ESP32-S开发之 FreeRTOS Notification

发表于 2022-01-11 更新于 2022-12-11 分类于 28IoT 阅读次数：

本文基于ESP32-S开发之 FreeRTOS Task

本文的主线信号 => 简介 => 通知 => 问题

信号

python
>>> import os
>>> print(os.getpid())
81062

1	kill -3 81062

1 2	man kill kill - send a signal to a process

Linux Kernel

简介

A direct to task notification is an event sent directly to a task, rather than indirectly to a task via an intermediary object such as a queue, event group or semaphore. Sending a direct to task notification to a task sets the state of the target task notification to ‘pending’. Just as a task can block on an intermediary object such as a semaphore to wait for that semaphore to be available, a task can block on a task notification to wait for that notification’s state to become pending

Performance Benefits

1	Unblocking an RTOS task with a direct notification is 45% faster * and uses less RAM than unblocking a task using an intermediary object such as a binary semaphore

Usage Restrictions

1	RTOS task notifications can only be used when there is only one task that can be the recipient of the event

通知

1	vim main.cpp

#include <Arduino.h>
 
void sender(void *pvParameters);
void receiver(void *pvParameters);

TaskHandle_t receiverHandler = NULL;

void setup() {
    xTaskCreate(&sender, "sender", 2048, NULL, 1, NULL);
    xTaskCreate(&receiver, "receiver", 2048, NULL, 1, &receiverHandler);
}

void loop() {
    // implicit invocation of vTaskStartScheduler
}

void sender(void *pvParameters) {
    for( ;; ) {
        if (receiverHandler == NULL) {
            vTaskDelay(1000 / portTICK_PERIOD_MS);
            continue;
        }

        xTaskNotify(receiverHandler, (1 << 0), eSetBits);
        xTaskNotify(receiverHandler, (1 << 1), eSetBits);
        vTaskDelay(1000 / portTICK_PERIOD_MS);
        xTaskNotify(receiverHandler, (1 << 2), eSetBits);
        xTaskNotify(receiverHandler, (1 << 3), eSetBits);
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}

void receiver(void *pvParameters) {
    uint32_t state;

    for( ;; ) {
        xTaskNotifyWait(0xffffffff, 0, &state, portMAX_DELAY);
        printf("received state %d times\n", state);
    }
}

问题

when can we not use task notificatin as binary semaphore

One key difference is that any task can wait for an take a binary semaphore, but only the specific task can wait for a specific notification, so a direct to task notification can’t replace a semaphore if you don’t know what task is going to want to wait for it, or perhaps you need to publish somewhere what task is waiting for the event.

参考

0%