From 72a5674c03e6749263e61751616b05b3be80e7cc Mon Sep 17 00:00:00 2001 From: whitequark Date: Thu, 5 Dec 2019 09:39:34 +0000 Subject: [PATCH] manual: document $dffe, $dffsr, $_DFFE_*, $_DFFSR_* cells. --- manual/CHAPTER_CellLib.tex | 101 +++++++++++++++++++++++++++++++++---- 1 file changed, 90 insertions(+), 11 deletions(-) diff --git a/manual/CHAPTER_CellLib.tex b/manual/CHAPTER_CellLib.tex index 0106059b6..6367a4b37 100644 --- a/manual/CHAPTER_CellLib.tex +++ b/manual/CHAPTER_CellLib.tex @@ -177,8 +177,8 @@ Verilog & Cell Type \\ \subsection{Registers} -D-Type Flip-Flops are represented by {\tt \$dff} cells. These cells have a clock port \B{CLK}, -an input port \B{D} and an output port \B{Q}. The following parameters are available for \$dff +D-type flip-flops are represented by {\tt \$dff} cells. These cells have a clock port \B{CLK}, +an input port \B{D} and an output port \B{Q}. The following parameters are available for {\tt \$dff} cells: \begin{itemize} @@ -190,13 +190,23 @@ Clock is active on the positive edge if this parameter has the value {\tt 1'b1} edge if this parameter is {\tt 1'b0}. \end{itemize} -D-Type Flip-Flops with asynchronous resets are represented by {\tt \$adff} cells. As the {\tt \$dff} +D-type flip-flops with enable are represented by {\tt \$dffe} cells. As the {\tt \$dff} +cells they have \B{CLK}, \B{D} and \B{Q} ports. In addition they also have a single-bit \B{EN} +input port for the enable pin and the following parameter: + +\begin{itemize} +\item \B{EN\_POLARITY} \\ +The enable input is active-high if this parameter has the value {\tt 1'b1} and active-low +if this parameter is {\tt 1'b0}. +\end{itemize} + +D-type flip-flops with asynchronous reset are represented by {\tt \$adff} cells. As the {\tt \$dff} cells they have \B{CLK}, \B{D} and \B{Q} ports. In addition they also have a single-bit \B{ARST} input port for the reset pin and the following additional two parameters: \begin{itemize} \item \B{ARST\_POLARITY} \\ -The asynchronous reset is high-active if this parameter has the value {\tt 1'b1} and low-active +The asynchronous reset is active-high if this parameter has the value {\tt 1'b1} and active-low if this parameter is {\tt 1'b0}. \item \B{ARST\_VALUE} \\ @@ -210,8 +220,27 @@ Usually these cells are generated by the {\tt proc} pass using the information in the designs RTLIL::Process objects. \end{sloppypar} +D-type flip-flops with asynchronous set and reset are represented by {\tt \$dffsr} cells. +As the {\tt \$dff} cells they have \B{CLK}, \B{D} and \B{Q} ports. In addition they also have +a single-bit \B{SET} input port for the set pin, a single-bit \B{CLR} input port for the reset pin, +and the following two parameters: + +\begin{itemize} +\item \B{SET\_POLARITY} \\ +The set input is active-high if this parameter has the value {\tt 1'b1} and active-low +if this parameter is {\tt 1'b0}. + +\item \B{CLR\_POLARITY} \\ +The reset input is active-high if this parameter has the value {\tt 1'b1} and active-low +if this parameter is {\tt 1'b0}. +\end{itemize} + +When both the set and reset inputs of a {\tt \$dffsr} cell are active, the reset input takes +precedence. + \begin{fixme} -Add information about {\tt \$sr} cells (set-reset flip-flops) and d-type latches. +Add information about {\tt \$sr} cells (set-reset flip-flops), {\tt \$dlatch} cells (d-type latches), +and {\tt \$dlatchsr} cells (d-type latches with set/reset). \end{fixme} \subsection{Memories} @@ -430,6 +459,30 @@ $ClkEdge$ & $RstLvl$ & $RstVal$ & Cell Type \\ \lstinline[language=Verilog];posedge; & \lstinline[language=Verilog];1; & \lstinline[language=Verilog];0; & {\tt \$\_DFF\_PP0\_} \\ \lstinline[language=Verilog];posedge; & \lstinline[language=Verilog];1; & \lstinline[language=Verilog];1; & {\tt \$\_DFF\_PP1\_} \\ \end{tabular} +% FIXME: the layout of this is broken and I have no idea how to fix it +\hfil +\begin{tabular}[t]{lll} +$ClkEdge$ & $EnLvl$ & Cell Type \\ +\hline +\lstinline[language=Verilog];negedge; & \lstinline[language=Verilog];0; & {\tt \$\_DFFE\_NN\_} \\ +\lstinline[language=Verilog];negedge; & \lstinline[language=Verilog];1; & {\tt \$\_DFFE\_NP\_} \\ +\lstinline[language=Verilog];posedge; & \lstinline[language=Verilog];0; & {\tt \$\_DFFE\_PN\_} \\ +\lstinline[language=Verilog];posedge; & \lstinline[language=Verilog];1; & {\tt \$\_DFFE\_PP\_} \\ +\end{tabular} +% FIXME: the layout of this is broken too +\hfil +\begin{tabular}[t]{llll} +$ClkEdge$ & $SetLvl$ & $RstLvl$ & Cell Type \\ +\hline +\lstinline[language=Verilog];negedge; & \lstinline[language=Verilog];0; & \lstinline[language=Verilog];0; & {\tt \$\_DFFSR\_NNN\_} \\ +\lstinline[language=Verilog];negedge; & \lstinline[language=Verilog];0; & \lstinline[language=Verilog];1; & {\tt \$\_DFFSR\_NNP\_} \\ +\lstinline[language=Verilog];negedge; & \lstinline[language=Verilog];1; & \lstinline[language=Verilog];0; & {\tt \$\_DFFSR\_NPN\_} \\ +\lstinline[language=Verilog];negedge; & \lstinline[language=Verilog];1; & \lstinline[language=Verilog];1; & {\tt \$\_DFFSR\_NPP\_} \\ +\lstinline[language=Verilog];posedge; & \lstinline[language=Verilog];0; & \lstinline[language=Verilog];0; & {\tt \$\_DFFSR\_PNN\_} \\ +\lstinline[language=Verilog];posedge; & \lstinline[language=Verilog];0; & \lstinline[language=Verilog];1; & {\tt \$\_DFFSR\_PNP\_} \\ +\lstinline[language=Verilog];posedge; & \lstinline[language=Verilog];1; & \lstinline[language=Verilog];0; & {\tt \$\_DFFSR\_PPN\_} \\ +\lstinline[language=Verilog];posedge; & \lstinline[language=Verilog];1; & \lstinline[language=Verilog];1; & {\tt \$\_DFFSR\_PPP\_} \\ +\end{tabular} \caption{Cell types for gate level logic networks} \label{tab:CellLib_gates} \end{table} @@ -438,11 +491,22 @@ Table~\ref{tab:CellLib_gates} lists all cell types used for gate level logic. Th {\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 \$\_DFFE\_NN\_}, {\tt \$\_DFFE\_NP\_}, {\tt \$\_DFFE\_PN\_} and {\tt \$\_DFFE\_PP\_} +implement d-type flip-flops with enable. The values in the table for these cell types relate to the +following Verilog code template. + +\begin{lstlisting}[mathescape,language=Verilog] + always @($ClkEdge$ C) + if (EN == $EnLvl$) + Q <= D; +\end{lstlisting} + 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 -d-type flip-flops with asynchronous resets. The values in the table for these cell types relate to the +d-type flip-flops with asynchronous reset. The values in the table for these cell types relate to the following Verilog code template, where \lstinline[mathescape,language=Verilog];$RstEdge$; is \lstinline[language=Verilog];posedge; if \lstinline[mathescape,language=Verilog];$RstLvl$; if \lstinline[language=Verilog];1;, and \lstinline[language=Verilog];negedge; otherwise. @@ -455,6 +519,25 @@ otherwise. Q <= D; \end{lstlisting} +The cell types {\tt \$\_DFFSR\_NNN\_}, {\tt \$\_DFFSR\_NNP\_}, {\tt \$\_DFFSR\_NPN\_}, {\tt \$\_DFFSR\_NPP\_}, +{\tt \$\_DFFSR\_PNN\_}, {\tt \$\_DFFSR\_PNP\_}, {\tt \$\_DFFSR\_PPN\_} and {\tt \$\_DFFSR\_PPP\_} implement +d-type flip-flops with asynchronous set and reset. The values in the table for these cell types relate to the +following Verilog code template, where \lstinline[mathescape,language=Verilog];$RstEdge$; is \lstinline[language=Verilog];posedge; +if \lstinline[mathescape,language=Verilog];$RstLvl$; if \lstinline[language=Verilog];1;, \lstinline[language=Verilog];negedge; +otherwise, and \lstinline[mathescape,language=Verilog];$SetEdge$; is \lstinline[language=Verilog];posedge; +if \lstinline[mathescape,language=Verilog];$SetLvl$; if \lstinline[language=Verilog];1;, \lstinline[language=Verilog];negedge; +otherwise. + +\begin{lstlisting}[mathescape,language=Verilog] + always @($ClkEdge$ C, $RstEdge$ R, $SetEdge$ S) + if (R == $RstLvl$) + Q <= 0; + else if (S == $SetLvl$) + Q <= 1; + else + Q <= D; +\end{lstlisting} + In most cases gate level logic networks are created from RTL networks using the {\tt techmap} pass. The flip-flop cells from the gate level logic network can be mapped to physical flip-flop cells from a Liberty file using the {\tt dfflibmap} pass. The combinatorial logic cells can be mapped to physical cells from a Liberty file via ABC \citeweblink{ABC} @@ -486,11 +569,7 @@ Add information about {\tt \$ff} and {\tt \$\_FF\_} cells. \end{fixme} \begin{fixme} -Add information about {\tt \$dffe}, {\tt \$dffsr}, {\tt \$dlatch}, and {\tt \$dlatchsr} cells. -\end{fixme} - -\begin{fixme} -Add information about {\tt \$\_DFFE\_??\_}, {\tt \$\_DFFSR\_???\_}, {\tt \$\_DLATCH\_?\_}, and {\tt \$\_DLATCHSR\_???\_} cells. +Add information about {\tt \$\_DLATCH\_?\_}, and {\tt \$\_DLATCHSR\_???\_} cells. \end{fixme} \begin{fixme} -- 2.30.2