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\chapter{RV32/64G Instruction Set Listings}
One goal of the RISC-V project is that it be used as a stable software
development target. For this purpose, we define a combination of a
base ISA (RV32I or RV64I) plus selected standard extensions (IMAFD) as
a ``general-purpose'' ISA, and we use the abbreviation G for the IMAFD
combination of instruction-set extensions. This chapter presents
opcode maps and instruction-set listings for RV32G and RV64G.
\input{opcode-map}
Table~\ref{opcodemap} shows a map of the major opcodes for RVG. Major
opcodes with 3 or more lower bits set are reserved for instruction
lengths greater than 32 bits. Opcodes marked as {\em reserved} should
be avoided for custom instruction set extensions as they might be used
by future standard extensions. Major opcodes marked as {\em custom-0}
and {\em custom-1} will be avoided by future standard extensions and
are recommended for use by custom instruction-set extensions within
the base 32-bit instruction format. The opcodes marked {\em
custom-2/rv128} and {\em custom-3/rv128} are reserved for future use
by RV128, but will otherwise be avoided for standard extensions and so
can also be used for custom instruction-set extensions in RV32 and
RV64.
We believe RV32G and RV64G provide simple but complete instruction
sets for a broad range of general-purpose computing. The optional
compressed instruction set described in Chapter~\ref{compressed} can
be added (forming RV32GC and RV64GC) to improve performance, code
size, and energy efficiency, though with some additional hardware
complexity.
As we move beyond IMAFDC into further instruction set extensions, the
added instructions tend to be more domain-specific and only provide
benefits to a restricted class of applications, e.g., for multimedia
or security. Unlike most commercial ISAs, the RISC-V ISA design
clearly separates the base ISA and broadly applicable standard
extensions from these more specialized additions.
Chapter~\ref{extensions} has a more extensive discussion of ways to
add extensions to the RISC-V ISA.
\input{instr-table}
\FloatBarrier
Table~\ref{rvgcsrnames} lists the CSRs that have
currently been allocated CSR addresses. The timers, counters, and
floating-point CSRs are the only CSRs defined in this specification.
\begin{table}[htb!]
\begin{center}
\begin{tabular}{|l|l|l|l|}
\hline
Number & Privilege & Name & Description \\
\hline
\multicolumn{4}{|c|}{Floating-Point Control and Status Registers} \\
\hline
\tt 0x001 & Read/write &\tt fflags & Floating-Point Accrued Exceptions. \\
\tt 0x002 & Read/write &\tt frm & Floating-Point Dynamic Rounding Mode. \\
\tt 0x003 & Read/write &\tt fcsr & Floating-Point Control and Status
Register ({\tt frm} + {\tt fflags}). \\
\hline
\multicolumn{4}{|c|}{Counters and Timers} \\
\hline
\tt 0xC00 & Read-only &\tt cycle & Cycle counter for RDCYCLE instruction. \\
\tt 0xC01 & Read-only &\tt time & Timer for RDTIME instruction. \\
\tt 0xC02 & Read-only &\tt instret & Instructions-retired counter for RDINSTRET instruction. \\
\tt 0xC80 & Read-only &\tt cycleh & Upper 32 bits of {\tt cycle}, RV32I only. \\
\tt 0xC81 & Read-only &\tt timeh & Upper 32 bits of {\tt time}, RV32I only. \\
\tt 0xC82 & Read-only &\tt instreth & Upper 32 bits of {\tt instret}, RV32I only. \\
\hline
\end{tabular}
\end{center}
\caption{RISC-V control and status register (CSR) address map.}
\label{rvgcsrnames}
\end{table}
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