segment(0, Brightness(0xFF))
+        Segment(0, Brightness::full())
     }
 
     pub fn brightness(&mut self, b: u8) -> &mut Self {
diff --git a/src/main.rs b/src/main.rs
index e769479..f4a18a9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -12,7 +12,7 @@ use avr_device::{
     asm::sleep,
     interrupt::{CriticalSection, Mutex},
 };
-use core::cell::RefCell;
+use core::cell::{Cell, RefCell};
 use core_decimal_calc::{
     calc::{StackCalc, StackCalcError},
     Decimal,
@@ -22,8 +22,6 @@ use keyboard::{Debounce, KeyPress, KeyReadout, Keyboard};
 
 use arduino_hal::{
     adc::channel::{ADC6, ADC7},
-    hal::port::PB5,
-    port::{mode::Output, Pin},
     Adc,
 };
 use ufmt::derive::uDebug;
@@ -52,8 +50,13 @@ pub const IO_SEGMENT_RATE_US: u32 = 1000; // Time in μs between segment updates
 pub const IO_SEGMENT_ON_MIN_US: u32 = 80; // How long in μs to hold segment LEDs on (dark)
 pub const IO_SEGMENT_ON_MAX_US: u32 = 700; // How long in μs to hold segment LEDs on (bright)
 
-const fn scale_brightness(b: u8) -> u32 {
-    IO_SEGMENT_ON_MIN_US + (IO_SEGMENT_ON_MAX_US - IO_SEGMENT_ON_MIN_US) * b as u32 / 0xFF
+//TODO: When inline it is much slower due to use of Brightness instead of const 0xFF?!
+#[inline(never)]
+fn scale_brightness(b: Brightness) -> u32 {
+    assert_eq!((Brightness::full().unwrap() as u32), 0xFF);
+    IO_SEGMENT_ON_MIN_US
+        + (IO_SEGMENT_ON_MAX_US - IO_SEGMENT_ON_MIN_US) * b.unwrap() as u32
+            / (Brightness::full().unwrap() as u32)
 }
 
 // Calculator setup
@@ -67,51 +70,44 @@ type Calc = StackCalc<f32, STACK_DEPTH, 5, u8>;
 // * Set another timer to run for 1ms.
 // * On another timer interrupt expire disable display (LEDs off) and handle keyboard input.
 
-static LED: Mutex<RefCell<Option<Pin<Output, PB5>>>> = Mutex::new(RefCell::new(None));
-static IO_LOOP: Mutex<RefCell<Option<IOLoop>>> = Mutex::new(RefCell::new(None));
-static KEY_PRESS: Mutex<RefCell<Option<KeyPress>>> = Mutex::new(RefCell::new(None));
-static ADC: Mutex<RefCell<Option<Adc>>> = Mutex::new(RefCell::new(None));
-static SEGMENT_TIMER: Mutex<RefCell<Option<SegmentTimer>>> = Mutex::new(RefCell::new(None));
+// Values shared between main and interrupt handlers
+type Global<T> = Mutex<Cell<T>>;
+type RefGlobal<T> = Mutex<RefCell<Option<T>>>;
 
-fn try_access<'cs, 'v: 'cs, T, O>(
+static IO_LOOP: RefGlobal<IOLoop> = Mutex::new(RefCell::new(None));
+static KEY_PRESS: Global<Option<KeyPress>> = Mutex::new(Cell::new(None));
+static ADC: RefGlobal<Adc> = Mutex::new(RefCell::new(None));
+static SEGMENT_TIMER: RefGlobal<SegmentTimer> = Mutex::new(RefCell::new(None));
+
+fn access_global<'cs, 'v: 'cs, T, O>(
     v: &'v Mutex<RefCell<Option<T>>>,
     cs: CriticalSection<'cs>,
     f: impl for<'t> FnOnce(&'t mut T) -> O,
-) -> Option<O> {
-    if let Some(mut v) = v.borrow(cs).try_borrow_mut().ok() {
-        if let Some(v) = v.as_mut() {
-            return Some(f(v));
-        }
-    }
-    None
+) -> O {
+    let mut v = v.borrow(cs).borrow_mut();
+    f(v.as_mut().unwrap())
 }
 
