optionsdoc.htm

用VHDL编写的串口异步通信的例子

<p class="whs13">If timing constraints are not set, the 
 program optimizes either for speed or density, depending on the user setting 
 for the <span style="font-weight: bold;"><B>Use Timing Optimization</B></span> 
 option.</p>

<ul>
	
	<ul class=whs1
		style="list-style: disc;"
		type=disc>
		
		<ul class=whs2
			style="list-style: circle;"
			type=circle>
			
			<li class=kadov-p><p class="whs14">If 
 <span style="font-weight: bold;"><B>Use Timing Optimization</B></span> is turned 
 on, the combinatorial logic will be mapped for speed.</p></li>
			
			<li class=kadov-p-Cwhs3><p class=whs3
										style="font-family: arial; font-size: 10pt;">If 
 <span style="font-weight: bold;"><B>Use Timing Optimization</B></span> is turned 
 off, the combinatorial logic will be mapped for density. The goal of optimization 
 will then be to reduce the total number of p-terms.</p></li>
		</ul>
	</ul>
</ul>

<p class="whs15"><font style="font-family: arial; font-size: 10pt;"
									face=arial
									size=2><span style="font-size: 10pt;"><FONT SIZE=2 style="font-size:10pt;">Logic 
 marked with the </FONT></span><span style="font-weight: bold;"><B><b style="font-size: 10pt;">NOREDUCE</b></B></span><span 
 style="font-size: 10pt;"><FONT SIZE=2 style="font-size:10pt;"> property will not be extracted or optimized.</FONT></span></font></p>

<p class=whs3
	style="font-family: arial, sans-serif;
			font-size: 10pt;
			font-weight: bold;
			margin-left: 40px;"><span style="font-family: arial; font-weight: normal;">By 
 default, this option is on.</span> </p>

<ul>
	
	<li class=kadov-p-Cwhs3><p class=whs3
								style="font-family: arial, sans-serif;
										font-size: 10pt;
										font-weight: bold;"><b style="font-weight: bold;"><span 
 style="font-weight: bold;"><B>Use Timing Constraints -- </B></span><span style="font-weight: normal;">This 
 option instructs the fitter use Timing Constraints when fitting the design. 
 <!--kadov_tag{{<spaces>}}-->&nbsp;<!--kadov_tag{{</spaces>}}-->If this 
 box is not checked, the fitter will ignore timing constraints, if necessary.</span></b></p></li>
	
	<li class=kadov-p-Cwhs3><p class=whs3
								style="font-family: arial, sans-serif; font-size: 10pt;"><b 
 style="font-weight: bold;"><span style="font-weight: bold;"><B>Enable WYSIWYG 
 Mode -- (CoolRunner only) </B></span><span style="font-weight: normal;">T</span></b>he 
 goal of the WYSIWYG options is to have a netlist reflect the user's specifications, 
 as much as possible. All the nodes declared in the HDL design are preserved. 
 By default, this property is set to Off (Checkbox is not checked) When 
 this property is On (checkbox is checked), XST:</p></li>
	
	<ul>
		
		<li style="list-style: circle;"
			type=circle
			class=kadov-p-Cwhs3><p class=whs3
									style="font-family: arial, sans-serif; font-size: 10pt;">Preserves 
 all the user internal signals (nodes)</p></li>
		
		<li style="list-style: circle;"
			type=circle
			class=kadov-p-Cwhs3><p class=whs3
									style="font-family: arial, sans-serif; font-size: 10pt;">Creates 
 source_node constraints in NGC file for all these nodes.</p></li>
		
		<li style="list-style: circle;"
			type=circle
			class=kadov-p-Cwhs3><p class=whs3
									style="font-family: arial, sans-serif; font-size: 10pt;">Skips 
 the design optimization (collapse, factorization). Only the Boolean equation 
 minimization is performed.</p></li>
	</ul>
	
	<li class=kadov-p-Cwhs3><p class=whs3
								style="font-family: arial, sans-serif; font-size: 10pt;"><b><span 
 style="font-weight: bold;"><B>Optimization Style</B></span></b>-- The Optimization 
 Method allows you to select from one of two basic optimization strategies: 
 <span style="font-weight: bold;"><B><b>Density</b></B></span> or <span style="font-weight: bold;"><B><b>Speed</b></B></span>. 
 <span style="font-weight: bold;"><B><b>Density</b></B></span> focuses on solely 
 on density, and <span style="font-weight: bold;"><B><b>Speed</b></B></span> focuses 
 solely on speed.</p></li>
	
