feat(hello_world): add example hello_world from esp-idf and modify it for ESP8266

Commit ID: b0456cc9

examples/get-started/hello_world/main/CMakeLists.txt

@@ -0,0 +1,2 @@
+idf_component_register(SRCS "hello_world_main.c"
+                    INCLUDE_DIRS "")

examples/get-started/hello_world/main/component.mk

@@ -0,0 +1,5 @@
+#
+# "main" pseudo-component makefile.
+#
+# (Uses default behaviour of compiling all source files in directory, adding 'include' to include path.)
+

examples/get-started/hello_world/main/hello_world_main.c

@@ -0,0 +1,38 @@
+/* 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 "esp_spi_flash.h"
+
+
+void app_main()
+{
+    printf("Hello world!\n");
+
+    /* Print chip information */
+    esp_chip_info_t chip_info;
+    esp_chip_info(&chip_info);
+    printf("This is ESP8266 chip with %d CPU cores, WiFi, ",
+            chip_info.cores);
+
+    printf("silicon revision %d, ", chip_info.revision);
+
+    printf("%dMB %s flash\n", spi_flash_get_chip_size() / (1024 * 1024),
+            (chip_info.features & CHIP_FEATURE_EMB_FLASH) ? "embedded" : "external");
+
+    for (int i = 10; i >= 0; i--) {
+        printf("Restarting in %d seconds...\n", i);
+        vTaskDelay(1000 / portTICK_PERIOD_MS);
+    }
+    printf("Restarting now.\n");
+    fflush(stdout);
+    esp_restart();
+}