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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>在MIPS上移植linux                      doot </title></head><body><center><h1>BBS 水木清华站∶精华区</h1></center><a name="top"></a>发信人:&nbsp;BBF&nbsp;(棒棒头~~冷酷到底),&nbsp;信区:&nbsp;Embedded&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<br />标&nbsp;&nbsp;题:&nbsp;Re:&nbsp;移植一个Linux要修改那些部分涉及到哪些文件?&nbsp;<br />发信站:&nbsp;BBS&nbsp;水木清华站&nbsp;(Mon&nbsp;Apr&nbsp;16&nbsp;20:35:51&nbsp;2001)&nbsp;<br />&nbsp;<br />贴一篇权当灌水，写的精彩，可惜是说MIPS&nbsp;porting的&nbsp;<br />Linux&nbsp;Porting&nbsp;Guide&nbsp;<br />By&nbsp;Rajesh&nbsp;Palani&nbsp;<br />Embedded&nbsp;Systems&nbsp;Programming&nbsp;<br />(02/26/01,&nbsp;07:50:40&nbsp;PM&nbsp;EDT)&nbsp;<br />Why&nbsp;pay&nbsp;someone&nbsp;to&nbsp;port&nbsp;Linux&nbsp;for&nbsp;you?&nbsp;Here's&nbsp;oneLinux&nbsp;how-to&nbsp;no&nbsp;embedded&nbsp;pr&nbsp;<br />ogrammer&nbsp;should&nbsp;miss.&nbsp;<br />Linux&nbsp;is&nbsp;gaining&nbsp;in&nbsp;popularity&nbsp;in&nbsp;embedded&nbsp;systems.&nbsp;Many&nbsp;commercial&nbsp;vendors&nbsp;&nbsp;<br />specialize&nbsp;in&nbsp;porting&nbsp;Linux&nbsp;to&nbsp;embedded&nbsp;systems.&nbsp;This&nbsp;article&nbsp;explains&nbsp;the&nbsp;w&nbsp;<br />ork&nbsp;involved&nbsp;in&nbsp;porting&nbsp;Linux&nbsp;to&nbsp;a&nbsp;specific&nbsp;embedded&nbsp;system&nbsp;and&nbsp;how&nbsp;it&nbsp;was&nbsp;d&nbsp;<br />one&nbsp;for&nbsp;one&nbsp;embedded&nbsp;system&nbsp;in&nbsp;particular.&nbsp;<br />Until&nbsp;now,&nbsp;most&nbsp;embedded&nbsp;operating&nbsp;systems&nbsp;have&nbsp;been&nbsp;proprietary.&nbsp;If&nbsp;a&nbsp;new&nbsp;p&nbsp;<br />rocessor&nbsp;was&nbsp;designed&nbsp;and&nbsp;developed&nbsp;by&nbsp;a&nbsp;semiconductor&nbsp;company,&nbsp;they&nbsp;had&nbsp;to&nbsp;&nbsp;<br />depend&nbsp;on&nbsp;an&nbsp;operating&nbsp;system&nbsp;company&nbsp;to&nbsp;port&nbsp;their&nbsp;operating&nbsp;system&nbsp;to&nbsp;the&nbsp;&nbsp;<br />new&nbsp;processor.&nbsp;The&nbsp;other&nbsp;issue&nbsp;was&nbsp;with&nbsp;the&nbsp;development&nbsp;tools&nbsp;(compiler,&nbsp;deb&nbsp;<br />ugger,&nbsp;simulator,&nbsp;and&nbsp;so&nbsp;on)&nbsp;for&nbsp;the&nbsp;given&nbsp;processor.&nbsp;Usually&nbsp;the&nbsp;operating&nbsp;&nbsp;<br />system&nbsp;company&nbsp;also&nbsp;provided&nbsp;these&nbsp;tools.