architecture/commmi.tex

   1 The only thing the microcontroller has to communicate back with the server is
   2 an update of the SDS and a request for an SDS value.
   3 Since all SDSs have a numeric identifier the engine can just send a request
   4 message with the identifier to the server. A detailed description of the
   5 message for sending and receiving SDSs is described in
   6 Tables~\ref{tbl:sdssend},~\ref{tbl:sdsrecv}.
   7
   8 As said before, publication of SDS values is not done automatically to save
   9 bandwidth. Therefore the tasks need to have a way of requesting the latest SDS
  10 value and a way of publishing an updated value. This is elaborated more upon in
  11 the next section.\todo{Type safety of SDS access}
  12
  13 \begin{table}[ht]
  14         \centering
  15         \begin{tabular}{ll}
  16                 \toprule
  17                 Bytes & Description\\
  18                 \midrule
  19                 $1$ & SDS send code \verb#'s'#\\
  20                 $2-3$ & SDS identifier as a 16-bit integer\\
  21                 $4-5$ & Length of the message 16-bit integer\\
  22                 $n$ & Value of the SDS identifier\\
  23                 \bottomrule
  24         \end{tabular}
  25         \caption{Message format for a SDS-send operation}\label{tbl:sdssend}
  26 \end{table}
  27
  28 \begin{table}[ht]
  29         \centering
  30         \begin{tabular}{ll}
  31                 \toprule
  32                 Bytes & Description\\
  33                 \midrule
  34                 \multicolumn{2}{c}{\textbf{Request}}\\
  35                 $1$ & SDS send code \verb#'r'#\\
  36                 $2-3$ & SDS identifier as a 16-bit integer\\
  37                 \midrule
  38                 \multicolumn{2}{c}{\textbf{Response}}\\
  39                 $1-2$ & Length of the message as a 16-bit integer\\
  40                 $n$ & Value of the SDS\\
  41                 \bottomrule
  42         \end{tabular}
  43         \caption{Message format for a SDS-receive operation}\label{tbl:sdsrecv}
  44 \end{table}