Changes between Initial Version and Version 1 of spread_spectrum_oscillator

10/21/2017 10:28:45 PM (9 months ago)



  • spread_spectrum_oscillator

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     2          <div id="wikipage" class="trac-content"><p>
     3</p><div class="wiki-toc">
     5  <li>
     6    <a href="#SpreadSpectrumOscillator">Spread Spectrum Oscillator</a>
     7  </li>
     11<h1 id="SpreadSpectrumOscillator">Spread Spectrum Oscillator</h1>
     13Most of the Gateworks Avila and Cambria family products support a 'spread spectrum' oscillator for the main CPU clock as a means of reducing Electro-Magnetic interference (EMI). 
     16When using this option the linux kernel needs to be re-compiled with a configuration option to adjust the clocks that depend on this oscillator:
     18<ul><li>IXP4XX_TIMER_FREQ defined in arch/arm/mach-ixp4xx/include/mach/timex.h
     19</li><li>IXP4XX_UART_XTAL defined in arch/arm/mach-ixp4xx/include/mach/platform.h
     21The frequencies defined should be reduced by 1% for the 2% down spread-spectrum oscillator used.
     24An kernel patch is attached to this page which allows you to select a kernel configuration to adjust the frequencies for a board with the spread-spectrum oscillator loaded.  Note that this is a compile-time change, there is no support for run-time detection and/or adjustment based on a kernel parameter.  Once this patch is applied you can select the option via:
     26<pre class="wiki">make kernel_menuconfig # select 'System Type' -&gt; 'Intel IXP4xx Implementation Options' -&gt; 'Adjust clocks for 2% Down Spread Spectrum source' (CONFIG_IXP4XX_SPREAD_SPECTRUM_CLK=y)
     28A patch for adjusting the system clock and UART clock can be found <a class="ext-link" href=""><span class="icon">​</span>here</a> but needs to be merged into the kernel of your choice manually.