timer refactoring

src/timer.rs

@@ -1,22 +1,46 @@
 use arduino_hal::{clock::Clock, pac::TC0, DefaultClock};
 
+// 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;
+
+// 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
+}
+
 // 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) {
+// 1. TIMER0_COMPA - segment_switch_us - time in μs to switch to next segment
+// 2. TIMER0_COMPB - segment_on_us - time in μs to keep segment LEDs on
+pub fn segment_timer_init(tc0: TC0, segment_switch_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);
+    let ocra = us_to_ticks(segment_switch_us);
+    let ocrb = us_to_ticks(segment_on_us);
+    assert!(
+        ocra > ocrb + BUFFER_TICKS,
+        "segment_on_us cannot be longer than segment_switch_us - buffer"
+    );
 
     // 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")));
+    tc0.ocr0a.write(|w| {
+        w.bits(
+            ocra.try_into()
+                .expect("timer init segment_switch_us 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.ocr0b.write(|w| {
+        w.bits(
+            ocrb.try_into()
+                .expect("timer init segment_on_us out of rage"),
+        )
+    });
     // Slow down the timer (CLK / prescale)
     tc0.tccr0b.write(|w| w.cs0().prescale_64());
     // Raise interrupt on TOP (reset)
@@ -24,3 +48,20 @@ pub fn segment_timer_init(tc0: TC0, segment_rate_us: u32, segment_on_us: u32) {
     tc0.timsk0
         .write(|w| w.ocie0a().set_bit().ocie0b().set_bit());
 }
+
+// Set for how long the segment LEDs should be on in μs
+pub fn set_segment_on_time(tc0: TC0, segment_on_us: u32) {
+    let ocra = tc0.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
+    tc0.ocr0b.write(|w| {
+        w.bits(
+            ocrb.try_into()
+                .expect("timer init segment_on_us out of rage"),
+        )
+    });
+}