ch12.4.htm
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<LI CLASS="BulletList">
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20 (5 <SPAN CLASS="Symbol">
¥</SPAN>
4) D flip-flops in instance <SPAN CLASS="BodyComputer">
metric</SPAN>
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</UL>
<P CLASS="Body">
<A NAME="pgfId=252882">
</A>
The total is 24 + 132 + 12 + 20 = 188 D flip-flops, which is the same as the number of <SPAN CLASS="BodyComputer">
dfctnb</SPAN>
cell instances in <A HREF="#17078" CLASS="XRef">
Table 12.7</A>
.</P>
<TABLE>
<TR>
<TD ROWSPAN="1" COLSPAN="2">
<P CLASS="TableTitle">
<A NAME="pgfId=252691">
</A>
TABLE 12.7 <A NAME="17078">
</A>
Number of synthesized flip-flops in the Viterbi ASIC.</P>
</TD>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableFirst">
<A NAME="pgfId=252698">
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Command </P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableFirst">
<A NAME="pgfId=252709">
</A>
Synthesizer output<A HREF="#pgfId=252708" CLASS="footnote">
3</A>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Computer">
<A NAME="pgfId=252718">
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> report area -flat </P>
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<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Computer">
<A NAME="pgfId=252828">
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</P>
<P CLASS="Computer">
<A NAME="pgfId=252829">
</A>
Num Gate Count Tot Gate Width Total</P>
<P CLASS="Computer">
<A NAME="pgfId=252830">
</A>
Cell Name Insts Per Cell Count Per Cell Width</P>
<P CLASS="Computer">
<A NAME="pgfId=252831">
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--------- ----- ---------- -------- -------- --------</P>
<P CLASS="Computer">
<A NAME="pgfId=252832">
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...</P>
<P CLASS="Computer">
<A NAME="pgfId=252834">
</A>
dfctnb 188 5.8 1081.0 55.2 10377.6</P>
<P CLASS="Computer">
<A NAME="pgfId=252835">
</A>
...</P>
<P CLASS="Computer">
<A NAME="pgfId=252846">
</A>
--------- ----- ---------- -------- -------- --------</P>
<P CLASS="Computer">
<A NAME="pgfId=252732">
</A>
Totals: 1383 12716.5 25485.6</P>
</TD>
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</TABLE>
<P CLASS="Body">
<A NAME="pgfId=253314">
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<A HREF="#27256" CLASS="XRef">
Table 12.6</A>
gives the total width of the standard cells in the logic core after logic optimization as 18,048 <SPAN CLASS="Symbol">
m</SPAN>
m. Since the standard-cell height for this library is 72 <SPAN CLASS="Symbol">
l</SPAN>
(21.6<SPAN CLASS="Symbol">
m</SPAN>
m), we can make a first estimate of the total logic cell area as </P>
<TABLE>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=414772">
</A>
(18,048 <SPAN CLASS="Symbol">
m</SPAN>
m) (21.6 <SPAN CLASS="Symbol">
m</SPAN>
m)</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=414774">
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<SPAN CLASS="EquationVariables">
=</SPAN>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnLeft">
<A NAME="pgfId=414776">
</A>
390 k(<SPAN CLASS="Symbol">
m</SPAN>
m)<SUP CLASS="Superscript">
2</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=414908">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnNumber">
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</A>
(12.12)</P>
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</TR>
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<P CLASS="TableEqn">
<A NAME="pgfId=414781">
</A>
</P>
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<P CLASS="TableEqnCenter">
<A NAME="pgfId=414783">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqnCenter">
<A NAME="pgfId=414785">
</A>
<SUP CLASS="Superscript">
</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=414910">
</A>
</P>
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</P>
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</A>
</P>
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<P CLASS="TableEqnCenter">
<A NAME="pgfId=414874">
</A>
390 k(<SPAN CLASS="Symbol">
m</SPAN>
m)<SUP CLASS="Superscript">
2</SUP>
mil<SUP CLASS="Superscript">
