Palouse RoboSub Docs

guppy_can

Nodes and services to interface with CAN bus through ROS.

Contents

  • can_rx: Node that publishes all CAN frames to topics.
  • can_tx: Service that writes data to CAN bus.

CAN RX

The can_rx node publishes every frame read from the CAN bus to a topic corresponding to its CAN ID. Topics follow the naming convention /can/id_<can_id_hex>, so frames with CAN ID 0x102 will be published to the topic /can/id_0x102.

Message Type

Each CAN ID topic is created with the following CanFrame message type:

uint16 can_id
uint8 len
builtin_interfaces/Time stamp
byte[] data

It is imported from guppy_msgs and can be found at guppy_msgs/msg/CanFrame.msg

Interface Selection

The CAN interface that can_rx listens on is controlled by the interface parameter. By default, it is set to can0. The interface can be hot-swapped without restarting the node using the following command:

ros2 param set can_rx interface <can_interface_name>
# eg. ros2 param set can_rx interface can1

CAN TX

The can_tx service writes data to CAN bus. Nodes will interface with this service directly rather than publishing values to send data over CAN.

Message Type

The service accepts a CAN ID and an array of up to 8 bytes. It returns the number of bytes written to CAN bus as a conformation that the frame was sent. The SendCan definition is the following:

uint8 id
byte[] data
---
uint8 written

It is imported from guppy_msgs and can be found at guppy_msgs/srv/SendCan.srv

Interacting with the Service

First, create a service client:

rclcpp::Client<gupy_msgs::srv::SendCan>::SharedPtr client =
    node->create_client<guppy_msgs::srv::SendCan>("add_two_ints");

Next, create a request:

auto request = std::make_shared<guppy_msgs::srv::SendCan::Request>();
request->id = your_id;
request->data = your_data;

Next, send the request:

auto result = client->async_send_request(request);

Finally, await the result:

rclcpp::spin_until_future_complete(node, result)

Interface Selection

Currently, the interface is hard-coded. It can be changed at src/can_tx.cpp:24.