&nbsp;In&nbsp;addition,&nbsp;the&nbsp;peripherals&nbsp;aroun&nbsp;<br />d&nbsp;the&nbsp;processor&nbsp;required&nbsp;drivers&nbsp;that&nbsp;had&nbsp;to&nbsp;be&nbsp;developed&nbsp;for&nbsp;the&nbsp;specific&nbsp;o&nbsp;<br />perating&nbsp;system.&nbsp;With&nbsp;the&nbsp;introduction&nbsp;of&nbsp;Linux&nbsp;into&nbsp;the&nbsp;embedded&nbsp;sphere,&nbsp;it&nbsp;<br />&nbsp;has&nbsp;become&nbsp;possible&nbsp;for&nbsp;the&nbsp;semiconductor&nbsp;company&nbsp;itself&nbsp;to&nbsp;port&nbsp;an&nbsp;operati&nbsp;<br />ng&nbsp;system&nbsp;to&nbsp;a&nbsp;new&nbsp;processor,&nbsp;since&nbsp;the&nbsp;source&nbsp;code&nbsp;for&nbsp;the&nbsp;Linux&nbsp;kernel&nbsp;is&nbsp;&nbsp;<br />available&nbsp;as&nbsp;open&nbsp;source.&nbsp;The&nbsp;GNU&nbsp;[1]&nbsp;project&nbsp;provides&nbsp;a&nbsp;wealth&nbsp;of&nbsp;developme&nbsp;<br />nt&nbsp;tools&nbsp;that&nbsp;support&nbsp;Linux&nbsp;and&nbsp;are&nbsp;also&nbsp;open&nbsp;source.&nbsp;In&nbsp;addition,&nbsp;many&nbsp;devi&nbsp;<br />ce&nbsp;drivers&nbsp;are&nbsp;available&nbsp;for&nbsp;Linux,&nbsp;which&nbsp;could&nbsp;be&nbsp;used&nbsp;directly&nbsp;or&nbsp;as&nbsp;a&nbsp;sta&nbsp;<br />rting&nbsp;point&nbsp;for&nbsp;your&nbsp;target&nbsp;devices.&nbsp;<br />Project&nbsp;specifics&nbsp;<br />In&nbsp;our&nbsp;example,&nbsp;the&nbsp;target&nbsp;platform&nbsp;(development&nbsp;board)&nbsp;to&nbsp;which&nbsp;we&nbsp;ported&nbsp;L&nbsp;<br />inux&nbsp;consisted&nbsp;of&nbsp;an&nbsp;ASIC&nbsp;(application-specific&nbsp;integrated&nbsp;circuit)&nbsp;for&nbsp;Wind&nbsp;<br />ows-based&nbsp;terminals&nbsp;(thin&nbsp;client)&nbsp;and&nbsp;Internet&nbsp;access&nbsp;terminals,&nbsp;a&nbsp;MIPS&nbsp;CPU,&nbsp;<br />&nbsp;and&nbsp;a&nbsp;CPU&nbsp;interface&nbsp;(North&nbsp;Bridge).&nbsp;In&nbsp;addition,&nbsp;the&nbsp;development&nbsp;board&nbsp;also&nbsp;<br />&nbsp;supported&nbsp;EDO&nbsp;DRAM,&nbsp;flash&nbsp;ROM,&nbsp;I2C&nbsp;RTC,&nbsp;I2C&nbsp;EEPROM,&nbsp;and&nbsp;I2C&nbsp;serial&nbsp;bus.&nbsp;The&nbsp;<br />&nbsp;high-level&nbsp;system&nbsp;block&nbsp;diagram&nbsp;is&nbsp;shown&nbsp;in&nbsp;Figure&nbsp;1.&nbsp;An&nbsp;architectural&nbsp;bloc&nbsp;<br />k&nbsp;diagram&nbsp;of&nbsp;the&nbsp;ASIC&nbsp;is&nbsp;shown&nbsp;in&nbsp;Figure&nbsp;2.&nbsp;A&nbsp;ramdisk&nbsp;(explained&nbsp;later&nbsp;in&nbsp;th&nbsp;<br />e&nbsp;article)&nbsp;served&nbsp;as&nbsp;the&nbsp;root&nbsp;file&nbsp;system.