CAN Packet (Bi-Direction, Firmware ↔︎ ROS driver)

The Main Controller communicates with the specified sub-controller (Top Controller) through a CAN interface.
The CAN Packet serves as the communication medium for this interface and is utilized for two primary purposes:
- Reporting: Forwarding status and measurement data from the Top Controller to the ROS driver. This report packet is transmitted from the firmware to the ROS driver via UDP port 49166.
The transmission interval varies depending on the Virtual Device ID.
- Control: Delivering command instructions from the ROS driver to peripheral devices managed by the Top Controller.
This command packet must be sent from the ROS driver to the firmware through UDP port number 49165.

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Field Layout

The firmware and the ROS driver share the same packet structure for the CAN packet.

Byte Offset	Field Name	Type	Size (Bytes)	Description
0 - 3	Header	Non-Timestamp Header	4	Please refer to Non-Timestamp Header.
4 - 7	CAN id	32-bit unsigned integer	4	Please refer to Extended CAN ID specification.
8	RTR	unsigned char	1	This field specifies the Remote Transmission Request (RTR) frame type of the CAN interface. 0: Data frame 1: Remote frame Currently, only the Data frame (0) is used.
9	IDE	unsigned char	1	CAN Id type. 0: Standard Id 1: Extended Id Currently, only the Extended Id (1) is used.
10	DLC	unsigned char	1	Data length from the CAN data frame. Maximum = 8
11 - 18	Data[8]	unsigned char array	8	Data field of the CAN frame.

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Extended CAN ID Specification

• Priority

  • Defines the arbitration priority of the packet.

  • Lower numerical values indicate higher priority on the CAN bus:
    0x00: Highest
    0x02: High
    0x04: Medium
    0x10: Low
    0x1F: Lowest

• Virtual Device ID

  • Identifies the logical or virtual device associated with this packet.
  • Please refer to the Virtual Device ID List for the mapping.

• Function

  • Specifies the function or message type of the packet (e.g., Set, Report).

• D

  • Indicates the communication direction:
    0: ROS driver → Firmware
    1: Firmware → ROS driver

• Node Id

  • Identifies the node on the CAN network.
  • A fixed value of 0x2 is used in this implementation.

Virtual Device ID List

Device ID	Name	Functions	Priority	DLC	Data Layout	Description
0x000	Version	0x1: Query (ROS driver → Firmware) / Response (Firmware → ROS driver)	Low	0 for Query 4 for Response	Query: Data[0 - 7] Set to 0. Response: Data[0] - Major Data[1] - Minor Data[2] - Revision Data[3] - Build Data[4 - 7] - Set to 0.	This device uses only one function code (0x1). The distinction between a query and a response is made by the Direction (D) bit in the CAN ID.
0x020	Power Monitor	0x1: Report (Firmware → ROS driver)	High	8	Data[0] ~ [3] - 32-bit float electric current value[A] of the main power line Data[4] ~ [7] - 32-bit float electric voltage value[V] of the main power line All values are LSB (Little Endian).	This device measures and reports the current and voltage of the Top Controller's main power line at 100 ms intervals.
0x040	Tower Light	0x1: Report (Firmware → ROS driver) 0x2: Set new state	Medium	1	Bit 0 - Red Bit 1 - Green Bit 2 - Orange(Yellow) Bit 3 ~ 7 - Reserved (must be set to 0) LSB 0 - OFF 1 - ON	This device can control the tower light of the robot.

Usage

To receive CAN report packets from the firmware, the ROS driver must first send a COMS_COMMAND_ENABLE_CAN_COMM command packet. Without this command, the firmware will not transmit CAN report packets.

• Version
  When the ROS driver transmits a Query command, the firmware responds with the version information.

• Power Monitor
  No explicit Query command is required. Voltage and current values of the Top Controller’s power line are reported automatically at 100 ms intervals.

• Tower Light
  The current state of the Tower Light is reported at 100 ms intervals.
  To change the Tower Light state, the ROS driver must send a Set new state function code along with the desired data. The firmware does not generate a dedicated response packet; instead, the updated state can be confirmed through the subsequent periodic report.