From 1f961964f0e67c26ffc2ce28846bee77f39f6bed Mon Sep 17 00:00:00 2001
From: Hexa Dust <hxd@hexadust.net>
Date: Fri, 18 Jul 2025 20:31:23 +0100
Subject: [PATCH] use B compare match register to trigger interrupt

---
 src/main.rs  | 31 +++++++++++++++++++++++--------
 src/timer.rs | 24 ++++++++++++++++++------
 2 files changed, 41 insertions(+), 14 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 94b4770..d3154a1 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -18,10 +18,9 @@ use keyboard::{Debounce, KeyPress, KeyReadout, Keyboard};
 
 use arduino_hal::{
     adc::channel::{ADC6, ADC7},
-    clock::Clock,
     hal::port::{PB3, PB4, PB5, PC1, PC2, PC3, PD2, PD3, PD4, PD7},
     port::{mode::Output, Pin},
-    Adc, DefaultClock,
+    Adc,
 };
 use ufmt::derive::uDebug;
 
@@ -41,6 +40,10 @@ pub const DISPLAY_SEGMENT_SIG_MINUS: usize = 0;
 pub const DISPLAY_SEGMENTS_EXP: usize = 2;
 pub const DISPLAY_SEGMENT_EXP_MINUS: usize = 6;
 
+// Timing
+pub const IO_SEG_REFRESH_FREQ: u32 = 100; // Segment timer freq; from 62 to 15779 for 8bit counter
+pub const IO_SEG_ON_DIV: u32 = 10; // How long to hold segment LEDs on as part of time for segment timer
+
 pub const STACK_DEPTH: usize = 7;
 
 type Calc = StackCalc<f32, STACK_DEPTH, 5, u8>;
@@ -61,11 +64,22 @@ unsafe fn TIMER0_COMPA() {
     // ...
     avr_device::interrupt::free(
         |cs| match LED.borrow(cs).borrow_mut().deref_mut().as_mut() {
-            Some(led) => led.toggle(),
+            // Some(led) => led.toggle(),
+            Some(led) => led.set_high(),
+            None => panic!(),
+        },
+    );
+}
+
+#[avr_device::interrupt(atmega328p)]
+unsafe fn TIMER0_COMPB() {
+    //TODO: Disable display segment and handle keyboard input for current segment
+    avr_device::interrupt::free(
+        |cs| match LED.borrow(cs).borrow_mut().deref_mut().as_mut() {
+            Some(led) => led.set_low(),
             None => panic!(),
         },
     );
-    //..toggle());
 }
 
 struct IOSelect<'p> {
@@ -470,13 +484,14 @@ fn main() -> ! {
         calculator: CalcluclatorState::EnterSignificant,
     };
 
-    // TODO: configure timer, enable it to interrupt: dp.TC1.tifr1
-    // https://github.com/monoper/rust-atmega328p/blob/main/arduino-nano/key-tmr-input/src/main.rs
-    timer::segment_timer_init(dp.TC0, (DefaultClock::FREQ / 1024 / 100) as u8); // 16_000_000 / 1024 / 100 => 156
     avr_device::interrupt::free(|cs| {
         LED.borrow(cs).replace(Some(pins.d13.into_output()));
     });
-
+    timer::segment_timer_init(
+        dp.TC0,              // Timer0 (8bit)
+        IO_SEG_REFRESH_FREQ, // run segments at 100Hz
+        IO_SEG_ON_DIV,       // 1/10th of 100Hz, 1ms segment on time
+    );
     unsafe {
         avr_device::interrupt::enable();
     }
diff --git a/src/timer.rs b/src/timer.rs
index 5dd76b6..9e307f0 100644
--- a/src/timer.rs
+++ b/src/timer.rs
@@ -1,12 +1,24 @@
-use arduino_hal::pac::TC0;
+use arduino_hal::{clock::Clock, pac::TC0, DefaultClock};
+
+// Raises two interrupts: TIMER0_COMPA every period cycles/1024
+// and TIMER0_COMPB compb_cocunt cycles/1024 after TIMER0_COMPA
+pub fn segment_timer_init(tc0: TC0, seg_freq: u32, on_div: u32) {
+    // 16_000_000 / 1024 / 100 => 156 (100Hz|10ms)
+    let ocra = DefaultClock::FREQ / 1024 / seg_freq;
+    let ocrb: u32 = ocra / on_div;
 
-pub fn segment_timer_init(tc0: TC0, counts: u8) {
     // Use CTC mode: reset counter when matches compare value
     tc0.tccr0a.write(|w| w.wgm0().ctc());
-    // Set the compare value
-    tc0.ocr0a.write(|w| w.bits(counts));
+    // 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_1024());
-    // Raise interrupt on reset
-    tc0.timsk0.write(|w| w.ocie0a().set_bit());
+    // Raise interrupt on counter TOP (reset)
+    // Raise interrupt on B match
+    tc0.timsk0
+        .write(|w| w.ocie0a().set_bit().ocie0b().set_bit());
 }