got to idle state waiting for key

Cargo.lock

@@ -36,6 +36,7 @@ name = "avr-calc"
 version = "0.1.0"
 dependencies = [
  "arduino-hal",
+ "avr-device",
  "calc-math",
  "embedded-hal 1.0.0",
  "nb 1.1.0",

Cargo.toml

@@ -15,6 +15,7 @@ ufmt = "0.2.0"
 nb = "1.1.0"
 embedded-hal = "1.0"
 calc-math = { path = "../calc-math", features = ["ufmt"] }
+avr-device = "0.7.0"
 
 [dependencies.arduino-hal]
 git = "https://github.com/rahix/avr-hal"

src/display.rs

@@ -82,169 +82,133 @@ impl SegmentPins {
 }
 
 #[derive(Clone, Copy, PartialEq, Eq)]
-pub struct Segment {
-    a: bool,
-    b: bool,
-    c: bool,
-    d: bool,
-    e: bool,
-    f: bool,
-    g: bool,
-    dp: bool,
-}
+pub struct Segment(u8);
 
 impl Segment {
     pub fn new() -> Segment {
-        Segment {
-            a: false,
-            b: false,
-            c: false,
-            d: false,
-            e: false,
-            f: false,
-            g: false,
-            dp: false,
-        }
+        Segment(0)
+    }
+
+    pub fn off(&mut self) -> &mut Self {
+        self.0 = 0;
+        self
+    }
+
+    pub fn a(&mut self) -> &mut Self {
+        self.0 |= 0b1000_0000;
+        self
+    }
+
+    pub fn b(&mut self) -> &mut Self {
+        self.0 |= 0b0100_0000;
+        self
+    }
+
+    pub fn c(&mut self) -> &mut Self {
+        self.0 |= 0b0010_0000;
+        self
+    }
+
+    pub fn d(&mut self) -> &mut Self {
+        self.0 |= 0b0001_0000;
+        self
+    }
+
+    pub fn e(&mut self) -> &mut Self {
+        self.0 |= 0b0000_1000;
+        self
+    }
+
+    pub fn f(&mut self) -> &mut Self {
+        self.0 |= 0b0000_0100;
+        self
+    }
+
+    pub fn g(&mut self) -> &mut Self {
+        self.0 |= 0b0000_0010;
+        self
+    }
+
+    pub fn dp(&mut self) -> &mut Self {
+        self.0 |= 0b0000_0001;
+        self
     }
 
     pub fn apply(&self, seg: &mut SegmentPins) {
         seg.set_off();
-        if self.a {
+        if self.0 & 0b1000_0000 != 0 {
             seg.set_a();
         }
-        if self.b {
+        if self.0 & 0b0100_0000 != 0 {
             seg.set_b();
         }
-        if self.c {
+        if self.0 & 0b0010_0000 != 0 {
             seg.set_c();
         }
-        if self.d {
+        if self.0 & 0b0001_0000 != 0 {
             seg.set_d();
         }
-        if self.e {
+        if self.0 & 0b0000_1000 != 0 {
             seg.set_e();
         }
-        if self.f {
+        if self.0 & 0b0000_0100 != 0 {
             seg.set_f();
         }
-        if self.g {
+        if self.0 & 0b0000_0010 != 0 {
             seg.set_g();
         }
-        if self.dp {
+        if self.0 & 0b0000_0001 != 0 {
             seg.set_dp();
         }
     }
 