&nbsp;A&nbsp;ramdisk&nbsp;was&nbsp;used&nbsp;initially&nbsp;in&nbsp;o&nbsp;<br />rder&nbsp;to&nbsp;speed&nbsp;up&nbsp;the&nbsp;porting&nbsp;process.&nbsp;Though&nbsp;this&nbsp;article&nbsp;is&nbsp;based&nbsp;on&nbsp;Linux&nbsp;&nbsp;<br />on&nbsp;MIPS,&nbsp;the&nbsp;overall&nbsp;approach&nbsp;is&nbsp;not&nbsp;very&nbsp;different&nbsp;for&nbsp;other&nbsp;processors&nbsp;(AR&nbsp;<br />M,&nbsp;386,&nbsp;and&nbsp;so&nbsp;on).&nbsp;In&nbsp;addition,&nbsp;the&nbsp;article&nbsp;deals&nbsp;only&nbsp;with&nbsp;minimum&nbsp;kernel&nbsp;&nbsp;<br />functionality.&nbsp;<br />Figure&nbsp;1&nbsp;<br />Figure&nbsp;2&nbsp;<br />Cross-development&nbsp;tools&nbsp;were&nbsp;used&nbsp;for&nbsp;this&nbsp;project.&nbsp;The&nbsp;current&nbsp;development&nbsp;&nbsp;<br />was&nbsp;done&nbsp;on&nbsp;a&nbsp;PC&nbsp;running&nbsp;Red&nbsp;Hat&nbsp;Linux.&nbsp;The&nbsp;Linux&nbsp;VR&nbsp;Web&nbsp;site&nbsp;(see&nbsp;Reference&nbsp;<br />s)&nbsp;is&nbsp;a&nbsp;good&nbsp;starting&nbsp;point&nbsp;for&nbsp;cross-development&nbsp;tools&nbsp;and&nbsp;sources&nbsp;for&nbsp;Linu&nbsp;<br />x&nbsp;on&nbsp;MIPS.&nbsp;The&nbsp;following&nbsp;cross-development&nbsp;tools&nbsp;need&nbsp;to&nbsp;be&nbsp;downloaded&nbsp;and&nbsp;i&nbsp;<br />nstalled&nbsp;on&nbsp;the&nbsp;PC&nbsp;running&nbsp;Linux:&nbsp;cross-binutils-as,&nbsp;ld,&nbsp;and&nbsp;so&nbsp;on;&nbsp;C&nbsp;cross&nbsp;&nbsp;<br />compiler;&nbsp;and&nbsp;cross-development&nbsp;C&nbsp;libraries.&nbsp;The&nbsp;detailed&nbsp;steps&nbsp;for&nbsp;installa&nbsp;<br />tion&nbsp;are&nbsp;available&nbsp;along&nbsp;with&nbsp;the&nbsp;tools.&nbsp;<br />The&nbsp;kernel&nbsp;sources&nbsp;<br />The&nbsp;Linux&nbsp;kernel&nbsp;sources&nbsp;for&nbsp;MIPS&nbsp;can&nbsp;be&nbsp;downloaded&nbsp;from&nbsp;the&nbsp;Linux-VR&nbsp;site.&nbsp;&nbsp;<br />One&nbsp;of&nbsp;the&nbsp;most&nbsp;important&nbsp;steps&nbsp;in&nbsp;porting&nbsp;Linux&nbsp;to&nbsp;a&nbsp;new&nbsp;target&nbsp;platform&nbsp;is&nbsp;<br />&nbsp;to&nbsp;have&nbsp;a&nbsp;very&nbsp;clear&nbsp;understanding&nbsp;of&nbsp;how&nbsp;the&nbsp;kernel&nbsp;sources&nbsp;are&nbsp;organized.&nbsp;<br />&nbsp;The&nbsp;following&nbsp;directory&nbsp;structure&nbsp;is&nbsp;not&nbsp;complete&nbsp;and&nbsp;includes&nbsp;only&nbsp;parts&nbsp;t&nbsp;<br />hat&nbsp;are&nbsp;of&nbsp;interest&nbsp;to&nbsp;this&nbsp;article.