Newer
Older
3.2.7 000000000000ce42:779c5443 220600 WR-Periph-1Wire
3.2.8 000000000000ce42:779c5443 220700 WR-Periph-1Wire
\end{verbatim}
\normalsize
\subsection{Endianness Problems}
Please note that the host may have some issues reading the binary
dumps. According to how the bridge between the host and FPGA is
designed you may face one of the following situations:
\begin{itemize}
\item The host is big-endian (data is always correct).
\item The host is little-endian and the bridge is byte-oriented.
\item The host is little-endian and the bridge is word-oriented.
\end{itemize}
If the bridge is byte-oriented, i.e. each and every byte can be
independently addressed as such, then the usual endian conversion
rules apply (e.g. you can \textit{memcpy} the records to host memory
and access fields with endian-aware code).
If the bridge is word-oriented, with 32-bit words in this example, the behaviour is stranger, in
a way. After you copied the data to host memory (whether one byte at
a time or not), you'll find that the bytes are swapped within each word.
This happens because the 32-bit word is transferred as a whole: the least significant
bits remain the the least significant, but they come from offset 3 in the data structure
and are stored at offset 0 in the little-endian host. If this is your case, you need to
byte-swap each 32-bit word before using the structure in a
little-endian host. After such swapping, the data fields live at the correct
offsets and must be accessed as big endian.
\subsection{Existing Tools}
As part of the \textit{Etherbone} project, you already find a number
of tools that work with SDB structures (including \texttt{eb-ls} that
printed the table of devices shown above). The project is at
\texttt{http://www.ohwr.org/projects/etherbone-core} .
