Introduction
Awesomebus1 is a high-speed realtime network for controlling robot actuators. It was designed as an ‘Ethercat-lite’. It features:
- Standard 100Mb Ethernet physical layer
- Up to 25 nodes per bus
- 1KHz+ control loop
- 5us per-node latency
System
An Awesomebus network is composed of a single host device connected to a number of nodes via daisy-chained Ethernet cables (a node has 2 Ethernet ports). Each node drives one or more actuators.
The host device is typically an embedded PC with onboard Ethernet. Our standard setup is based on the Beaglebone, but we also test on normal X86 Linux PCs.
Sitting between the host and the first node is a Power-over-Ethernet (PoE) injector, which is used to power the logic on the nodes. High current actuator supplies are wired separately.
Bus Protocol
See the separate protocol page.
Node Hardware
Each node consists of two or more boards. The node board contains the hardware necessary to interface to the Awesomebus network, while the driver board provides the hardware to drive and interface with any actuator hardware.
Node Board
The node board consists of 3 main subsystems:
- Power regulation - 24V PoE to 3.3V and 1.0V regulation
- Awesomebus interface - Ethernet connectors and PHY connected to an Awesomebus MAC implement in an XMOS
- Node-Driver bridge - an ARM microcontroller which handles communication between the Awesomebus MAC and the driver board.
Awesomebus Node Board
Driver Board
The driver board varies depending on the specific actuator hardware being driven. Currently we have a generic breakout board with an ARM microcontroller to experiment with interfacing to various actuator/sensor hardware.
Node Firmware
The node firmware provides a basic register-based interface to the node and driver board functions.
The node is programmed in Pindakaas, which provides an interactive prompt for rapid development live on the node (via JTAG on the M3 CPU).
Host Software
Since Awesomebus is based on standard Ethernet, the bus is directly accessible from Linux userspace using raw sockets (SOCK_RAW). Where possible we use a kernel with realtime patches for consistent timing of control loops running on the host.
Awesomed
Awesomed is a daemon process which provides a shared-memory interface to the bus. This allows for efficient node register read/write commands from control loop processes.
Libabclient
Libabclient is a wrapper around awesomed for implementing control loop code. It provides a high-level bus interface to control nodes. Currently we have implemented libabclient-java, libabclient-c, and libabclient-python.
Sources
Host-side awesomebus sources are available on Bitbucket