Initial import of publishing example from micro_ros_arduino.

Author: aentinger

examples/micro-ros_publisher/README.md

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+### Install
+#### ROS2 Galactic
+https://docs.ros.org/en/galactic/Installation/Ubuntu-Install-Debians.html
+#### Install colcon
+https://colcon.readthedocs.io/en/released/user/installation.html
+#### Micro-ROS Tooling
+https://micro.ros.org/docs/tutorials/core/teensy_with_arduino/
+
+
+the final command to start the partner tool
+
+ros2 run micro_ros_agent micro_ros_agent serial --dev /dev/ttyACM0

examples/micro-ros_publisher/micro-ros_publisher.ino

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+#include <micro_ros_arduino.h>
+
+#include <stdio.h>
+#include <rcl/rcl.h>
+#include <rcl/error_handling.h>
+#include <rclc/rclc.h>
+#include <rclc/executor.h>
+
+#include <std_msgs/msg/int32.h>
+
+rcl_publisher_t publisher;
+std_msgs__msg__Int32 msg;
+rclc_executor_t executor;
+rclc_support_t support;
+rcl_allocator_t allocator;
+rcl_node_t node;
+rcl_timer_t timer;
+
+#define LED_PIN 13
+
+#define RCCHECK(fn) { rcl_ret_t temp_rc = fn; if((temp_rc != RCL_RET_OK)){error_loop();}}
+#define RCSOFTCHECK(fn) { rcl_ret_t temp_rc = fn; if((temp_rc != RCL_RET_OK)){}}
+
+
+void error_loop(){
+  while(1){
+    digitalWrite(LED_PIN, !digitalRead(LED_PIN));
+    delay(100);
+  }
+}
+
+void timer_callback(rcl_timer_t * timer, int64_t last_call_time)
+{  
+  RCLC_UNUSED(last_call_time);
+  if (timer != NULL) {
+    RCSOFTCHECK(rcl_publish(&publisher, &msg, NULL));
+    msg.data++;
+  }
+}
+
+void setup() {
+  set_microros_transports();
+  
+  pinMode(LED_PIN, OUTPUT);
+  digitalWrite(LED_PIN, HIGH);  
+  
+  delay(2000);
+
+  allocator = rcl_get_default_allocator();
+
+  //create init_options
+  RCCHECK(rclc_support_init(&support, 0, NULL, &allocator));
+
+  // create node
+  RCCHECK(rclc_node_init_default(&node, "micro_ros_arduino_node", "", &support));
+
+  // create publisher
+  RCCHECK(rclc_publisher_init_default(
+    &publisher,
+    &node,
+    ROSIDL_GET_MSG_TYPE_SUPPORT(std_msgs, msg, Int32),
+    "micro_ros_arduino_node_publisher"));
+
+  // create timer,
+  const unsigned int timer_timeout = 1000;
+  RCCHECK(rclc_timer_init_default(
+    &timer,
+    &support,
+    RCL_MS_TO_NS(timer_timeout),
+    timer_callback));
+
+  // create executor
+  RCCHECK(rclc_executor_init(&executor, &support.context, 1, &allocator));
+  RCCHECK(rclc_executor_add_timer(&executor, &timer));
+
+  msg.data = 0;
+}
+
+void loop() {
+  delay(100);
+  RCSOFTCHECK(rclc_executor_spin_some(&executor, RCL_MS_TO_NS(100)));
+}