&nbsp;The&nbsp;$(TOPDIR)&nbsp;[2]&nbsp;has&nbsp;the&nbsp;following&nbsp;sub&nbsp;<br />-directories:&nbsp;<br />arch-This&nbsp;subdirectory&nbsp;contains&nbsp;all&nbsp;of&nbsp;the&nbsp;architecture-specific&nbsp;code.&nbsp;For&nbsp;e&nbsp;<br />ach&nbsp;supported&nbsp;architecture&nbsp;(MIPS,&nbsp;ARM,&nbsp;386,&nbsp;and&nbsp;so&nbsp;on),&nbsp;there&nbsp;is&nbsp;a&nbsp;subdirect&nbsp;<br />ory&nbsp;under&nbsp;&quot;arch&quot;.&nbsp;Each&nbsp;supported&nbsp;architecture&nbsp;subdirectory&nbsp;has&nbsp;four&nbsp;major&nbsp;su&nbsp;<br />bdirectories:&nbsp;<br />kernel,&nbsp;which&nbsp;contains&nbsp;the&nbsp;architecture-specific&nbsp;kernel&nbsp;code&nbsp;<br />mm,&nbsp;which&nbsp;contains&nbsp;the&nbsp;architecture-specific&nbsp;memory&nbsp;management&nbsp;code&nbsp;<br />lib,&nbsp;which&nbsp;contains&nbsp;architecture&nbsp;specific&nbsp;library&nbsp;code&nbsp;(vsprintf&nbsp;and&nbsp;so&nbsp;on)&nbsp;<br />MY_PLATFORM&nbsp;(target&nbsp;platform&nbsp;directory),&nbsp;which&nbsp;contains&nbsp;platform-specific&nbsp;co&nbsp;<br />de.&nbsp;<br />Note&nbsp;that&nbsp;Linux&nbsp;ports&nbsp;to&nbsp;processors&nbsp;without&nbsp;memory&nbsp;management&nbsp;units&nbsp;(MMU)&nbsp;ar&nbsp;<br />e&nbsp;also&nbsp;available&nbsp;<br />documentation-This&nbsp;subdirectory&nbsp;contains&nbsp;the&nbsp;documentation&nbsp;for&nbsp;the&nbsp;kernel&nbsp;<br />drivers-This&nbsp;subdirectory&nbsp;contains&nbsp;code&nbsp;for&nbsp;the&nbsp;device&nbsp;drivers.&nbsp;Each&nbsp;type&nbsp;of&nbsp;<br />&nbsp;device&nbsp;has&nbsp;further&nbsp;subdirectories,&nbsp;such&nbsp;as&nbsp;char,&nbsp;block,&nbsp;net,&nbsp;and&nbsp;so&nbsp;on&nbsp;<br />fs-This&nbsp;directory&nbsp;contains&nbsp;the&nbsp;file&nbsp;system&nbsp;code.&nbsp;This&nbsp;has&nbsp;further&nbsp;sub-direct&nbsp;<br />ories&nbsp;for&nbsp;each&nbsp;supported&nbsp;file&nbsp;system&nbsp;(ext2,&nbsp;proc,&nbsp;and&nbsp;so&nbsp;on)&nbsp;<br />include-The&nbsp;include&nbsp;subdirectory&nbsp;contains&nbsp;the&nbsp;include&nbsp;files&nbsp;for&nbsp;the&nbsp;kernel.&nbsp;&nbsp;<br />It&nbsp;has&nbsp;further&nbsp;subdirectories&nbsp;for&nbsp;common&nbsp;include&nbsp;files&nbsp;(for&nbsp;all&nbsp;architecture&nbsp;<br />s),&nbsp;one&nbsp;for&nbsp;every&nbsp;architecture&nbsp;supported,&nbsp;and&nbsp;a&nbsp;couple&nbsp;of&nbsp;other&nbsp;subdirectori&nbsp;<br />es&nbsp;<br />init-This&nbsp;directory&nbsp;contains&nbsp;the&nbsp;initialization&nbsp;code&nbsp;for&nbsp;the&nbsp;kernel&nbsp;<br />kernel-This&nbsp;directory&nbsp;contains&nbsp;the&nbsp;main&nbsp;kernel&nbsp;code&nbsp;<br />lib-This&nbsp;directory&nbsp;contains&nbsp;the&nbsp;library&nbsp;code&nbsp;of&nbsp;the&nbsp;kernel&nbsp;<br />mm-This&nbsp;directory&nbsp;contains&nbsp;the&nbsp;memory&nbsp;management&nbsp;code&nbsp;<br />Building&nbsp;the&nbsp;kernel&nbsp;image&nbsp;<br />The&nbsp;Makefile&nbsp;in&nbsp;the&nbsp;$(TOPDIR)&nbsp;has&nbsp;to&nbsp;have&nbsp;ARCH&nbsp;(architecture)&nbsp;properly&nbsp;defin&nbsp;<br />ed&nbsp;(MIPS&nbsp;in&nbsp;this&nbsp;case).&nbsp;The&nbsp;Makefile&nbsp;in&nbsp;$(TOPDIR)/arch/MY_&nbsp;ARCH/boot&nbsp;has&nbsp;to&nbsp;&nbsp;<br />have&nbsp;CROSS_COMPILE&nbsp;(mipsel-linux,&nbsp;MIPS&nbsp;little-endian&nbsp;cross-compiler&nbsp;tool-set&nbsp;<br />&nbsp;in&nbsp;this&nbsp;case)&nbsp;and&nbsp;LOADADDR&nbsp;(address&nbsp;at&nbsp;which&nbsp;the&nbsp;kernel&nbsp;image&nbsp;would&nbsp;be&nbsp;load&nbsp;<br />ed)&nbsp;defined&nbsp;as&nbsp;per&nbsp;the&nbsp;configuration.&nbsp;If&nbsp;additional&nbsp;configuration&nbsp;options&nbsp;ha&nbsp;<br />ve&nbsp;to&nbsp;be&nbsp;added,&nbsp;the&nbsp;$(TOPDIR)/arch/MY_ARCH/config.in&nbsp;file&nbsp;has&nbsp;to&nbsp;be&nbsp;modified&nbsp;<br />.&nbsp;You&nbsp;would&nbsp;need&nbsp;to&nbsp;have&nbsp;a&nbsp;config&nbsp;option&nbsp;for&nbsp;your&nbsp;platform&nbsp;(CONFIG_MYPLATFOR&nbsp;<br />M)&nbsp;to&nbsp;include&nbsp;code&nbsp;that&nbsp;is&nbsp;specific&nbsp;to&nbsp;your&nbsp;platform.&nbsp;The&nbsp;kernel&nbsp;has&nbsp;to&nbsp;be&nbsp;c&nbsp;<br />onfigured&nbsp;(&quot;make&nbsp;config&quot;)&nbsp;to&nbsp;the&nbsp;barest&nbsp;minimum&nbsp;needs&nbsp;(serial&nbsp;driver,&nbsp;ramdis&nbsp;<br />k&nbsp;driver,&nbsp;ext2&nbsp;file&nbsp;system).&nbsp;Then&nbsp;do&nbsp;a&nbsp;&quot;make&nbsp;dep&quot;&nbsp;to&nbsp;set&nbsp;up&nbsp;the&nbsp;dependencies&nbsp;<br />&nbsp;and&nbsp;finally&nbsp;a&nbsp;&quot;make&nbsp;vmlinux&quot;&nbsp;to&nbsp;produce&nbsp;the&nbsp;kernel&nbsp;image.&nbsp;<br />Ramdisk&nbsp;<br />To&nbsp;begin&nbsp;with,&nbsp;a&nbsp;ramdisk&nbsp;can&nbsp;be&nbsp;mounted&nbsp;as&nbsp;the&nbsp;root&nbsp;file&nbsp;system.&nbsp;Ramdisk&nbsp;ima&nbsp;<br />ges&nbsp;and&nbsp;objects&nbsp;are&nbsp;also&nbsp;available&nbsp;readily&nbsp;for&nbsp;MIPS&nbsp;(Linux-VR&nbsp;site).