McNet Main Page

Description

On my robot platform, I have one single board PC communicating with 5 µCs. To ensure a stable operation, I needed some sort of protocol, which is able to be used on several hardware interfaces. In my application, it's a serial connection between the PC and the µC-Master/Router, which is connected to the other controllers via I²C. The data I want to transfer are high-level commands, like for the motor controller, "drive 1m forward with half speed", instead of transferring the raw sensor data to the PC and raw output data back. So i dont need a really fast communication, but it should be reliable, it would be good if no packets get lost. It was also important for me that the network topology is not hard programmed into the nodes, there should be a self-detection for that, because i dont want to mess with such unimportant details :) Last but not least, the whole thing should be easy to use, with just a few lines of code in the main program.

Structure

McNet consists of layers:

• The first layer (L0, Hardware) abstracts the hardware interface and has some mechanisms to ensure that the binary data is transferred correctly. Depending on the hardware, it uses a CRC8 checksum, ACK/NACK feedback, timeouts etc.
• The second layer (L1, Routing) is the core of McNet. Each node has its own global address, independent from the HW interface(s). When the system powers up, the nodes first determine the network topology and build up the routing table choosing the shortest (count of hops) routing path (this also happens when a node is "hot-plugged" into a running network). After this process has finished, the network is ready to transmit binary data packets.
• The third and last layer (L2, Application) just acts as an interface between the main application and L1. It transfers a command byte and corresponding user data with different data types (byte, word, single, string, etc)

Each layer has its own send and receive buffers, so you get a 3-staged packet buffer. So you can process received data or send data while you are receiving the next packet.