How Does Rosette Put an RP2350 + W5100S Board on a ROS 2 Network Without a micro-ROS Agent?

📚 Context: CenteredSolutions/Rosette — a DDSI-RTPS 2.5 stack and rmw implementation for microcontrollers. A stock rclc program on a WIZnet EVB board joins a ROS 2 network directly, next to Fast DDS and Cyclone DDS nodes.

01 — What changes without the agent

With micro-ROS, the agent on a host joins DDS for the board. Rosette puts RTPS on the board itself. The firmware is an unmodified rclc program linked against rmw_rosette. Stock rcl and rclc are still built with micro_ros_setup's generate_lib, but rmw_microxrcedds is never linked.

02 — The chip and the boards

Rosette does not use ioLibrary. It has its own header-only driver, WiznetDevice<Chip, Bus> in ports/net/wiznet/, and on a board the network is the chip's hardware UDP. The board CMake states the result: no RTOS, a cooperative superloop.

03 — Four sockets, three for RTPS

• RTPS holds three sockets for the life of the participant. DHCP and SNTP borrow the fourth only during an exchange; the DHCP client's header notes this "matters on a chip with four hardware sockets".
• RX memory is tilted toward user data. A socket that needs more calls set_receive_buffer_size() before bind().
• When a full 4096-byte sample outgrows the 4 KiB buffer, the reader recovers the lost fragments with NACK_FRAG one heartbeat later.

04 — Multicast and ARP on the chip

The SPDP group socket is configured in device.hpp before it is opened:

write(Chip::socket_dest_hardware(socket), group_mac.data(), group_mac.size());
write(Chip::socket_dest_ip(socket), group.data(), group.size());
write_u16(Chip::socket_dest_port(socket), group_port);
write_u8(Chip::socket_mode(socket),
         static_cast<uint8_t>(Chip::mode_udp() |
                              Chip::mode_multicast() |
                              Chip::mode_igmp_v2()));

05 — 1472 bytes, no IP reassembly

RMW_ROSETTE_STRICT_LINK=1 makes a host drop every datagram over the limit, so the host tests face the board's losses against real stock traffic.

06 — No heap, measured footprint

The RTPS core and rmw_rosette never call malloc or new; every pool is sized at build time, so running out of room shows up at boot, not after a week in the field.

Tests back this up: 152 DDSI-RTPS 2.5 statements in traceability matrices, the WIZnet driver run against a register model of the chip, and CI on Humble and Jazzy against Fast DDS and Cyclone DDS.

07 — Where it stands

• Hardware runs so far: the W5100S-EVB-Pico2 (ROS) and the W6100-EVB-Pico (UDP echo). Discovery multicast on the W6100/W6300 is confirmed when a ROS example first runs there.
• rclcpp nodes talk to Rosette nodes, but cannot load rmw_rosette themselves.
• Firmware samples up to 4096 B by default; IPv4 locators only; no DDS-Security; pre-1.0.

On one wired switch, each controller board becomes a ROS 2 node in its own right, with no PC translating for it.

08 — Similar Projects on WIZnet Makers

• How to Bridge Physical I/O into ROS 2 with W6100 on RP2040? — one of Rosette's boards on the agent route: Zephyr and micro-ROS to an agent on the host.
• mros2-esp32-eth1 — the same no-agent goal on an ESP32-S3, with embeddedRTPS over lwIP and the W5500 as the interface. Rosette hands UDP to the chip instead.
• robo-con-for-Ethernet — a WIZnet board reaching ROS 2 through a command bridge.

Q&A

Q. In what mode is the WIZnet chip used?

Hardware UDP sockets through Rosette's own register driver. No lwIP, no RTOS; RTPS runs on the RP2350 on top.

Q. Does it need a micro-ROS agent?

No. An optional agent backend exists for setups that want one.

Q. Can it be reused?

Apache-2.0. The bundled Pico SDK board headers are BSD-3-Clause.

Original Link: https://github.com/CenteredSolutions/Rosette

WIZnet driver: ports/net/wiznet/device.hpp · RTPS sockets: src/rtps/transport.cpp · Memory: docs/mcu_memory_model.md · Network: docs/network_configuration.md