ch14.2.htm

介绍asci设计的一本书

if</B>
 (i = 0) <B CLASS="Keyword">
generate</B>
 </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49019">
 </A>
	IR_LSB: IR_cell <B CLASS="Keyword">
port</B>
 <B CLASS="Keyword">
map</B>
 (shiftIR, Vdd, int_scan(i), </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49020">
 </A>
	clockIR, updateIR, reset_bar, nTRST, Vdd, data_out(i), scan_out);</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49021">
 </A>
<B CLASS="Keyword">
end</B>
 <B CLASS="Keyword">
generate</B>
;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49022">
 </A>
SECOND : <B CLASS="Keyword">
if</B>
 ((i = 1) <B CLASS="Keyword">
and</B>
 (data_in'HIGH &gt; 1)) <B CLASS="Keyword">
generate</B>
</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49023">
 </A>
	IR1 : IR_cell <B CLASS="Keyword">
port</B>
 <B CLASS="Keyword">
map</B>
 (shiftIR, GND, int_scan(i),</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49024">
 </A>
	clockIR, updateIR, reset_bar, nTRST, Vdd, data_out(i), int_scan(i-1));</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49025">
 </A>
<B CLASS="Keyword">
end</B>
 <B CLASS="Keyword">
generate</B>
;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49026">
 </A>
MIDDLE : <B CLASS="Keyword">
if</B>
 ((i &lt; data_in'HIGH) <B CLASS="Keyword">
and</B>
 (i &gt; 1)) <B CLASS="Keyword">
generate</B>
</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49027">
 </A>
	IRi : IR_cell <B CLASS="Keyword">
port</B>
 <B CLASS="Keyword">
map</B>
 (shiftIR, data_in(i), int_scan(i),</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49028">
 </A>
	clockIR, updateIR, reset_bar, nTRST, Vdd, data_out(i), int_scan(i-1));</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49029">
 </A>
<B CLASS="Keyword">
end</B>
 <B CLASS="Keyword">
generate</B>
;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49030">
 </A>
LAST : <B CLASS="Keyword">
if</B>
 (i = data_in'HIGH) <B CLASS="Keyword">
generate</B>
</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49031">
 </A>
	IR_MSB : IR_cell <B CLASS="Keyword">
port</B>
 <B CLASS="Keyword">
map</B>
 (shiftIR, data_in(i), scan_in, </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49032">
 </A>
	clockIR, updateIR, reset_bar, nTRST, Vdd, data_out(i), int_scan(i-1));</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49033">
 </A>
<B CLASS="Keyword">
end</B>
 <B CLASS="Keyword">
generate</B>
; <B CLASS="Keyword">
end</B>
 <B CLASS="Keyword">
generate</B>
 ;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=49034">
 </A>
<B CLASS="Keyword">
end</B>
 structure;</P>
<P CLASS="Computer">
<A NAME="pgfId=117337">
 </A>
&nbsp;</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableFigureTitle">
<A NAME="pgfId=117329">
 </A>
FIGURE&nbsp;14.6&nbsp;<A NAME="28285">
 </A>
An IR (instruction register).</P>
</TD>
</TR>
</TABLE>
</DIV>
<DIV>
<H2 CLASS="Heading2">
<A NAME="pgfId=124969">
 </A>
14.2.3&nbsp;Instruction Decoder</H2>
<P CLASS="BodyAfterHead">
<A NAME="pgfId=124975">
 </A>
<A HREF="CH14.2.htm#19235" CLASS="XRef">
Table 14.4</A>
 shows an <SPAN CLASS="Definition">
instruction decoder</SPAN>
<A NAME="marker=124974">
 </A>
. This model is capable of decoding the following minimum set of boundary-scan instructions:</P>
<OL>
<LI CLASS="NumberFirst">
<A NAME="pgfId=49496">
 </A>
<SPAN CLASS="BodyComputer">
EXTEST</SPAN>
, external test. Drives a known value onto each output pin to test connections between ASICs.</LI>
<LI CLASS="NumberList">
<A NAME="pgfId=49499">
 </A>
<SPAN CLASS="BodyComputer">
SAMPLE/PRELOAD</SPAN>
 (often abbreviated to <SPAN CLASS="BodyComputer">
SAMPLE</SPAN>
). Performs two functions: first sampling the present input value from input pad during capture; and then preloading the BSC update register output during update (in preparation for an EXTEST instruction, for example).</LI>
<LI CLASS="NumberList">
<A NAME="pgfId=71680">
 </A>
<SPAN CLASS="BodyComputer">
IDCODE</SPAN>
. An optional instruction that allows the <SPAN CLASS="Definition">
device-identification register</SPAN>
<A NAME="marker=71678">
 </A>
 (<A NAME="marker=71707">
 </A>
IDCODE) to be shifted out. The IDCODE TDR is an optional register that allows the tester to query the ASIC for the manufacturer&#8217;s name, part number, and other data that is shifted out on TDO. <SPAN CLASS="BodyComputer">
