How to pass argument to callback in rclc?
I have a subscription:
rclc_executor_add_subscription(&executor, &data_subscription, &data_msg, &data_callback, ON_NEW_DATA);
But I would like to pass a variable to it. I know in rclcpp, you can use std::bind and rclpy you can you functools.partials but I don't know how to do it in pure C. I tried looking for dynamic variable allocation, and also pass a void* in the callback parameters, but without success.
Can you point me to some example?
Thanks
Asked by Dben on 2022-10-22 18:48:43 UTC
Answers
Hi there, I'm working on a rclc implementation myself on teensy with micro-ROS and the below has worked for me.
I have submitted a pull request on this github repository (still waiting to get merged). https://github.com/micro-ROS/micro_ros_platformio/pull/77
this as a new example This might provide some guidance into the right direction. Note it is loading the address of msg_sub to the pointer that is then used in the callback routine. (I think that's what it does)
Here is the source code:
#include <Arduino.h>
#include <Wire.h>
#include <micro_ros_platformio.h>
#include <rcl/rcl.h>
#include <rclc/rclc.h>
#include <rclc/executor.h>
#include <std_msgs/msg/int32.h>
#if !defined(MICRO_ROS_TRANSPORT_ARDUINO_SERIAL)
#error This example is only avaliable for Arduino framework with serial transport.
#endif
//publisher
rcl_publisher_t publisher;
std_msgs__msg__Int32 msg_pub;
// subscriber
rcl_subscription_t subscriber;
std_msgs__msg__Int32 msg_sub;
// publisher and subscriber common
rcl_node_t node;
rclc_support_t support;
rcl_allocator_t allocator;
rclc_executor_t executor;
rcl_timer_t timer;
unsigned int num_handles = 2; // 1 subscriber, 1 publisher
#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)){}}
// Error handle loop
void error_loop() {
while(1) {
digitalWrite(LED_PIN, !digitalRead(LED_PIN));
delay(500);
}
}
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_pub, NULL));
msg_pub.data++;
}
}
void subscription_callback(const void * msgin)
{
const std_msgs__msg__Int32 * msg = (const std_msgs__msg__Int32 *)msgin;
digitalWrite(LED_PIN, (msg->data == 0) ? LOW : HIGH);
}
void setup() {
// Configure serial transport
Serial.begin(115200);
set_microros_serial_transports(Serial);
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, "uros_platformio_node", "", &support));
// create publisher
RCCHECK(rclc_publisher_init_default(
&publisher,
&node,
ROSIDL_GET_MSG_TYPE_SUPPORT(std_msgs, msg, Int32),
"micro_ros_platformio_node_publisher"));
// create subscriber
RCCHECK(rclc_subscription_init_default(
&subscriber,
&node,
ROSIDL_GET_MSG_TYPE_SUPPORT(std_msgs, msg, Int32),
"micro_ros_platformio_node_subscriber"));
// 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, num_handles, &allocator));
RCCHECK(rclc_executor_add_timer(&executor, &timer));
RCCHECK(rclc_executor_add_subscription(&executor, &subscriber, &msg_sub, &subscription_callback, ON_NEW_DATA));
msg_pub.data = 0;
}
void loop() {
delay(100);
RCSOFTCHECK(rclc_executor_spin_some(&executor, RCL_MS_TO_NS(100)));
}
Asked by PointCloud on 2022-10-23 01:56:22 UTC
Comments
Thanks! My question was more, how do I pass the message type + another variable. Here I can only see the message type being passed. To be clear, let's say an int is published, I want to access this one + my own variable. PS: all maintainers are at roscon, probably not checking PRs right now
Asked by Dben on 2022-10-23 03:46:23 UTC
Is the other "own" variable withing the computer running the subscriber node, and maybe even within that same program? So i understand the int is published, but we don't know yet where the other variable comes from. Same host, and even same program, or external?
If, so, I can maybe see two different ways this could work. 1. global variable (yuck :-) ) 2. create a pointer and pass address reference to the variable, similar to what the subscriber callback uses?
Asked by PointCloud on 2022-10-23 11:40:06 UTC
Yes, same program, and I think the pointer should work and what I wanted to get, but don't know how
Asked by Dben on 2022-10-23 12:54:00 UTC
Comments