&nbsp;A&nbsp;ramdi&nbsp;<br />sk&nbsp;image&nbsp;is&nbsp;a&nbsp;file&nbsp;that&nbsp;contains&nbsp;an&nbsp;image&nbsp;of&nbsp;an&nbsp;ext2&nbsp;filesystem,&nbsp;while&nbsp;a&nbsp;ram&nbsp;<br />disk&nbsp;object&nbsp;is&nbsp;an&nbsp;elf&nbsp;object&nbsp;that&nbsp;encapsulates&nbsp;a&nbsp;ramdisk&nbsp;image&nbsp;and&nbsp;can&nbsp;be&nbsp;li&nbsp;<br />nked&nbsp;into&nbsp;the&nbsp;kernel.&nbsp;The&nbsp;ramdisk&nbsp;image&nbsp;is&nbsp;usually&nbsp;stored&nbsp;in&nbsp;compressed&nbsp;form&nbsp;<br />.&nbsp;CONFIG_BLK_DEV_RAM&nbsp;and&nbsp;CONFIG_BLK_DEV_INITRD&nbsp;need&nbsp;to&nbsp;be&nbsp;defined&nbsp;as&nbsp;Y&nbsp;in&nbsp;&quot;m&nbsp;<br />ake&nbsp;config.&quot;&nbsp;The&nbsp;ramdisk&nbsp;image&nbsp;can&nbsp;be&nbsp;modified&nbsp;to&nbsp;include&nbsp;your&nbsp;applications,&nbsp;<br />&nbsp;if&nbsp;required.&nbsp;Tools&nbsp;(scripts)&nbsp;are&nbsp;available&nbsp;at&nbsp;the&nbsp;Linux&nbsp;VR&nbsp;site&nbsp;for&nbsp;creatin&nbsp;<br />g&nbsp;a&nbsp;ramdisk&nbsp;object.&nbsp;The&nbsp;ramdisk.o&nbsp;file&nbsp;needs&nbsp;to&nbsp;be&nbsp;copied&nbsp;to&nbsp;$(TOPDIR)/&nbsp;arch&nbsp;<br />/MY_ARCH/boot&nbsp;and&nbsp;linked&nbsp;into&nbsp;the&nbsp;kernel.&nbsp;There&nbsp;is&nbsp;a&nbsp;detailed&nbsp;document,&nbsp;$(TO&nbsp;<br />PDIR)/Documenta-tion/ramdisk.txt,&nbsp;on&nbsp;how&nbsp;to&nbsp;use&nbsp;the&nbsp;RAM&nbsp;disk&nbsp;block&nbsp;device&nbsp;wi&nbsp;<br />th&nbsp;Linux.&nbsp;<br />Processor-specific&nbsp;changes&nbsp;to&nbsp;the&nbsp;kernel&nbsp;code&nbsp;<br />If&nbsp;your&nbsp;processor&nbsp;is&nbsp;a&nbsp;standard&nbsp;(or&nbsp;popular)&nbsp;one,&nbsp;in&nbsp;most&nbsp;cases&nbsp;a&nbsp;Linux&nbsp;port&nbsp;<br />&nbsp;to&nbsp;that&nbsp;processor&nbsp;would&nbsp;be&nbsp;available.&nbsp;If&nbsp;you&nbsp;are&nbsp;one&nbsp;of&nbsp;the&nbsp;unlucky&nbsp;few&nbsp;who&nbsp;<br />&nbsp;has&nbsp;to&nbsp;deal&nbsp;with&nbsp;a&nbsp;specific&nbsp;implementation&nbsp;of&nbsp;a&nbsp;given&nbsp;processor&nbsp;core&nbsp;to&nbsp;whi&nbsp;<br />ch&nbsp;Linux&nbsp;has&nbsp;not&nbsp;yet&nbsp;been&nbsp;ported,&nbsp;you'll&nbsp;want&nbsp;to&nbsp;figure&nbsp;out&nbsp;which&nbsp;processor&nbsp;&nbsp;<br />in&nbsp;the&nbsp;list&nbsp;of&nbsp;ported&nbsp;ones&nbsp;is&nbsp;closest&nbsp;to&nbsp;yours&nbsp;and&nbsp;use&nbsp;that&nbsp;port&nbsp;as&nbsp;a&nbsp;starti&nbsp;<br />ng&nbsp;point&nbsp;for&nbsp;your&nbsp;specific&nbsp;processor&nbsp;implementation.