IDCODE</SPAN>
 defaults to the <SPAN CLASS="BodyComputer">
BYPASS</SPAN>
 instruction if there is no IDCODE TDR. </LI>
<LI CLASS="NumberList">
<A NAME="pgfId=49501">
 </A>
<SPAN CLASS="BodyComputer">
BYPASS</SPAN>
. Selects the single-cell bypass register (instead of the BSR) and allows data to be quickly shifted between ASICs.</LI>
</OL>
<P CLASS="Body">
<A NAME="pgfId=49518">
 </A>
The IEEE 1149.1 standard predefines additional optional instructions and also defines the implementation of custom instructions that may use additional TDRs. </P>
<TABLE>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableTitle">
<A NAME="pgfId=46156">
 </A>
TABLE&nbsp;14.4&nbsp;<A NAME="19235">
 </A>
An IR (instruction register) decoder.</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="ComputerFirstLabel">
<A NAME="pgfId=46163">
 </A>
<B CLASS="Keyword">
entity</B>
 IR_decoder <B CLASS="Keyword">
is</B>
 <B CLASS="Keyword">
generic</B>
 (width : INTEGER := 4); <B CLASS="Keyword">
port</B>
 (</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46165">
 </A>
	shiftDR, clockDR, updateDR : BIT; IR_PO : BIT_VECTOR (width-1 <B CLASS="Keyword">
downto</B>
 0) ;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46205">
 </A>
	test_mode, selectBR, shiftBR, clockBR, shiftBSR, clockBSR, updateBSR : <B CLASS="Keyword">
out</B>
 BIT );</P>
<P CLASS="ComputerLastLabel">
<A NAME="pgfId=46167">
 </A>
<B CLASS="Keyword">
end</B>
 IR_decoder;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46168">
 </A>
<B CLASS="Keyword">
architecture</B>
 behave <B CLASS="Keyword">
of</B>
 IR_decoder <B CLASS="Keyword">
is</B>
</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46237">
 </A>
<B CLASS="Keyword">
type</B>
 INSTRUCTION <B CLASS="Keyword">
is</B>
 (EXTEST, SAMPLE_PRELOAD, IDCODE, BYPASS); </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=50597">
 </A>
<B CLASS="Keyword">
signal</B>
 I : INSTRUCTION;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46175">
 </A>
<B CLASS="Keyword">
begin</B>
 <B CLASS="Keyword">
process</B>
 (IR_PO) <B CLASS="Keyword">
begin</B>
 <B CLASS="Keyword">
case</B>
 BIT_VECTOR'( IR_PO(1), IR_PO(0) ) <B CLASS="Keyword">
is</B>
</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46272">
 </A>
<B CLASS="Keyword">
	when</B>
 &quot;00&quot; =&gt; I &lt;= EXTEST; <B CLASS="Keyword">
when</B>
 &quot;01&quot; =&gt; I &lt;= SAMPLE_PRELOAD;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46280">
 </A>
<B CLASS="Keyword">
	when</B>
 &quot;10&quot; =&gt; I &lt;= IDCODE; <B CLASS="Keyword">
when</B>
 &quot;11&quot; =&gt; I &lt;= BYPASS; </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46248">
 </A>
<B CLASS="Keyword">
end</B>
 <B CLASS="Keyword">
case</B>
; <B CLASS="Keyword">
end</B>
 <B CLASS="Keyword">
process</B>
;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46309">
 </A>
test_mode &lt;= '1' <B CLASS="Keyword">
when</B>
 I = EXTEST <B CLASS="Keyword">
else</B>
 '0';</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46336">
 </A>
selectBR &nbsp;&lt;= '1' <B CLASS="Keyword">
when</B>
 (I = BYPASS <B CLASS="Keyword">
or</B>
 I = IDCODE) <B CLASS="Keyword">
else</B>
 '0'; </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46539">
 </A>
shiftBR &lt;= shiftDR;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46334">
 </A>
clockBR &lt;= clockDR <B CLASS="Keyword">
when</B>
 (I = BYPASS <B CLASS="Keyword">
or</B>
 I = IDCODE) <B CLASS="Keyword">
else</B>
 '1'; </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46540">
 </A>
shiftBSR &lt;= shiftDR;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46359">
 </A>
clockBSR &lt;= clockDR <B CLASS="Keyword">
when</B>
 (I = EXTEST <B CLASS="Keyword">
or</B>
 I = SAMPLE_PRELOAD) <B CLASS="Keyword">
else</B>
 '1';</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46419">
 </A>
updateBSR &lt;= updateDR <B CLASS="Keyword">
when</B>
 (I = EXTEST <B CLASS="Keyword">
or</B>
 I = SAMPLE_PRELOAD) <B CLASS="Keyword">
else</B>
 '0';</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=46193">
 </A>
<B CLASS="Keyword">
end</B>
 behave;</P>
</TD>
</TR>
</TABLE>
</DIV>
<DIV>
<H2 CLASS="Heading2">
<A NAME="pgfId=44576">
 </A>
14.2.4&nbsp;TAP Controller</H2>
<P CLASS="BodyAfterHead">