-    pub fn off(&mut self) -> &mut Self {
-        self.a = false;
-        self.b = false;
-        self.c = false;
-        self.d = false;
-        self.e = false;
-        self.f = false;
-        self.g = false;
-        self.dp = false;
-        self
-    }
-
     pub fn num(&mut self, no: u8) -> &mut Self {
         match no {
             0 => {
-                self.a = true;
-                self.b = true;
-                self.c = true;
-                self.d = true;
-                self.e = true;
-                self.f = true;
+                self.a().b().c().d().e().f();
             }
             1 => {
-                self.b = true;
-                self.c = true;
+                self.b().c();
             }
             2 => {
-                self.a = true;
-                self.b = true;
-                self.g = true;
-                self.e = true;
-                self.d = true;
+                self.a().b().g().e().d();
             }
             3 => {
-                self.a = true;
-                self.b = true;
-                self.g = true;
-                self.c = true;
-                self.d = true;
+                self.a().b().g().c().d();
             }
             4 => {
-                self.f = true;
-                self.g = true;
-                self.b = true;
-                self.c = true;
+                self.f().g().b().c();
             }
             5 => {
-                self.a = true;
-                self.f = true;
-                self.g = true;
-                self.c = true;
-                self.d = true;
+                self.a().f().g().c().d();
             }
             6 => {
-                self.a = true;
-                self.f = true;
-                self.g = true;
-                self.c = true;
-                self.d = true;
-                self.e = true;
+                self.a().f().g().c().d().e();
             }
             7 => {
-                self.a = true;
-                self.b = true;
-                self.c = true;
+                self.a().b().c();
             }
             8 => {
-                self.a = true;
-                self.b = true;
-                self.c = true;
-                self.d = true;
-                self.e = true;
-                self.f = true;
-                self.g = true;
+                self.a().b().c().d().e().f().g();
             }
             9 => {
-                self.a = true;
-                self.b = true;
-                self.c = true;
-                self.d = true;
-                self.f = true;
-                self.g = true;
+                self.a().b().c().d().f().g();
             }
             _ => panic!("Num out of range"),
         }
         self
     }
 
-    pub fn dp(&mut self) -> &mut Self {
-        self.dp = true;
-        self
-    }
-
     pub fn minus(&mut self) -> &mut Self {
-        self.g = true;
-        self
+        self.g()
     }
 
     pub fn prompt(&mut self) -> &mut Self {
-        self.d = true;
-        self
+        self.d()
     }
 
-    pub fn e(&mut self) -> &mut Self {
-        self.a = true;
-        self.d = true;
-        self.e = true;
-        self.f = true;
-        self.g = true;
-        self
+    pub fn sym_e(&mut self) -> &mut Self {
+        self.a().d().e().f().g()
     }
 }
 
@@ -254,7 +218,7 @@ impl Default for Segment {
     }
 }
 
-#[derive(Default)]
+#[derive(Default, Clone, Copy)]
 pub struct DispalyState([Segment; DISPLAY_SEGMENTS]);
 
 impl Index<usize> for DispalyState {
@@ -272,6 +236,10 @@ impl IndexMut<usize> for DispalyState {
 }
 
 impl DispalyState {
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
     pub fn iter_segments(&self) -> impl Iterator<Item = &Segment> {
         self.0.iter()
     }
@@ -293,12 +261,16 @@ impl DispalyState {
         self[1].off();
         self[2].off();
         self[3].off().minus();
-        self[4].off().e();
+        self[4].off().sym_e();
         self[5].off().minus();
         self[6].off();
         self[7].off();
         self[8].off();
     }
+
+    pub fn slice(&mut self, start: usize, len: usize) -> &mut [Segment] {
+        &mut self.0.as_mut_slice()[start..(start + len)]
+    }
 }
 
 // Show data on segment display

src/io.rs

@@ -0,0 +1,52 @@
+use core::ops::{Index, IndexMut};
+
+use arduino_hal::{
+    hal::port::{PB3, PB4, PC1, PC2, PC3, PD2, PD3, PD4, PD7},
+    port::{mode::Output, Pin},
+};
+
+pub struct IOPins([Pin<Output>; 9]);
+
+impl IOPins {
+    pub fn new(
+        kd_d1_1c: Pin<Output, PD2>,
+        kd_d2_5div: Pin<Output, PD3>,
+        kd_d3_6mul: Pin<Output, PD4>,
+        kd_d4_7up: Pin<Output, PC3>,
+        kd_d5_8e: Pin<Output, PC2>,
+        kd_d6_90: Pin<Output, PD7>,
+        kd_d7_2down: Pin<Output, PC1>,
+        kd_d8_3plus: Pin<Output, PB3>,
+        kd_d9_4min: Pin<Output, PB4>,
+    ) -> IOPins {
+        IOPins([
+            kd_d1_1c.downgrade(),
+            kd_d2_5div.downgrade(),
+            kd_d3_6mul.downgrade(),
+            kd_d4_7up.downgrade(),
+            kd_d5_8e.downgrade(),
+            kd_d6_90.downgrade(),
+            kd_d7_2down.downgrade(),
+            kd_d8_3plus.downgrade(),
+            kd_d9_4min.downgrade(),
+        ])
+    }
+
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+}
+
+impl Index<usize> for IOPins {
+    type Output = Pin<Output>;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        &self.0[index]
+    }
+}
+
+impl IndexMut<usize> for IOPins {
+    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
+        &mut self.0[index]
+    }
+}

