linear dimming

src/display.rs

@@ -5,7 +5,7 @@ use arduino_hal::{
     port::{mode::Output, Pin},
 };
 
-use crate::DISPLAY_SEGMENTS;
+use crate::{DISPLAY_SEGMENTS, IO_SEGMENT_ON_MAX_US, IO_SEGMENT_ON_MIN_US};
 
 pub struct SegmentPins {
     kd_seg_a: Pin<Output, PD5>,
@@ -82,11 +82,43 @@ impl SegmentPins {
 }
 
 #[derive(Clone, Copy, PartialEq, Eq)]
-pub struct Segment(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
+    }
+
+    pub fn dimm(self, dimming: u8) -> Brightness {
+        Brightness(self.0.saturating_sub(dimming))
+    }
+
+    // Scales brightness (0-255) to range between IO_SEGMENT_ON_MIN_US and IO_SEGMENT_ON_MAX_US
+    pub fn scale_brightness(self) -> u32 {
+        // Using >> to avoid 32bit division which take ~576 cycles
+        IO_SEGMENT_ON_MIN_US + ((IO_SEGMENT_ON_MAX_US - IO_SEGMENT_ON_MIN_US) * self.0 as u32 >> 8)
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub struct Segment(u8, Brightness);
 
 impl Segment {
     pub fn new() -> Segment {
-        Segment(0)
+        Segment(0, Brightness::full())
+    }
+
+    pub fn brightness(&mut self, b: Brightness) -> &mut Self {
+        self.1 = b;
+        self
     }
 
     pub fn off(&mut self) -> &mut Self {
@@ -134,7 +166,7 @@ impl Segment {
         self
     }
 
-    pub fn apply(&self, seg: &mut SegmentPins) {
+    pub fn apply(&self, seg: &mut SegmentPins) -> Brightness {
         seg.set_off();
         if self.0 & 0b1000_0000 != 0 {
             seg.set_a();
@@ -160,6 +192,7 @@ impl Segment {
         if self.0 & 0b0000_0001 != 0 {
             seg.set_dp();
         }
+        self.1
     }
 
     pub fn num(&mut self, no: u8) -> &mut Self {

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,
@@ -22,13 +22,11 @@ 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;
 
-use crate::io::IOPins;
+use crate::{display::Brightness, io::IOPins, timer::SegmentTimer};
 
 // 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;
@@ -49,7 +47,14 @@ pub const DISPLAY_SEGMENT_EXP_MINUS: usize = 6;
 // 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
+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)
+
+// Dimming
+pub const DISPLAY_FPS: u16 = (1_000_000 / (IO_SEGMENT_RATE_US * DISPLAY_SEGMENTS as u32)) as u16;
+pub const DISPLAY_DIMM_FRAMES: u16 = DISPLAY_FPS * 10; // How many frames of inactivity before dimming
+pub const DISPLAY_DIMM_SPEED: u8 = 4; // Dimm by amount every frame when sleeping
+pub const DISPLAY_UNDIMM_SPEED: u8 = 16; // Brighten by amount every frame when not sleeping
 
 // Calculator setup
 pub const STACK_DEPTH: usize = 7;
@@ -62,47 +67,46 @@ 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));
+// 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)");
-        try_access(&IO_LOOP, cs, |io_loop| {
-            io_loop.display_on();
-        })
+        access_global(&IO_LOOP, cs, |io_loop| {
+            access_global(&SEGMENT_TIMER, cs, |st| {
+                let brightness = io_loop.display_on();
+                st.segment_on_time(brightness.scale_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));
             }
         });
     });
@@ -110,24 +114,30 @@ unsafe fn TIMER0_COMPB() {
 
 pub struct IOLoop {
     index: usize,
+    frame: u16,
     io_pins: IOPins,
     segment_pins: SegmentPins,
     dispaly: DispalyState,
     keyboard: Keyboard,
     readount: Option<KeyReadout>,
     debounce: Debounce,
+    sleep_timer: u16,
+    dimming: u8,
 }
 
 impl IOLoop {
     pub fn new(io_pins: IOPins, segment_pins: SegmentPins, keyboard: Keyboard) -> IOLoop {
         IOLoop {
             index: 0,
+            frame: 0,
             io_pins,
             segment_pins,
             dispaly: Default::default(),
             keyboard,
             readount: None,
             debounce: Default::default(),
+            sleep_timer: 0,
+            dimming: u8::MAX,
         }
     }
 
