Difference between revisions of "Hello World with ESP32 Explained"

Revision as of 09:24, 24 December 2016

The Espressif Internet Development Framework (ESP-IDF) uses FreeRTOS to make better use of the two high speed processors and manage the numerous built-in peripherals. It is done by creating tasks. Let's look at the hello world, that looks a little different from the ones that you might have seen.

This hello world prints the string on UART (eventually on the computer terminal). We will first look at the ESP-IDF structure. Then look at the hello world example and modify it blink an LED while still continuously printing the 'hello world' string.

 
			   esp-idf
				|
				|
				+ - - components
				|
				+ - - docs
				|
				+ - - examples
				|
				+ - - make
				|
				+ - - tools

The components directory holds all the 'C' code for the ESP32. It contains all the 'components' that make up the ESP32. It includes Drivers for numerous peripherals, the bootloader, bt(bluetooth), freeRTOS etc. If we expand the components the tree looks like so:

+---components
|   +---app_update
|   |   |   component.mk
|   |   |   esp_ota_ops.c
|   |   |   
|   |   \---include
|   |           esp_ota_ops.h
|   |           
|   +---bootloader
|   |   |   component.mk
|   |   |   README.rst
|   |   |   
|   |   +---include
|   |   |       esp_image_format.h
|   |   |       esp_secure_boot.h
|   |   |       
|   |   +---include_priv
|   |   |       bootloader_flash.h
|   |   |       
|   |   \---src
|   |           bootloader_flash.c
|   |           esp_image_format.c
|   |           secure_boot.c
|   |           secure_boot_signatures.c
|   |           
|   +---bt
|   |   |   bt.c
|   |   |   component.mk
|   |   |   Kconfig
|   |   |   
|   |   +---bluedroid
.   .
.   .
.   . 
|   |           
|   +---driver
|   |   |   component.mk
|   |   |   gpio.c
|   |   |   ledc.c
|   |   |   pcnt.c
|   |   |   periph_ctrl.c
|   |   |   rmt.c
|   |   |   timer.c
|   |   |   uart.c
|   |   |   
|   |   \---include
|   |       \---driver
|   |               gpio.h
|   |               ledc.h
|   |               pcnt.h
|   |               periph_ctrl.h
|   |               rmt.h
|   |               timer.h
|   |               uart.h
|   |               
|   +---esp32
|   |   |   abi.cpp
|   |   |   brownout.c
|   |   |   component.mk
|   |   |   cpu_freq.c
|   |   |   cpu_start.c
|   |   |   cpu_util.c
.	.
.	.
.	.
.	.
|   |           
|   +---esptool_py
|   |   |   Kconfig.projbuild
|   |   |   LICENSE
.   .
.   .
|   |                       
|   +---ethernet
|   |   |   component.mk
.   .
|   |           
|   +---expat
.   . 
|   |               
|   +---freertos
|   |   |   component.mk
|   |   |   croutine.c
|   |   |   event_groups.c
|   |   |   FreeRTOS-openocd.c
|   |   |   heap_regions.c
.   .
.   .
|   |           
|   +---idf_test
.	.
.	.
|	|														
|   +---newlib
.	.
|	|
|   +---nghttp
.	.
.	.
.	.
|	|              
|   +---nvs_flash
|   |   |   .gitignore
|   |   |   component.mk
|   |   |   README.rst
|   |   |   
.	.
.	.
|   |           
|   +---openssl
.	.
.	.          
|   +---partition_table
 
|   |           
|   +---spi_flash
|
|   |           
|   +---tcpip_adapter
 
|   |           
|   +---ulp
|   |           
|   +---vfs
|   |           
|   +---wpa_supplicant
 
|   |               
|   \---xtensa-debug-module
|       |   component.mk
|       |   eri.c
|       |   trax.c
|       |   
|       \---include
|               eri.h
|               trax.h
|               xtensa-debug-module.h

/* Hello World Example
 
   This example code is in the Public Domain (or CC0 licensed, at your option.)
 
   Unless required by applicable law or agreed to in writing, this
   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
   CONDITIONS OF ANY KIND, either express or implied.
*/
#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_system.h"
#include "nvs_flash.h"
 
void hello_task(void *pvParameter)
{
    printf("Hello world!\n");
    for (int i = 10; i >= 0; i--) {
        printf("Restarting in %d seconds...\n", i);
        vTaskDelay(1000 / portTICK_RATE_MS);
    }
    printf("Restarting now.\n");
    fflush(stdout);
    esp_restart();
}
 
void app_main()
{
    nvs_flash_init();
    xTaskCreate(&hello_task, "hello_task", 2048, NULL, 5, NULL);
}