Low Power#

RMK supports low-power mode by utilizing embassy's low-power feature and the Wait trait in embedded-hal-async.

Usage#

By default, RMK uses a busy-loop for matrix scanning, which is not very power efficient. To enable the low-power mode, add the async_matrix feature to your Cargo.toml:

1rmk = { version = "...", features = [
2    "nrf52840_ble",
3    "async_matrix",
4] }

If you're using nRF chips or RP2040, you're all set! Your keyboard is now running in low-power mode. The async_matrix feature enables interrupt-based input detection, and puts your microcontroller into sleep mode when no keys are being pressed.

For STM32, there are some limitations about EXTI (see here):

EXTI is not built into Input itself because it needs to take ownership of the corresponding EXTI channel, which is a limited resource.

Pins PA5, PB5, PC5… all use EXTI channel 5, so you can’t use EXTI on, say, PA5 and PC5 at the same time.

There are a few more things that you need to do:

1. Enable the exti feature for your embassy-stm32 dependency in Cargo.toml
2. Ensure that your input pins don't share the same EXTI channel
3. For configuration:
   • If you're using keyboard.toml, you are all set. The [rmk_keyboard] macro will automatically check your Cargo.toml and handle it for you.
   • If you're using Rust code, you'll need to use ExtiInput for your input pins:

let pd9 = ExtiInput::new(p.PD9,  p.EXTI9, Pull::Down);
    let pd8 = ExtiInput::new(p.PD8,  p.EXTI8, Pull::Down);
    let pb13 = ExtiInput::new(p.PB13, p.EXTI13, Pull::Down);
    let pb12 = ExtiInput::new(p.PB12, p.EXTI12, Pull::Down);
    let row_pins = [pd9, pd8, pb13, pb12];

    let mut matrix = Matrix::<_, _, _, ROW, COL, true>::new(row_pins, col_pins, debouncer);

External VCC#

Some boards, such as the nice!nano have an external 3.3V regulator that can be used to power the LEDs. If not used, the regulator can be disabled by pulling P0_13 low to safe power.

In the case of the nice!nano, this can be done by adding the following line to main.rs

// Disable external voltage regulator
    Output::new(peripherals.P0_13, Level::Low, OutputDrive::Standard).persist();

or the following snippet to your keyboard.toml:

[[output]]
pin = "P0_13"
initial_state_active = false