 #[avr_device::interrupt(atmega328p)]
 unsafe fn TIMER0_COMPA() {
     avr_device::interrupt::free(|cs| {
-        // try_access(&LED, cs, |led| led.set_high()).expect("LED not available (COMPA)");
-        let brightness = try_access(&IO_LOOP, cs, |io_loop| io_loop.display_on());
-        if let Some(brightness) = brightness {
-            try_access(&SEGMENT_TIMER, cs, |st| {
-                st.segment_on_time(scale_brightness(brightness.0))
-            });
-        }
+        let brightness = access_global(&IO_LOOP, cs, |io_loop| io_loop.display_on());
+        access_global(&SEGMENT_TIMER, cs, |st| {
+            st.segment_on_time(scale_brightness(brightness))
+        });
     });
 }
 
 #[avr_device::interrupt(atmega328p)]
 unsafe fn TIMER0_COMPB() {
     avr_device::interrupt::free(|cs| {
-        // try_access(&LED, cs, |led| led.set_low()).expect("LED not available (COMPB)");
-        try_access(&IO_LOOP, cs, |io_loop| {
+        access_global(&IO_LOOP, cs, |io_loop| {
             io_loop.display_off();
-            try_access(&ADC, cs, |adc| {
+            access_global(&ADC, cs, |adc| {
                 io_loop.read_key(adc);
             });
             if let Some(key) = io_loop.advance() {
-                if let Some(mut key_press) = KEY_PRESS.borrow(cs).try_borrow_mut().ok() {
-                    key_press.replace(key);
-                }
+                KEY_PRESS.borrow(cs).replace(Some(key));
             }
         });
     });
@@ -522,7 +518,6 @@ fn main() -> ! {
     );
     let keyboard = Keyboard::new(ADC7, ADC6);
     let io_loop = IOLoop::new(io_pins, segment_pins, keyboard);
-    let led = pins.d13.into_output();
     let adc = Adc::new(dp.ADC, Default::default());
     let segment_timer = SegmentTimer::init(dp.TC0, IO_SEGMENT_RATE_US);
 
@@ -538,7 +533,6 @@ fn main() -> ! {
     };
 
     avr_device::interrupt::free(|cs| {
-        LED.borrow(cs).replace(Some(led));
         IO_LOOP.borrow(cs).replace(Some(io_loop));
         ADC.borrow(cs).replace(Some(adc));
         SEGMENT_TIMER.borrow(cs).replace(Some(segment_timer));
@@ -550,7 +544,7 @@ fn main() -> ! {
     loop {
         let mut key = None;
         avr_device::interrupt::free(|cs| {
-            key = KEY_PRESS.borrow(cs).borrow_mut().take();
+            key = KEY_PRESS.borrow(cs).take();
         });
 
         if let TransientState::Done = state.transient {
@@ -611,14 +605,16 @@ fn main() -> ! {
                     seg.dp();
                 }
                 for (no, seg) in display.slice(0, DISPLAY_SEGMENTS).iter_mut().enumerate() {
-                    seg.brightness((no * 0xFF / DISPLAY_SEGMENTS) as u8);
+                    seg.brightness(
+                        (no * (Brightness::full().unwrap() as usize) / DISPLAY_SEGMENTS) as u8,
+                    );
                 }
             }
             TransientState::Err { .. } => display.error(),
         }
 
         avr_device::interrupt::free(|cs| {
-            try_access(&IO_LOOP, cs, |io_loop| {
+            access_global(&IO_LOOP, cs, |io_loop| {
                 io_loop.update_display(&display);
             });
         });
diff --git a/src/timer.rs b/src/timer.rs
index ef5be87..8885aa8 100644
--- a/src/timer.rs
+++ b/src/timer.rs
@@ -5,10 +5,6 @@ const TIMER_PRESCALE: u32 = 64;
 // Timer clock tick rate per second
 const TIMER_FREQ: u32 = DefaultClock::FREQ / TIMER_PRESCALE;
 
-// How much time in μs to reserve for post LED off operation (keyboard read)
-const BUFFER_US: u32 = 250;
-const BUFFER_TICKS: u32 = us_to_ticks(BUFFER_US);
-
 const fn us_to_ticks(us: u32) -> u32 {
     TIMER_FREQ * us / 1_000_000
 }
@@ -46,12 +42,7 @@ impl SegmentTimer {
     // Set for how long the segment LEDs should be on in μs
     // Controls TIMER0_COMPB interrupt time after TIMER0_COMPA
     pub fn segment_on_time(&mut self, segment_on_us: u32) {
-        let ocra = self.0.ocr0a.read().bits();
         let ocrb = us_to_ticks(segment_on_us);
-        assert!(
-            ocra as u32 > ocrb + BUFFER_TICKS,
-            "segment_on_us cannot be longer than segment_switch_us - buffer"
-        );
         // Set the compare value for B match
         self.0.ocr0b.write(|w| {
             w.bits(