@@ -146,21 +156,47 @@ impl IOLoop {
     pub fn advance(&mut self) -> Option<KeyPress> {
         self.index += 1;
         if self.index == self.io_pins.len() || self.index == self.dispaly.len() {
+            // Frame done
+            self.frame = self.frame.wrapping_add(1);
             // Start from first segment
             self.index = 0;
 
-            // Full keyboard scan complete, debounce and return result
-            self.debounce.input(self.readount.take())
+            // Full keyboard scan complete, debounce
+            let key = self.debounce.input(self.readount.take());
+
+            // Reset or advance sleep timer
+            if key.is_some() {
+                self.sleep_timer = 0;
+            } else {
+                self.sleep_timer = self.sleep_timer.saturating_add(1);
+            }
+
+            if self.is_sleep() {
+                self.dimming = self.dimming.saturating_add(DISPLAY_DIMM_SPEED);
+            } else {
+                self.dimming = self.dimming.saturating_sub(DISPLAY_UNDIMM_SPEED);
+            }
+
+            key
         } else {
             None
         }
     }
 
-    pub fn display_on(&mut self) {
+    pub fn is_sleep(&self) -> bool {
+        self.sleep_timer >= DISPLAY_DIMM_FRAMES
+    }
+
+    pub fn dimming(&self) -> u8 {
+        self.dimming
+    }
+
+    pub fn display_on(&mut self) -> Brightness {
         self.select_off();
         let segment = self.dispaly[self.index];
-        segment.apply(&mut self.segment_pins);
+        let brighness = segment.apply(&mut self.segment_pins);
         self.select_on();
+        brighness.dimm(self.dimming)
     }
 
     pub fn display_off(&mut self) {
@@ -175,6 +211,10 @@ impl IOLoop {
         }
         self.select_off();
     }
+
+    pub fn frame(&self) -> (u16, usize) {
+        (self.frame, self.index)
+    }
 }
 
 #[derive(uDebug)]
@@ -512,8 +552,8 @@ 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);
 
     let mut number_input = NumberInput::default();
 
@@ -527,15 +567,10 @@ 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));
     });
-    timer::segment_timer_init(
-        dp.TC0, // Timer0 (8bit)
-        IO_SEGMENT_RATE_US,
-        IO_SEGMENT_ON_US,
-    );
     unsafe {
         avr_device::interrupt::enable();
     }
@@ -543,7 +578,7 @@ 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 {
@@ -602,15 +637,16 @@ fn main() -> ! {
                     .take(calc.len())
                 {
                     seg.dp();
+                    seg.brightness(Brightness::full());
                 }
             }
             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);
-            });
+            })
         });
     }
 }

src/timer.rs

@@ -1,26 +1,54 @@
 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) {
+// Prescaler set for the timer (see tccr0b)
+const TIMER_PRESCALE: u32 = 64;
+// Timer clock tick rate per second
+const TIMER_FREQ: u32 = DefaultClock::FREQ / TIMER_PRESCALE;
+
+const fn us_to_ticks(us: u32) -> u32 {
+    TIMER_FREQ * us / 1_000_000
+}
+
+// Timer 0 (8bit)
+pub struct SegmentTimer {
+    timer: TC0,
+}
+
+impl SegmentTimer {
+    // Sets up timer to rise interrupts:
+    // 1. TIMER0_COMPA - segment_switch_us - time in μs to switch to next segment
+    // 2. TIMER0_COMPB - set by set_segment_on_time to keep segment LEDs on
+    pub fn init(tc0: TC0, segment_switch_us: u32) -> SegmentTimer {
         // 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);
+        let ocra = us_to_ticks(segment_switch_us);
 
         // 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")));
+        tc0.ocr0a.write(|w| {
+            w.bits(
+                ocra.try_into()
+                    .expect("timer init segment_switch_us 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());
+
+        SegmentTimer { timer: tc0 }
+    }
+
+    // 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 delay: u8 = us_to_ticks(segment_on_us)
+            .try_into()
+            .expect("timer init segment_on_us out of rage");
+        let elapsed = self.timer.tcnt0.read().bits();
+        // Set the compare value for B match
+        self.timer.ocr0b.write(|w| w.bits(elapsed + delay));
+    }
 }