06_heartbeats.tex

\section{Heartbeats}\label{sec:heartbeats}
Heartbeats ensure that the system does not reach a state where it is still dangerous to physically handle but 
not accessible through CAN messages. The \texttt{heartbeat\_req} message sent from the server contains a continuously increasing counter.
The counter value is unique to each node. Upon receiving the \texttt{heartbeat\_req} a node responds with a \texttt{heartbeat\_res}, containing the old heartbeat value increased by 1. The heartbeat value is initialized to 0. If a node does not receive \texttt{heartbeat\_req} messages, it will default
to a safe state. Similarly, the server takes note of any unresponsive nodes.