src/keyboard.rs

@@ -1,4 +1,7 @@
-use arduino_hal::{adc::AdcChannel, hal::Atmega, pac::ADC, Adc};
+use arduino_hal::{
+    adc::channel::{ADC6, ADC7},
+    Adc,
+};
 use ufmt::derive::uDebug;
 
 use crate::{DEBOUNCE_DEPTH, KEYBOARD_ADC_THRESHOLD};
@@ -49,13 +52,13 @@ pub struct KeyReadout {
     ko: bool,
 }
 
-pub struct Keyboard<KN, KO> {
-    kn: KN,
-    ko: KO,
+pub struct Keyboard {
+    kn: ADC7,
+    ko: ADC6,
 }
 
-impl<KN: AdcChannel<Atmega, ADC>, KO: AdcChannel<Atmega, ADC>> Keyboard<KN, KO> {
-    pub fn new(kn: KN, ko: KO) -> Keyboard<KN, KO> {
+impl Keyboard {
+    pub fn new(kn: ADC7, ko: ADC6) -> Keyboard {
         Keyboard { kn, ko }
     }
 
@@ -78,26 +81,24 @@ impl<KN: AdcChannel<Atmega, ADC>, KO: AdcChannel<Atmega, ADC>> Keyboard<KN, KO>
 pub struct Debounce {
     record: [Option<KeyReadout>; DEBOUNCE_DEPTH],
     pos: usize,
-    last: Option<KeyReadout>,
 }
 
 impl Debounce {
     pub fn input(&mut self, key: Option<KeyReadout>) -> Option<KeyPress> {
+        // React to fresh key press immediately if it was not pressed for depth of record
+        let new_key = key.and_then(|key| {
+            self.record
+                .iter()
+                .all(|hist| hist != &Some(key))
+                .then_some(key)
+        });
+
         self.record[self.pos] = key;
         self.pos += 1;
         if self.pos >= self.record.len() {
             self.pos = 0;
         }
-        if self.record.iter().all(|hist| hist == &key) && self.last != key {
-            self.last = key;
-            key.and_then(|key_readout| {
-                KeyPress::map(key_readout.display_no, key_readout.kn, key_readout.ko)
-            })
-        } else if self.record.iter().all(|hist| hist == &None) {
-            self.last = None;
-            None
-        } else {
-            None
-        }
+
+        new_key.and_then(|key| KeyPress::map(key.display_no, key.kn, key.ko))
     }
 }

src/main.rs

@@ -1,25 +1,35 @@
+#![feature(abi_avr_interrupt)]
 #![no_std]
 #![no_main]
 
 mod display;
+mod io;
 mod keyboard;
 mod panic;
+mod timer;
 
+use avr_device::{
+    asm::sleep,
+    interrupt::{CriticalSection, Mutex},
+};
 use calc_math::{
     calc::{StackCalc, StackCalcError},
     Decimal,
 };
+use core::cell::RefCell;
 use display::{DispalyState, SegmentPins, Show};
 use keyboard::{Debounce, KeyPress, KeyReadout, Keyboard};
 
 use arduino_hal::{
     adc::channel::{ADC6, ADC7},
-    hal::port::{PB3, PB4, PC1, PC2, PC3, PD2, PD3, PD4, PD7},
+    hal::port::PB5,
     port::{mode::Output, Pin},
     Adc,
 };
 use ufmt::derive::uDebug;
 
