[ros-users] ROS Serial C / ROS embedded

Peter Rudolph semael23 at gmail.com
Sat Apr 27 09:24:17 UTC 2013

Hi Everyone,

Due to having no Arduino, but willing to test the connection from an
embedded system to a ros-host, i have written a message generator,
generating C message-header files compatible to standard ros_serial
messages. Also I have written a small version of ros lib, containing types
and function mechanisms to build up a simple node on an embedded system, in
the same style its written on host-machines.

Following Code is part of my example project running on a STM32F3Discovery,
containing accelerometers, magnetometers and gyroscopes, it represents a
ROS-IMU sensor. The board is available for 15-20$ I think, me got it from
embeddedWorld fair this year.

int main(void)
  /* init hardware */
  /* initialize IMU */
  /* initialize ROS, namespace "imu_sensor*/
  /* get pointer to global nodehandle */
  rosNodeHandle_t* nh = rosNodeHandle();
  /* setup ROS IMU message */
  Imu_t imu_msg = rosCreateImu_t();
  /* advertise imu msg */
  rosPublisher_t *imu_pub = nh->advertise(&imu_msg.mh, "/Imu", 512);
  /* set frame id */
  imu_msg.header.frame_id = "/base_link";
  /* enter loop */
  while (rosOk())
    /* update IMU data */
    /* set data to imu message */
    float* acc = imuGetAcc();
    float* mag = imuGetMag();
    float* gyr = imuGetGyr();
    float* ori = imuGetOrientation();
    imu_msg.angular_velocity.x = gyr[X];
    imu_msg.angular_velocity.y = gyr[Y];
    imu_msg.angular_velocity.z = gyr[Z];
    imu_msg.linear_acceleration.x = acc[X];
    imu_msg.linear_acceleration.y = acc[Y];
    imu_msg.linear_acceleration.z = acc[Z];
    imu_msg.orientation.w = ori[W];
    imu_msg.orientation.x = ori[X];
    imu_msg.orientation.y = ori[Y];
    imu_msg.orientation.z = ori[Z];
    /* set timestamp */
    imu_msg.header.stamp = rosTimeNow();
    /* publish message */
    /* spin nodehandle */
    /* sleep 50 milliseconds */

Library code and generated code are at least C99 compatible. Heap size used
is determined by in-/out-buffer lengths like its done in standard
ros_serial. Input is bufferd by a fifo-queue and processed via rosSpin() or
rosSpinOnce() function (same way ros_serial does). Therefor the code could
be usable for any controller understanding C, having a U(S)ART and at least
4K memory.

Currently I'm trying to bring up a FreeRTOS-ROS system, to have another way
to implement sensors or something else.

Now my question is, what shall i do? Put it into ros_serial? Or shall i
make a new ros_embedded package? Or are there already plans to build up an
embedded distribution on RTOS systems, like FreeRTOS?

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