	<li class=kadov-p><p class="whs16"><span 
 style="font-weight: bold;"><B>Location Constraints</B></span> -- The Try selection 
 will attempt to fit the design with the pin assignments specified in the 
 design source. If the design cannot be fit with these pin assignments, 
 the fitter will remove the location constraints and attempt to fit the 
 design with no location constraints. A warning message will tell the user 
 if the location constraints have been removed.</p></li>
	
	<ul class=whs5
		style="list-style: circle;"
		type=circle>
		
		<li class=kadov-p><p class="whs17">The 
 <span style="font-weight: bold;"><B><b>Try</b></B></span> selection will attempt 
 to fit the design with the pin assignments specified in the design source. 
 If the design cannot be fit with these pin assignments, the fitter will 
 ignore the pin assignments.</p></li>
	</ul>
	
	<li style="list-style: circle;"
		type=circle
		class=kadov-p-Cwhs6><p class=whs6
								style="font-family: arial, sans-serif; font-size: 10pt;">The 
 <span style="font-weight: bold;"><B>On </B></span>selection will attempt to fit 
 the design with the pin assignments specified in the design source. If 
 the design cannot be fit with these pin assignments, the fitter will notify 
 the user that the device could not fit. It will not unlock the pins under 
 this option.</p></li>
	
	<li style="list-style: circle;"
		type=circle
		class=kadov-p-Cwhs7><p class=whs7
								style="font-family: arial, sans-serif; font-size: 10pt;">The 
 <span style="font-weight: bold;"><B>Off</B></span> selection will attempt to 
 fit the design and will ignore the pin assignments specified in the design 
 source. If the design can be fit with no pre-assigned pins, the fitter 
 will assign pins, which can be viewed in the fitter report (filename.fit). 
 The user should take these pin assignments and incorporate them back into 
 the design source file. The user will be notified whether the fitting 
 operation was successful.</p></li>
	
	<li class=kadov-p-Cwhs8><p class=whs8
								style="font-family: arial, sans-serif;
										font-size: 10pt;
										font-weight: bold;"><b><span style="font-weight: bold;"><B>Output 
 Slew Rate -- </B></span></b><span style="font-weight: normal;">Use this option 
 to control the default output slew rate. You can control the transition 
 time of device output pins by setting the slew rate to Slow or Fast. Limiting 
 the slew rate (Slow) reduces output switching surges in the device. The 
 default is Fast.</span></p></li>
</ul>

<p class="whs18"><span style="font-weight: bold;"><B>Note</B></span>: 
 Any explicit slew rate control properties in the design or constraints 
 file take precedence over this Output Slew Rate setting. </p>

<ul>
	
	<li class=kadov-p-Cwhs8><p class=whs8
								style="font-family: arial, sans-serif;
										font-size: 10pt;
										font-weight: bold;"><b style="font-weight: bold;"><span 
 style="font-weight: bold;"><B>FF Initial State -- </B></span><span style="font-weight: normal;">Sets 
 the initial state for all Flip-Flops. <!--kadov_tag{{<spaces>}}-->&nbsp;<!--kadov_tag{{</spaces>}}-->The 
 options are Low, High and FPGA.</span></b></p></li>
	
	<li class=kadov-p-Cwhs8><p class=whs8
								style="font-family: arial, sans-serif;
										font-size: 10pt;
										font-weight: bold;"><b><span style="font-weight: bold;"><B>Collapsing 
 P-Term Limit -- </B></span></b><span style="font-weight: normal;">This option 
 controls the degree to which the fitter flattens a design netlist. A logic 
 gate can collapse forward into a subsequent gate only if the number of 
 product terms in the resulting logic function does not exceed the p-term 
 limit. If the path delay of a logic function is not acceptable, increase 
 the p-term limit to allow the larger functions to be further flattened. 
 Choose a number from 3 to 48.</span> </p></li>
	
