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Merge pull request #788 from whitequark/master 

Document $tribuf and some gates
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Clifford Wolf 2019-01-15 09:52:01 +01:00 committed by GitHub
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22
manual/CHAPTER_CellLib.tex
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@ -119,6 +119,12 @@ than one bit from \B{S} is set the output is undefined. Cells of this type are u
``parallel cases'' (defined by using the {\tt parallel\_case} attribute or detected by
an optimization).
The {\tt \$tribuf} cell is used to implement tristate logic. Cells of this type have a \B{WIDTH}
parameter and inputs \B{A} and \B{EN} and an output \B{Y}. The \B{A} input and \B{Y} output are
\B{WIDTH} bits wide, and the \B{EN} input is one bit wide. When \B{EN} is 0, the output \B{Y}
is not driven. When \B{EN} is 1, the value from \B{A} input is sent to the \B{Y} output. Therefore,
the {\tt \$tribuf} cell implements the function \lstinline[language=Verilog]; Y = EN ? A : 'bz;.
Behavioural code with cascaded {\tt if-then-else}- and {\tt case}-statements
usually results in trees of multiplexer cells. Many passes (from various
optimizations to FSM extraction) heavily depend on these multiplexer trees to
@ -398,9 +404,15 @@ Verilog & Cell Type \\
\hline
\lstinline[language=Verilog]; Y = ~A; & {\tt \$\_NOT\_} \\
\lstinline[language=Verilog]; Y = A & B; & {\tt \$\_AND\_} \\
\lstinline[language=Verilog]; Y = ~(A & B); & {\tt \$\_NAND\_} \\
\lstinline[language=Verilog]; Y = A & ~B; & {\tt \$\_ANDNOT\_} \\
\lstinline[language=Verilog]; Y = A | B; & {\tt \$\_OR\_} \\
\lstinline[language=Verilog]; Y = ~(A | B); & {\tt \$\_NOR\_} \\
\lstinline[language=Verilog]; Y = A | ~B; & {\tt \$\_ORNOT\_} \\
\lstinline[language=Verilog]; Y = A ^ B; & {\tt \$\_XOR\_} \\
\lstinline[language=Verilog]; Y = ~(A ^ B); & {\tt \$\_XNOR\_} \\
\lstinline[language=Verilog]; Y = S ? B : A; & {\tt \$\_MUX\_} \\
\lstinline[language=Verilog]; Y = EN ? A : 'bz; & {\tt \$\_TBUF\_} \\
\hline
\lstinline[language=Verilog]; always @(negedge C) Q <= D; & {\tt \$\_DFF\_N\_} \\
\lstinline[language=Verilog]; always @(posedge C) Q <= D; & {\tt \$\_DFF\_P\_} \\
@ -423,9 +435,10 @@ $ClkEdge$ & $RstLvl$ & $RstVal$ & Cell Type \\
\end{table}
Table~\ref{tab:CellLib_gates} lists all cell types used for gate level logic. The cell types
{\tt \$\_NOT\_}, {\tt \$\_AND\_}, {\tt \$\_OR\_}, {\tt \$\_XOR\_} and {\tt \$\_MUX\_}
are used to model combinatorial logic. The cell types {\tt \$\_DFF\_N\_} and {\tt \$\_DFF\_P\_}
represent d-type flip-flops.
{\tt \$\_NOT\_}, {\tt \$\_AND\_}, {\tt \$\_NAND\_}, {\tt \$\_ANDNOT\_}, {\tt \$\_OR\_}, {\tt \$\_NOR\_},
{\tt \$\_ORNOT\_}, {\tt \$\_XOR\_}, {\tt \$\_XNOR\_} and {\tt \$\_MUX\_} are used to model combinatorial logic.
The cell type {\tt \$\_TBUF\_} is used to model tristate logic.
The cell types {\tt \$\_DFF\_N\_} and {\tt \$\_DFF\_P\_} represent d-type flip-flops.
The cell types {\tt \$\_DFF\_NN0\_}, {\tt \$\_DFF\_NN1\_}, {\tt \$\_DFF\_NP0\_}, {\tt \$\_DFF\_NP1\_},
{\tt \$\_DFF\_PN0\_}, {\tt \$\_DFF\_PN1\_}, {\tt \$\_DFF\_PP0\_} and {\tt \$\_DFF\_PP1\_} implement
@ -477,7 +490,6 @@ Add information about {\tt \$\_DFFE\_??\_}, {\tt \$\_DFFSR\_???\_}, {\tt \$\_DLA
\end{fixme}
\begin{fixme}
Add information about {\tt \$\_NAND\_}, {\tt \$\_NOR\_}, {\tt \$\_XNOR\_}, {\tt \$\_ANDNOT\_}, {\tt \$\_ORNOT\_},
{\tt \$\_AOI3\_}, {\tt \$\_OAI3\_}, {\tt \$\_AOI4\_}, and {\tt \$\_OAI4\_} cells.
Add information about {\tt \$\_AOI3\_}, {\tt \$\_OAI3\_}, {\tt \$\_AOI4\_}, and {\tt \$\_OAI4\_} cells.
\end{fixme}