Module etm

Available on crate feature unstable only.

Event Task Matrix (ETM)

Overview

Normally, if a peripheral X needs to notify peripheral Y of a particular event, this could only be done via a CPU interrupt from peripheral X, where the CPU notifies peripheral Y on behalf of peripheral X. However, in time-critical applications, the latency introduced by CPU interrupts is non-negligible.

With the help of the Event Task Matrix (ETM) module, some peripherals can directly notify other peripherals of events through pre-set connections without the intervention of CPU interrupts. This allows precise and low latency synchronization between peripherals, and lessens the CPU’s workload as the CPU no longer needs to handle these events.

The ETM module has multiple programmable channels, they are used to connect a particular Event to a particular Task. When an event is activated, the ETM channel will trigger the corresponding task automatically.

For more information, please refer to the ESP-IDF documentation

Examples

Control LED by the button via ETM

let mut led = peripherals.GPIO1;
let button = peripherals.GPIO9;

// setup ETM
let gpio_ext = Channels::new(peripherals.GPIO_SD);
let led_task = gpio_ext.channel0_task.toggle(
    &mut led,
    OutputConfig {
        open_drain: false,
        pull: Pull::None,
        initial_state: Level::Low,
    },
);
let button_event = gpio_ext
.channel0_event
.falling_edge(button, InputConfig { pull: Pull::Down });

let etm = Etm::new(peripherals.SOC_ETM);
let channel0 = etm.channel0;

// make sure the configured channel doesn't get dropped - dropping it will
// disable the channel
let _configured_channel = channel0.setup(&button_event, &led_task);

// the LED is controlled by the button without involving the CPU
loop {}

Control LED by the systimer via ETM

use esp_hal::time::Duration;

let syst = SystemTimer::new(peripherals.SYSTIMER);
let mut alarm0 = syst.alarm0;
let mut timer = PeriodicTimer::new(&mut alarm0);
timer.start(Duration::from_secs(1));

let mut led = peripherals.GPIO1;

// setup ETM
let gpio_ext = Channels::new(peripherals.GPIO_SD);
let led_task = gpio_ext.channel0_task.toggle(
    &mut led,
    OutputConfig {
        open_drain: false,
        pull: Pull::None,
        initial_state: Level::Low,
    },
);

let timer_event = Event::new(&mut alarm0);

let etm = Etm::new(peripherals.SOC_ETM);
let channel0 = etm.channel0;

// make sure the configured channel doesn't get dropped - dropping it will
// disable the channel
let _configured_channel = channel0.setup(&timer_event, &led_task);

// the LED is controlled by the timer without involving the CPU
loop {}

Structs

Etm

ETM Instance

EtmChannel

Unconfigured EtmChannel.

EtmConfiguredChannel

A readily configured channel