	<li class=kadov-p-Cwhs8><p class=whs8
								style="font-family: arial, sans-serif;
										font-size: 10pt;
										font-weight: bold;"><b><span style="font-weight: bold;"><B>Collapsing 
 Input Limit -- </B></span></b><span style="font-weight: normal;">This is a 
 secondary option for controlling the degree to which the fitter flattens 
 a design netlist. A logic gate can collapse forward into a subsequent 
 gate only if the number of inputs in the resulting logic function does 
 not exceed the input limit. If the design fails to fit the target device 
 because flattening uses up too many of the function block inputs, decrease 
 the input limit to prevent flattening of certain high fan-in functions. 
 </span><!--kadov_tag{{<spaces>}}-->&nbsp;<!--kadov_tag{{</spaces>}}--></p></li>
</ul>

<h2 class="whs19"><b><span 
 style="font-weight: bold;"><B><a name="XPLA Advanced Options"></a>XPLA Advanced 
 Options</B></span></b></h2>

<p class="whs20"><b><span style="font-weight: normal;">The 
 following options are available under XPLA </span><span style="font-weight: bold;"><B>Implementation 
 Options</B></span><span style="font-weight: normal;">, </span><span style="font-weight: bold;"><B>Advanced</B></span><span 
 style="font-weight: normal;"> tab.</span></b></p>

<ul>
	
	<li class=kadov-p-Cwhs8><p class=whs8
								style="font-family: arial, sans-serif;
										font-size: 10pt;
										font-weight: bold;">Enable Fast 
 Input Registers -<span style="font-weight: normal;">- Enables the use 
 of the Fast Input path in XPLA3 devices.</span></p></li>
	
	<li class=kadov-p-Cwhs8><p class=whs8
								style="font-family: arial, sans-serif;
										font-size: 10pt;
										font-weight: bold;">Enable Use 
 of Foldback NANDs -- <span style="font-weight: normal;">When selected, 
 the software will use foldback NANDs. This increases the capability to 
 fit a design, sometimes at the expense of speed.</span></p></li>
	
	<li class=kadov-p-Cwhs8><p class=whs8
								style="font-family: arial, sans-serif; font-size: 10pt;"><span 
 style="font-weight: bold;"><B>Reserve JTAG Pins for ISP -- </B></span>Checking 
 this box will instruct the fitter to reserve JTAG pins.</p></li>
</ul>

<h2 class="whs21"><a name="CoolRunner-II Advanced Options"></a>CoolRunner-II 
 Advanced Options</h2>

<p class="whs22">The following 
 options are found under the Advanced tab for CoolRunner-II devices.</p>

<ul type="disc" class="whs23">
	
	<li class=kadov-h4><h4 class="whs24">Use 
 Global Clock(s) -- <span style="font-weight: normal;">Select this option 
 to allow the fitter to assign input pins used as clocks to dedicated global 
 clock (GCK) pins of the device. If this option is disabled, only pins 
 identified with the BUFG=CLK property in the design (or UCF file) will 
 be assigned to GCK device pins. By default, this option is on.</span> 
 </h4></li>
	
	<li class=kadov-p><p class="whs25"><span 
 style="font-weight: bold;"><B>Use Global Output Enable(s)</B></span> -- Select 
 this option to allow the fitter to assign input pins used as output enable 
 control to dedicated global OE (GTS) pins of the device. If this option 
 is disabled, only pins identified with the BUFG=OE property in the design 
 (or UCF file) will be assigned to GTS device pins. By default, this option 
 is on. </p></li>
	
	<li class=kadov-p><p class="whs26"><span 
 style="font-weight: bold;"><B>Use Global Set/Reset</B></span> -- Select this 
 option to allow the fitter to assign input pins used as register asynchronous 
 reset or preset control to the dedicated global set/reset (GSR) pin of 
 the device. If this option is disabled, only a pin identified with the 
 BUFG=SR property in the design (or UCF file) will be assigned to the GSR 
 device pin. By default, this option is on.</p></li>
	
	<li class=kadov-p><p class="whs27"><span 
 style="font-weight: bold;"><B>Enable Fast Input Registers</B></span> -- Enables 
 fast input registers.</p></li>
	
	<li class=kadov-p><p class="whs28"><span 
 style="font-weight: bold;"><B>Ignore DATA_GATE Attributes</B></span> -- Data