Merge pull request #127 from mattheww/2024-01_mb2-refresh

Double the non-blocking display refresh frequency for the micro:bit V2

Author: lulf

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+- Double the non-blocking display refresh frequency for the micro:bit V2
 - Fix faulty doc test in `blocking.rs`
 - Update the non-blocking display documentation to better explain when methods
   should be called from within a critical section

microbit-common/src/display/nonblocking/mod.rs

@@ -117,17 +117,21 @@
 //! The [`Display`] expects to control a single timer. It can use the
 //! micro:bit's `TIMER0`, `TIMER1`, or `TIMER2`.
 //!
-//! This uses a 6ms period to light each of the three internal LED rows, so
-//! that the entire display is updated every 18ms.
+//! For the micro:bit v1 this uses a 6ms period to light each of the three
+//! internal LED rows, so that the entire display is updated every 18ms.
+//!
+//! For the micro:bit v2 this uses a 3ms period to light each of the five
+//! internal LED rows, so that the entire display is updated every 15ms.
 //!
 //! When rendering greyscale images, the `Display` requests extra interrupts
-//! within each 6ms period. It only requests interrupts for the greyscale
-//! levels which are actually required for what's currently being displayed.
+//! within each 6ms or 3ms period. It only requests interrupts for the
+//! greyscale levels which are actually required for what's currently being
+//! displayed.
 //!
 //! ### Technical details
 //!
-//! The timer is set to 16-bit mode, using a 62.5kHz clock (16 µs ticks). It
-//! resets every 375 ticks.
+//! The timer is set to 16-bit mode, using a 62.5kHz or 135Khz clock (16 µs or
+//! 8µs ticks). It resets every 375 ticks.
 //!
 //! ## Usage
 //!
@@ -137,7 +141,7 @@
 //! - create a [`Display`] struct passing the timer and
 //! [`gpio::DisplayPins`](crate::gpio::DisplayPins) to [`Display::new()`].
 //!
-//! In an interrupt handler forthe timer call [`.handle_display_event()`](Display::handle_display_event)
+//! In an interrupt handler for the timer call [`.handle_display_event()`](Display::handle_display_event)
 //!
 //! To change what's displayed; pass an image ([`GreyscaleImage`] or [`BitImage`]) to [`Display::show`].
 //!

microbit-common/src/display/nonblocking/timer.rs

@@ -10,9 +10,14 @@ use crate::hal::timer::Instance;
 ///
 /// `MicrobitDisplayTimer` instances implement the [`DisplayTimer`] trait.
 ///
-/// The timer is set to 16-bit mode, using a 62.5kHz clock (16 µs ticks).
+/// The timer is set to 16-bit mode.
+///
+/// For micro:bit v1: uses a 62.5kHz clock clock (16 µs ticks).
 /// The primary cycle takes 6ms.
 ///
+/// For micro:bit v2: uses a 135kHz clock (8 µs ticks).
+/// The primary cycle takes 3ms.
+///
 /// Uses CC0 for the primary cycle and CC1 for the secondary alarm. Uses the
 /// CC0_CLEAR shortcut to implement the primary cycle.
 ///
@@ -43,8 +48,13 @@ impl<T: Instance> DisplayTimer for MicrobitDisplayTimer<T> {
         // set as 16 bits
         timer0.bitmode.write(|w| w.bitmode()._16bit());
 
+        #[cfg(feature = "v1")]
         // set frequency to 62500Hz
-        timer0.prescaler.write(|w| unsafe { w.bits(8) });
+        let prescaler = 8;
+        #[cfg(feature = "v2")]
+        // set frequency to 135000Hz
+        let prescaler = 7;
+        timer0.prescaler.write(|w| unsafe { w.bits(prescaler) });
 
         // set compare register
         timer0.cc[0].write(|w| unsafe { w.bits(ticks.into()) });