\chapter{Preface}

This is version 1.9.1 of the RISC-V privileged architecture
proposal.  Changes from version 1.9 include:

\begin{itemize}
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\item Numerous additions and improvements to the commentary sections.
\item Change configuration string proposal to be use a search process
  that supports various formats including Device Tree String and
  flattened Device Tree.
\item Made {\tt misa} optionally writable to support modifying base
  and supported ISA extensions.  CSR address of {\tt misa} changed.
\item Added description of debug mode and debug CSRs.
\item Added a hardware performance monitoring scheme.  Simplified the
  handling of existing hardware counters, removing privileged versions
  of the counters and the corresponding delta registers.
\item Fixed description of SPIE in presence of user-level interrupts.
\end{itemize}