+use crate::io::IOPins;
+
 // NOTE: 115200 @ 16MHz is 3.5% off, try 9600 or 1M if it causes issues (https://wormfood.net/avrbaudcalc.php)
 const SERIAL_BAUD: u32 = 115200;
 // Analog threshold level of key press on ADC read from KN or KO
@@ -36,58 +46,134 @@ pub const DISPLAY_SEGMENT_SIG_MINUS: usize = 0;
 pub const DISPLAY_SEGMENTS_EXP: usize = 2;
 pub const DISPLAY_SEGMENT_EXP_MINUS: usize = 6;
 
-type Calc = StackCalc<f32, 3, 5, u8>;
+// Timing
+// Note: it takes ~224 μs to read keyboard after segment off
+pub const IO_SEGMENT_RATE_US: u32 = 1000; // Time in μs between segment updates
+pub const IO_SEGMENT_ON_US: u32 = 200; // How long in μs to hold segment LEDs on
 
-struct IOSelect<'p> {
-    display_no: usize,
-    pin: &'p mut Pin<Output>,
+// Calculator setup
+pub const STACK_DEPTH: usize = 7;
+type Calc = StackCalc<f32, STACK_DEPTH, 5, u8>;
+
+// Interrupt driven I/O
+//
+// * Run timer at 100Hz (10ms) to step through segments.
+// * On each segment interrupt configure segments and enable output (LEDs on).
+// * 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));
+
+fn try_access<'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
 }
 
-impl IOSelect<'_> {
-    fn display_no(&self) -> usize {
-        self.display_no
-    }
-
-    fn set_on(&mut self) {
-        self.pin.set_high()
-    }
-    fn set_off(&mut self) {
-        self.pin.set_low()
-    }
+#[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)");
+        try_access(&IO_LOOP, cs, |io_loop| {
+            io_loop.display_on();
+        })
+    });
 }
 
-struct IOPins([Pin<Output>; 9]);
+#[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| {
+            io_loop.display_off();
+            try_access(&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);
+                }
+            }
+        });
+    });
+}
 
-impl IOPins {
-    fn new(
-        kd_d1_1c: Pin<Output, PD2>,
-        kd_d2_5div: Pin<Output, PD3>,
-        kd_d3_6mul: Pin<Output, PD4>,
-        kd_d4_7up: Pin<Output, PC3>,
-        kd_d5_8e: Pin<Output, PC2>,
-        kd_d6_90: Pin<Output, PD7>,
-        kd_d7_2down: Pin<Output, PC1>,
-        kd_d8_3plus: Pin<Output, PB3>,
-        kd_d9_4min: Pin<Output, PB4>,
-    ) -> IOPins {
-        IOPins([
-            kd_d1_1c.downgrade(),
-            kd_d2_5div.downgrade(),
-            kd_d3_6mul.downgrade(),
-            kd_d4_7up.downgrade(),
-            kd_d5_8e.downgrade(),
-            kd_d6_90.downgrade(),
-            kd_d7_2down.downgrade(),
-            kd_d8_3plus.downgrade(),
-            kd_d9_4min.downgrade(),
-        ])
+pub struct IOLoop {
+    index: usize,
+    io_pins: IOPins,
+    segment_pins: SegmentPins,
+    dispaly: DispalyState,
+    keyboard: Keyboard,
+    readount: Option<KeyReadout>,
+    debounce: Debounce,
+}
+
+impl IOLoop {
+    pub fn new(io_pins: IOPins, segment_pins: SegmentPins, keyboard: Keyboard) -> IOLoop {
+        IOLoop {
+            index: 0,
+            io_pins,
+            segment_pins,
+            dispaly: Default::default(),
+            keyboard,
+            readount: None,
+            debounce: Default::default(),
+        }
     }
 