2</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=414912">
</A>
</P>
</TD>
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<P CLASS="Table">
<A NAME="pgfId=414861">
</A>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=414799">
</A>
</P>
</TD>
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<SPAN CLASS="Symbol">
ª</SPAN>
</P>
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<A NAME="pgfId=414803">
</A>
––––––––––––––</P>
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<A NAME="pgfId=414914">
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</P>
</TD>
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<A NAME="pgfId=414805">
</A>
</P>
</TD>
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</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
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<A NAME="pgfId=414815">
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(25.4 <SPAN CLASS="Symbol">
m</SPAN>
m)<SUP CLASS="Superscript">
2</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=414916">
</A>
</P>
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<P CLASS="Table">
<A NAME="pgfId=414817">
</A>
</P>
</TD>
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<TR>
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<A NAME="pgfId=414888">
</A>
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600 mil<SUP CLASS="Superscript">
2</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableEqn">
<A NAME="pgfId=414920">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=414829">
</A>
</P>
</TD>
</TR>
</TABLE>
<P CLASS="Body">
<A NAME="pgfId=253337">
</A>
In the physical layout we shall need additional space for routing. The ratio of routing to logic cell area is called the <SPAN CLASS="Definition">
routing factor</SPAN>
<A NAME="marker=253351">
</A>
. The routing factor depends primarily on whether we use two levels or three levels of metal. With two levels of metal the routing factor is typically between 1 and 2. With three levels of metal, where we may use over-the-cell routing, the routing factor is usually zero to 1. We thus expect a logic core area of 600–1000 mils<SUP CLASS="Superscript">
2</SUP>
for the Viterbi decoder using this cell library. </P>
<P CLASS="Body">
<A NAME="pgfId=253533">
</A>
From <A HREF="#27256" CLASS="XRef">
Table 12.6</A>
we see the I/O cells in this library are 100.8 <SPAN CLASS="Symbol">
m</SPAN>
m wide or approximately 4 mil (the width of a single pad site). From the I/O cell data book we find the I/O cell height is 650 <SPAN CLASS="Symbol">
m</SPAN>
m (actually 648.825 <SPAN CLASS="Symbol">
m</SPAN>
m) or approximately 26 mil. Each I/O cell thus occupies 104 mil<SUP CLASS="Superscript">
2</SUP>
. Our 33 pad sites will thus require approximately 3400 mil<SUP CLASS="Superscript">
2</SUP>
which is larger than the estimated core logic area.</P>
<P CLASS="Body">
<A NAME="pgfId=264622">
</A>
Let us go back and take a closer look at what it usually takes to get to this point. Remember we used an already prepared Verilog model for the Viterbi decoder. </P>
</DIV>
<HR>
<DIV CLASS="footnotes">
<DIV CLASS="footnote">
<P CLASS="TableFootnote">
<SPAN CLASS="footnoteNumber">
1.</SPAN>
<A NAME="pgfId=246697">
</A>
See footnote <A HREF="CH12.2.htm#31398" CLASS="XRef">
1</A>
in <A HREF="CH12.2.htm#23004" CLASS="XRef">
Table 12.3</A>
for explanations of the abbreviations used in this table.</P>
</DIV>
<DIV CLASS="footnote">
<P CLASS="TableFootLast">
<SPAN CLASS="footnoteNumber">
2.</SPAN>
<A NAME="pgfId=264841">
</A>
I/O cell height (I/O cells have prefixes <SPAN CLASS="BodyComputer">
pc5</SPAN>
and <SPAN CLASS="BodyComputer">
pv</SPAN>
) is approximately 650 <SPAN CLASS="Symbol">
m</SPAN>
m in this cell library.</P>
</DIV>
<DIV CLASS="footnote">
<P CLASS="TableFootLast">
<SPAN CLASS="footnoteNumber">
3.</SPAN>
<A NAME="pgfId=252708">
</A>
See footnote <A HREF="CH12.2.htm#31398" CLASS="XRef">
1</A>
in <A HREF="CH12.2.htm#23004" CLASS="XRef">
Table 12.3</A>
for explanations of the abbreviations used in this table. Logic cell dfctnb is a D flip-flop with clear in this standard-cell library.</P>
</DIV>
</DIV>
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