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Add notes about the use of bit #30 in the add/sub & sr insns.

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John Winans 2020-02-17 17:30:17 -06:00
parent 0f87512cf9
commit a75eca5f5c
2 changed files with 7 additions and 1 deletions
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2
book/insnformats.tex
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@ -1391,7 +1391,7 @@
\begin{scope}[shift={(0,-1.5)}] \begin{scope}[shift={(0,-1.5)}]
\DrawInsnTypeI{0000010abcde00011000001110000011} \DrawInsnTypeI{0100000abcde00011000001110000011}
\pgfmathsetmacro\ArrowNorth{\BitBoxArrowInset} \pgfmathsetmacro\ArrowNorth{\BitBoxArrowInset}
\pgfmathsetmacro\ArrowSouth{-16-\BitBoxArrowInset} \pgfmathsetmacro\ArrowSouth{-16-\BitBoxArrowInset}

6
book/rv32/chapter.tex
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@ -388,6 +388,9 @@ capable of representing numbers twice the magnitude of the 20-bit imm value.
\label{insnformat:rtype} \label{insnformat:rtype}
\DrawInsnTypeRTikz{01000001111100011000001110110011} \DrawInsnTypeRTikz{01000001111100011000001110110011}
Note that bit 30 is used to select between the \verb@add@ and \verb@sub@ instructions
as well as to select between arithmetic and logical shifting.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{I Type} \subsection{I Type}
\label{insnformat:itype} \label{insnformat:itype}
@ -403,6 +406,9 @@ the {\em imm} field is used as an immediate value named {\em shamt}
representing the number of bit positions to shift: representing the number of bit positions to shift:
\label{shamt.i:decode}\DrawInsnOpIShiftTypeDecoding \label{shamt.i:decode}\DrawInsnOpIShiftTypeDecoding
Note that bit 30 is used to select between arithmetic and logical shifting.
%\DrawInsnTypeIShiftTikz{00000000001000011001001110100011} %\DrawInsnTypeIShiftTikz{00000000001000011001001110100011}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%