-    fn iter_mut(&mut self) -> impl Iterator<Item = IOSelect> {
-        self.0
-            .iter_mut()
-            .enumerate()
-            .map(|(display_no, pin)| IOSelect { display_no, pin })
+    pub fn update_display(&mut self, display: &DispalyState) {
+        self.dispaly = *display;
+    }
+
+    fn select_on(&mut self) {
+        self.io_pins[self.index].set_high();
+    }
+
+    fn select_off(&mut self) {
+        self.io_pins[self.index].set_low();
+    }
+
+    pub fn advance(&mut self) -> Option<KeyPress> {
+        self.index += 1;
+        if self.index == self.io_pins.len() || self.index == self.dispaly.len() {
+            // Start from first segment
+            self.index = 0;
+
+            // Full keyboard scan complete, debounce and return result
+            self.debounce.input(self.readount.take())
+        } else {
+            None
+        }
+    }
+
+    pub fn display_on(&mut self) {
+        self.select_off();
+        let segment = self.dispaly[self.index];
+        segment.apply(&mut self.segment_pins);
+        self.select_on();
+    }
+
+    pub fn display_off(&mut self) {
+        self.select_off();
+        self.segment_pins.set_off();
+    }
+
+    pub fn read_key(&mut self, adc: &mut Adc) {
+        self.select_on();
+        if let key_readout @ Some(_) = self.keyboard.read(adc, self.index) {
+            self.readount = key_readout;
+        }
+        self.select_off();
     }
 }
 
@@ -192,22 +278,47 @@ impl Show for NumberInput {
     fn show(&self, display: &mut DispalyState) {
         display.off();
         display[1].dp();
-        if !self.enter_exponent && self.significant_pos < DISPLAY_SEGMENTS_SIG {
-            display[self.significant_pos + 1].prompt();
-        } else if self.enter_exponent && self.exponent_pos < DISPLAY_SEGMENTS_EXP {
-            display[DISPLAY_SEGMENTS_SIG + 2 + self.exponent_pos].prompt();
-        }
+
+        let (minus, sig) = display.slice(0, 1 + DISPLAY_SEGMENTS_SIG).split_at_mut(1);
+
         if self.minus {
-            display[DISPLAY_SEGMENT_SIG_MINUS].minus();
+            minus[0].minus();
         }
-        for i in 0..self.significant_pos {
-            display[DISPLAY_SEGMENT_SIG_MINUS + 1 + i].num(self.significant[i]);
+
+        for (seg, num) in sig
+            .iter_mut()
+            .zip(self.significant.iter())
+            .take(self.significant_pos)
+        {
+            seg.num(*num);
         }
+
+        if !self.enter_exponent {
+            if let Some(seg) = sig.get_mut(self.significant_pos) {
+                seg.prompt();
+            }
+        }
+
+        let (minus, exp) = display
+            .slice(1 + DISPLAY_SEGMENTS_SIG, 1 + DISPLAY_SEGMENTS_EXP)
+            .split_at_mut(1);
+
         if self.minus_exponent {
-            display[DISPLAY_SEGMENT_EXP_MINUS].minus();
+            minus[0].minus();
         }
-        for i in 0..self.exponent_pos {
-            display[DISPLAY_SEGMENT_EXP_MINUS + 1 + i].num(self.exponent[i]);
+
+        for (seg, num) in exp
+            .iter_mut()
+            .zip(self.exponent.iter())
+            .take(self.exponent_pos)
+        {
+            seg.num(*num);
+        }
+
+        if self.enter_exponent {
+            if let Some(seg) = exp.get_mut(self.exponent_pos) {
+                seg.prompt();
+            }
         }
     }
 }
@@ -378,7 +489,7 @@ fn main() -> ! {
 
     ufmt::uwriteln!(&mut serial, "Hello from Arduino!").ok();
 
-    let mut io = IOPins::new(
+    let io_pins = IOPins::new(
         pins.d2.into_output(),
         pins.d3.into_output(),
         pins.d4.into_output(),
@@ -389,8 +500,7 @@ fn main() -> ! {
         pins.d11.into_output(),
         pins.d12.into_output(),
     );
-
-    let mut seg = SegmentPins::new(
+    let segment_pins = SegmentPins::new(
         pins.d5.into_output(),
         pins.d8.into_output(),
         pins.d10.into_output(),
@@ -400,10 +510,11 @@ fn main() -> ! {
         pins.a0.into_output(),
         pins.a4.into_output(),
     );
-
-    let mut adc = Adc::new(dp.ADC, Default::default());
     let keyboard = Keyboard::new(ADC7, ADC6);
-    let mut debounce = Debounce::default();
+    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 mut number_input = NumberInput::default();
 
     let mut display = DispalyState::default();
@@ -415,24 +526,28 @@ fn main() -> ! {
         calculator: CalcluclatorState::EnterSignificant,
     };
 