<A NAME="pgfId=44257">
 </A>
<A HREF="CH14.2.htm#13574" CLASS="XRef">
Figure&nbsp;14.7</A>
 shows the TAP controller finite-state machine. The 16-state diagram contains some symmetry: states with suffix <SPAN CLASS="BodyComputer">
'_DR'</SPAN>
 operate on the data registers and those with suffix <SPAN CLASS="BodyComputer">
'_IR'</SPAN>
 apply to the instruction register. All transitions between states are determined by the <SPAN CLASS="BodyComputer">
TMS</SPAN>
 (test mode select) signal and occur at the rising edge of <SPAN CLASS="BodyComputer">
TCK</SPAN>
, the boundary-scan clock. An optional active-low reset signal, <SPAN CLASS="BodyComputer">
nTRST</SPAN>
 or <SPAN CLASS="BodyComputer">
TRST*</SPAN>
, resets the state machine to the initial state, <SPAN CLASS="BodyComputer">
Reset</SPAN>
. If the dedicated <SPAN CLASS="BodyComputer">
nTRST</SPAN>
 is not used, there must be a power-on reset signal (POR)&#8212;not an existing system reset signal.</P>
<P CLASS="Body">
<A NAME="pgfId=52016">
 </A>
The outputs of the TAP controller are not shown in <A HREF="CH14.2.htm#13574" CLASS="XRef">
Figure&nbsp;14.7</A>
, but are derived from each TAP controller state. The TAP controller operates rather like a four-button digital watch that cycles through several states (alarm, stopwatch, 12 hr / 24 hr, countdown timer, and so on) as you press the buttons. Only the shaded states in <A HREF="CH14.2.htm#13574" CLASS="XRef">
Figure&nbsp;14.7</A>
 affect the ASIC core logic; the other states are intermediate steps. The pause states let the controller jog in place while the tester reloads its memory with a new set of test vectors, for example.</P>
<TABLE>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableFirst">
<A NAME="pgfId=124987">
 </A>
&nbsp;</P>
<DIV>
<IMG SRC="CH14-7.gif">
</DIV>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="ComputerFirstLabel">
<A NAME="pgfId=42457">
 </A>
<B CLASS="Keyword">
use</B>
 work.TAP.<B CLASS="Keyword">
all</B>
; <B CLASS="Keyword">
entity</B>
 TAP_sm_states <B CLASS="Keyword">
is</B>
 </P>
<P CLASS="ComputerLastLabel">
<A NAME="pgfId=42458">
 </A>
<B CLASS="Keyword">
	port</B>
 (TMS, TCK, nTRST : <B CLASS="Keyword">
in</B>
 BIT; S : <B CLASS="Keyword">
out</B>
 TAP_STATE); <B CLASS="Keyword">
end</B>
 TAP_sm_states;</P>
<P CLASS="Computer">
<A NAME="pgfId=117348">
 </A>
&nbsp;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=42460">
 </A>
<B CLASS="Keyword">
architecture</B>
 behave <B CLASS="Keyword">
of</B>
 TAP_sm_states <B CLASS="Keyword">
is</B>
 </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=47697">
 </A>
<B CLASS="Keyword">
type</B>
 STATE_ARRAY <B CLASS="Keyword">
is</B>
 <B CLASS="Keyword">
array</B>
 (TAP_STATE, 0 to 1) <B CLASS="Keyword">
of</B>
 TAP_STATE;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=42461">
 </A>
<B CLASS="Keyword">
constant</B>
 T : STATE_ARRAY := ( (Run_Idle, Reset),</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=42462">
 </A>
(Run_Idle, Select_DR), (Capture_DR, Select_IR), (Shift_DR, Exit1_DR), </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=42463">
 </A>
(Shift_DR, Exit1_DR), (Pause_DR, Update_DR), (Pause_DR, Exit2_DR), </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=42464">
 </A>
(Shift_DR, Update_DR), (Run_Idle, Select_DR), (Capture_IR, Reset), </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=42465">
 </A>
(Shift_IR, Exit1_IR), (Shift_IR, Exit1_IR), (Pause_IR, Update_IR), </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=42466">
 </A>
(Pause_IR, Exit2_IR), (Shift_IR, Update_IR), (Run_idle, Select_DR) );</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=42467">
 </A>
<B CLASS="Keyword">
begin</B>
 <B CLASS="Keyword">
process</B>
 (TCK, nTRST) <B CLASS="Keyword">
variable</B>
 S_i: TAP_STATE; <B CLASS="Keyword">
begin</B>
 </P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=47454">
 </A>
<B CLASS="Keyword">
	if</B>
 ( nTRST = '0' ) <B CLASS="Keyword">
then</B>
 S_i := Reset;</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=42469">
 </A>
<B CLASS="Keyword">
	elsif </B>
( TCK = '1' <B CLASS="Keyword">
and</B>
 TCK'EVENT ) <B CLASS="Keyword">
then </B>
-- transition on +VE clock edge</P>
<P CLASS="ComputerLabel">
<A NAME="pgfId=42470">
 </A>
		<B CLASS="Keyword">