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<h2>
<a name="1206868"> </a><font color="#003366" face="Verdana, Arial, Helvetica, sans-serif">8.7 Troubleshooting target connections</font>
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<p>
<a name="1206869"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">For the ST20JEI and ST Micro Connect the <font size=2 face=Courier><strong>target</strong></font> command provides the ability to set the clock speed of the JTAG interface. It is possible for the JTAG connection to run faster than the target hardware can cope with; this is signified by the messages:</font>
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<a name="1206870"> </a><font size=2 face=Courier><strong>target not responding<br></strong></font>
<a name="1206871"> </a><font size=2 face=Courier><strong>communication timed out<br></strong></font>
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<a name="1206875"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The clock speed of the JTAG interface is set by adding an assignment to the <font size=2 face=Courier><strong>tckdiv</strong></font> parameter in the target definition. The JTAG clock frequency is divided by this parameter, which takes powers of 2 ranging from 2<sup>0</sup> to 2<sup>22 </sup>(only lower values are sensible). A value other than a power of 2 is rounded up to the next power of 2. The default value is 1.</font>
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<a name="1206876"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">As an example the following target definition instructs the ST20JEI <font face="Verdana, Arial, Helvetica, sans-serif"><b>mytarget</b></font> to set its clock frequency to run at half the default speed:</font>
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<a name="1206877"> </a><font size=2 face=Courier><strong>target mytarget tap "jei_soc mytarget tckdiv=2" "reset;tp3"<br></strong></font>
<h3>
<a name="1206878"> </a><font color="#003366" face="Verdana, Arial, Helvetica, sans-serif">8.7.1 Parallel troubleshooting</font>
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<h5>
<a name="1206879"> </a><i><font color="#003366" face="Verdana, Arial, Helvetica, sans-serif">Error - "cannot connect to target..."</font></i>
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<p>
<a name="1206880"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">If <strong>st20run</strong> rejects a connection with a "<font size=2 face=Courier><strong>cannot connect to target...</strong></font>" message, this indicates that it cannot talk to the interface box at all.</font>
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<a name="1206881"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">Connection problems include:</font>
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<ul>
<p> <font size=2 face="Verdana, Arial, Helvetica, sans-serif"><li ><a name="1206882"> </a>no power to the interface,</font></p>
<p> <font size=2 face="Verdana, Arial, Helvetica, sans-serif"><li ><a name="1206883"> </a>a bad connection between the PC and the interface,</font></p>
<p> <font size=2 face="Verdana, Arial, Helvetica, sans-serif"><li ><a name="1206884"> </a>target not specified in configuration file,</font></p>
</ul>
<h5>
<a name="1206885"> </a><i><font color="#003366" face="Verdana, Arial, Helvetica, sans-serif">EPP mode gives no performance improvement</font></i>
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<p>
<a name="1206886"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">If there does not appear to be a significant performance advantage between using the parallel port driver in polled mode and interrupt driven EPP mode then the problem could be that the driver is defaulting to polled mode. It does this if it fails to detect an interrupt. This can be caused by another driver being installed that has already claimed the IRQ, or an incorrectly configured parallel port.</font>
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