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<?xml version="1.0" encoding="gb2312"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=gb2312"/><title>linux for ppc chapter 7                jacobw </title></head><body><center><h1>BBS 水木清华站∶精华区</h1></center><a name="top"></a>发信人:&nbsp;plato&nbsp;(纯真年代),&nbsp;信区:&nbsp;Embedded&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<br />标&nbsp;&nbsp;题:&nbsp;linux&nbsp;for&nbsp;ppc&nbsp;chapter&nbsp;7&nbsp;<br />发信站:&nbsp;BBS&nbsp;水木清华站&nbsp;(Wed&nbsp;May&nbsp;30&nbsp;23:13:13&nbsp;2001)&nbsp;<br />&nbsp;<br />Next&nbsp;Previous&nbsp;Contents&nbsp;<br />----------------------------------------------------------------------------&nbsp;<br />----&nbsp;<br />7.&nbsp;Boot&nbsp;Sequence&nbsp;<br />The&nbsp;Linux&nbsp;boot&nbsp;sequence&nbsp;is&nbsp;more&nbsp;complicated&nbsp;than&nbsp;your&nbsp;average&nbsp;embedded&nbsp;opera&nbsp;<br />ting&nbsp;system,&nbsp;and&nbsp;there&nbsp;are&nbsp;many&nbsp;more&nbsp;options&nbsp;for&nbsp;configuring&nbsp;things.&nbsp;In&nbsp;gene&nbsp;<br />ral,&nbsp;the&nbsp;boot&nbsp;sequence&nbsp;goes&nbsp;like&nbsp;this:&nbsp;<br />Processor&nbsp;comes&nbsp;out&nbsp;of&nbsp;reset&nbsp;and&nbsp;branches&nbsp;to&nbsp;the&nbsp;ROM&nbsp;startup&nbsp;code.&nbsp;<br />The&nbsp;ROM&nbsp;startup&nbsp;code&nbsp;initialises&nbsp;the&nbsp;CPU&nbsp;and&nbsp;memory&nbsp;controller,&nbsp;performing&nbsp;o&nbsp;<br />nly&nbsp;minimal&nbsp;initialisation&nbsp;of&nbsp;on-chip&nbsp;devices,&nbsp;such&nbsp;as&nbsp;the&nbsp;console&nbsp;serial&nbsp;po&nbsp;<br />rt&nbsp;(typically&nbsp;SMC1&nbsp;on&nbsp;8xx&nbsp;devices)&nbsp;to&nbsp;provide&nbsp;boot&nbsp;diagnostic&nbsp;messages.&nbsp;It&nbsp;a&nbsp;<br />lso&nbsp;sets&nbsp;up&nbsp;the&nbsp;memory&nbsp;map&nbsp;for&nbsp;the&nbsp;kernel&nbsp;to&nbsp;use&nbsp;in&nbsp;a&nbsp;format&nbsp;that&nbsp;is&nbsp;consist&nbsp;<br />ent&nbsp;across&nbsp;platforms,&nbsp;and&nbsp;then&nbsp;jumps&nbsp;to&nbsp;the&nbsp;boot&nbsp;loader.&nbsp;<br />The&nbsp;boot&nbsp;loader&nbsp;decompresses&nbsp;the&nbsp;kernel&nbsp;into&nbsp;RAM,&nbsp;and&nbsp;jumps&nbsp;to&nbsp;it.&nbsp;<br />The&nbsp;kernel&nbsp;sets&nbsp;up&nbsp;the&nbsp;caches,&nbsp;initialises&nbsp;each&nbsp;of&nbsp;the&nbsp;hardware&nbsp;devices&nbsp;via&nbsp;&nbsp;<br />the&nbsp;init&nbsp;function&nbsp;in&nbsp;each&nbsp;driver,&nbsp;mounts&nbsp;the&nbsp;root&nbsp;filesystem&nbsp;and&nbsp;execs&nbsp;the&nbsp;i&nbsp;<br />nit&nbsp;process,&nbsp;which&nbsp;is&nbsp;the&nbsp;ultimate&nbsp;parent&nbsp;of&nbsp;all&nbsp;user&nbsp;mode&nbsp;processes,&nbsp;typica&nbsp;<br />lly&nbsp;/sbin/init.&nbsp;<br />Executing&nbsp;the&nbsp;first&nbsp;program&nbsp;linked&nbsp;against&nbsp;the&nbsp;shared&nbsp;C&nbsp;runtime&nbsp;library&nbsp;(oft&nbsp;<br />en&nbsp;init)&nbsp;causes&nbsp;the&nbsp;shared&nbsp;runtime&nbsp;library&nbsp;to&nbsp;be&nbsp;loaded.&nbsp;<br />In&nbsp;a&nbsp;typical&nbsp;Linux&nbsp;system,&nbsp;init&nbsp;reads&nbsp;/etc/inittab&nbsp;to&nbsp;execute&nbsp;the&nbsp;appropriat&nbsp;<br />e&nbsp;run&nbsp;control&nbsp;script&nbsp;from&nbsp;/etc/rc.d,&nbsp;which&nbsp;execute&nbsp;the&nbsp;start&nbsp;scripts&nbsp;to&nbsp;init&nbsp;<br />ialise&nbsp;networking&nbsp;and&nbsp;other&nbsp;system&nbsp;services.&nbsp;<br />In&nbsp;minimal&nbsp;embedded&nbsp;systems,&nbsp;init&nbsp;is&nbsp;commonly&nbsp;replaced&nbsp;with&nbsp;a&nbsp;simple&nbsp;C&nbsp;progr&nbsp;<br />am&nbsp;or&nbsp;shell&nbsp;script&nbsp;to&nbsp;start&nbsp;the&nbsp;appropriate&nbsp;services&nbsp;and/or&nbsp;application&nbsp;prog&nbsp;<br />rams,&nbsp;since&nbsp;the&nbsp;conventional&nbsp;rc&nbsp;scripts&nbsp;are&nbsp;often&nbsp;overkill.&nbsp;<br />----------------------------------------------------------------------------&nbsp;<br />----&nbsp;<br />Next&nbsp;Previous&nbsp;Contents&nbsp;&nbsp;<br />&nbsp;<br />--&nbsp;<br />&nbsp;<br />※&nbsp;来源:·BBS&nbsp;水木清华站&nbsp;smth.org·[FROM:&nbsp;166.111.161.8]&nbsp;<br /><a href="00000006.htm">上一篇</a><a href="javascript:history.go(-1)">返回上一页</a><a href="index.htm">回到目录</a><a href="#top">回到页首</a><a href="00000008.htm">下一篇</a></h1></center><center><h1>BBS 水木清华站∶精华区</h1></center></body></html>
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