Trait DisplayTimer

pub trait DisplayTimer {
    // Required methods
    fn initialise_cycle(&mut self, ticks: u16);
    fn enable_secondary(&mut self);
    fn disable_secondary(&mut self);
    fn program_secondary(&mut self, ticks: u16);
    fn check_primary(&mut self) -> bool;
    fn check_secondary(&mut self) -> bool;
}

The interface that Display needs to work with a timer.

The timer should count ticks of a fixed size.

It should reset itself after the number of ticks passed to initialise_cycle() have elapsed (the primary cycle), and signal an interrupt.

It should also provide a secondary alarm which can be programmed to signal an interrupt at a specified point during the primary cycle.

If you provide a ‘no-op’ implementation of the secondary-alarm features, the effect will be a display which treats brightness level 9 as on and all other levels as off.

Choosing the tick length

The cycle length is in fact always 375 ticks, so the display will be fully refreshed after MATRIX_ROWS×375 ticks. Aiming for around 60 refreshes per second is common.

For example, if there are three matrix rows you might use a tick period of 16µs. Then the display will be refreshed every 18ms, or about 55 times a second (this is the refresh rate used for the micro:bit runtime and the micro:bit MicroPython port).

Required Methods

fn initialise_cycle(&mut self, ticks: u16)

Initialises the timer.

This is intended to be called once, before using the display.

The ticks parameter is the number of ticks in the primary cycle.

Leaves the secondary alarm disabled.

fn enable_secondary(&mut self)

Enables the secondary alarm.

After this is called, an interrupt should be generated each time the tick last passed to program_secondary()is reached.

fn disable_secondary(&mut self)

Disables the secondary alarm.

After this is called, no more interrupts should be generated from the secondary alarm until it is enabled again.

fn program_secondary(&mut self, ticks: u16)

Specifies the tick to use for the secondary alarm.

Note that ticks represents the time after the start of the primary cycle (not the time after the previous secondary signal).

fn check_primary(&mut self) -> bool

Checks whether a new primary cycle has begun since the last call to this method.

fn check_secondary(&mut self) -> bool

Checks whether the secondary alarm has signalled an interrupt since the last call to this method.

Implementors