-    loop {
-        let mut last_key_readout: Option<KeyReadout> = None;
-        for (mut io_select, ss) in io.iter_mut().zip(display.iter_segments()) {
-            ss.apply(&mut seg);
-            io_select.set_on();
-            arduino_hal::delay_ms(1);
-            io_select.set_off();
-            seg.set_off();
-            io_select.set_on();
-            if let key_readout @ Some(_) = keyboard.read(&mut adc, io_select.display_no()) {
-                last_key_readout = key_readout;
-            }
-            io_select.set_off();
-        }
+    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));
+    });
+    timer::segment_timer_init(
+        dp.TC0, // Timer0 (8bit)
+        IO_SEGMENT_RATE_US,
+        IO_SEGMENT_ON_US,
+    );
+    unsafe {
+        avr_device::interrupt::enable();
+    }
 
-        let key = debounce.input(last_key_readout);
+    loop {
+        let mut key = None;
+        avr_device::interrupt::free(|cs| {
+            key = KEY_PRESS.borrow(cs).borrow_mut().take();
+        });
 
         if let TransientState::Done = state.transient {
+            // No transient state - handle key or wait for key
             if let Some(key) = key {
                 ufmt::uwriteln!(
                     &mut serial,
@@ -467,16 +582,35 @@ fn main() -> ! {
                 for (i, dec) in calc.iter().enumerate() {
                     ufmt::uwriteln!(&mut serial, "[{}] {}", i, dec).ok();
                 }
+            } else {
+                // Wait for key
+                sleep(); // Enter idle mode; wake up on interrupt
             }
         } else {
-            state.transient.on_frame(key)
+            // In transient state - handle animation
+            arduino_hal::delay_ms(10);
+            state.transient.on_frame(key);
         }
 
         match &state.transient {
-            TransientState::Done => number_input.show(&mut display),
+            TransientState::Done => {
+                number_input.show(&mut display);
+                for seg in display
+                    .slice(0, DISPLAY_SEGMENTS)
+                    .iter_mut()
+                    .rev()
+                    .take(calc.len())
+                {
+                    seg.dp();
+                }
+            }
             TransientState::Err { .. } => display.error(),
         }
 
-        arduino_hal::delay_ms(1);
+        avr_device::interrupt::free(|cs| {
+            try_access(&IO_LOOP, cs, |io_loop| {
+                io_loop.update_display(&display);
+            });
+        });
     }
 }

src/timer.rs

@@ -0,0 +1,26 @@
+use arduino_hal::{clock::Clock, pac::TC0, DefaultClock};
+
+// Sets up timer to rise two interrupts:
+// 1. TIMER0_COMPA - every segment_rate_us μs
+// 2. TIMER0_COMPB - segment_on_us μs after TIMER0_COMPA
+pub fn segment_timer_init(tc0: TC0, segment_rate_us: u32, segment_on_us: u32) {
+    // 16_000_000 / 64 * 1000 / 1_000_000 => 250
+    let ocra = DefaultClock::FREQ / 64 * segment_rate_us / 1_000_000;
+    let ocrb = DefaultClock::FREQ / 64 * segment_on_us / 1_000_000;
+    assert!(ocra > ocrb);
+
+    // Use CTC mode: reset counter when matches compare value
+    tc0.tccr0a.write(|w| w.wgm0().ctc());
+    // Set the compare value for TOP (reset)
+    tc0.ocr0a
+        .write(|w| w.bits(ocra.try_into().expect("timer init seg_freq out of rage")));
+    // Set the compare value for B match
+    tc0.ocr0b
+        .write(|w| w.bits(ocrb.try_into().expect("timer init on_div out of rage")));
+    // Slow down the timer (CLK / prescale)
+    tc0.tccr0b.write(|w| w.cs0().prescale_64());
+    // Raise interrupt on TOP (reset)
+    // Raise interrupt on B match
+    tc0.timsk0
+        .write(|w| w.ocie0a().set_bit().ocie0b().set_bit());
+}