&nbsp;For&nbsp;example,&nbsp;the&nbsp;MIPS&nbsp;c&nbsp;<br />ore&nbsp;is&nbsp;licensed&nbsp;to&nbsp;many&nbsp;silicon&nbsp;vendors&nbsp;who&nbsp;have&nbsp;their&nbsp;own&nbsp;implementations.&nbsp;&nbsp;<br />The&nbsp;number&nbsp;of&nbsp;TLB&nbsp;[3]&nbsp;(translation&nbsp;lookaside&nbsp;buffers)&nbsp;entries&nbsp;may&nbsp;be&nbsp;differe&nbsp;<br />nt&nbsp;for&nbsp;different&nbsp;implementations.&nbsp;Add&nbsp;a&nbsp;config&nbsp;option&nbsp;(CONFIG_MYCPU)&nbsp;to&nbsp;incl&nbsp;<br />ude&nbsp;code&nbsp;that&nbsp;is&nbsp;specific&nbsp;to&nbsp;your&nbsp;processor.&nbsp;Directories&nbsp;$(TOPDIR)/arch/MY_A&nbsp;<br />RCH/kernel&nbsp;and&nbsp;$(TOPDIR)/arch/MY_ARCH/mm&nbsp;contain&nbsp;the&nbsp;processor-specific&nbsp;code&nbsp;<br />&nbsp;that&nbsp;require&nbsp;modifications&nbsp;if&nbsp;you&nbsp;are&nbsp;dealing&nbsp;with&nbsp;a&nbsp;new&nbsp;implementation.&nbsp;<br />Assembly&nbsp;file&nbsp;$(TOPDIR)/arch/MY_ARCH/kernel/head.S&nbsp;contains&nbsp;kernel_entry,&nbsp;th&nbsp;<br />e&nbsp;entry&nbsp;point&nbsp;for&nbsp;the&nbsp;kernel.&nbsp;This&nbsp;file&nbsp;also&nbsp;contains&nbsp;the&nbsp;exception&nbsp;handling&nbsp;<br />&nbsp;code.&nbsp;Listing&nbsp;1&nbsp;shows&nbsp;the&nbsp;implementation&nbsp;of&nbsp;the&nbsp;kernel_entry&nbsp;routine&nbsp;in&nbsp;pse&nbsp;<br />udocode.&nbsp;<br />Listing&nbsp;1:&nbsp;Kernel&nbsp;entry&nbsp;pseudocode&nbsp;<br />1.&nbsp;&nbsp;Set&nbsp;desired&nbsp;endian&nbsp;mode&nbsp;<br />2.&nbsp;&nbsp;Clear&nbsp;the&nbsp;BEV&nbsp;bit&nbsp;<br />3.&nbsp;&nbsp;Set&nbsp;the&nbsp;TLB&nbsp;bit&nbsp;<br />4.&nbsp;&nbsp;GOTO&nbsp;cpu_probe&nbsp;and&nbsp;return&nbsp;<br />5.&nbsp;&nbsp;Set&nbsp;up&nbsp;stack&nbsp;for&nbsp;kernel&nbsp;<br />6.&nbsp;&nbsp;Clear&nbsp;bss&nbsp;<br />7.&nbsp;&nbsp;GOTO&nbsp;prom_init&nbsp;and&nbsp;return&nbsp;<br />8.&nbsp;&nbsp;GOTO&nbsp;loadmmu&nbsp;and&nbsp;return&nbsp;<br />9.&nbsp;&nbsp;Disable&nbsp;coprocessors&nbsp;<br />10.&nbsp;GOTO&nbsp;start_kernel&nbsp;<br />11.&nbsp;GOTO&nbsp;10&nbsp;<br />The&nbsp;configuration&nbsp;register&nbsp;has&nbsp;to&nbsp;be&nbsp;set&nbsp;up&nbsp;correctly.&nbsp;The&nbsp;first&nbsp;thing&nbsp;to&nbsp;be&nbsp;<br />&nbsp;done&nbsp;is&nbsp;to&nbsp;make&nbsp;sure&nbsp;that&nbsp;we&nbsp;are&nbsp;running&nbsp;in&nbsp;the&nbsp;desired&nbsp;endian&nbsp;mode.&nbsp;In&nbsp;our&nbsp;<br />&nbsp;case,&nbsp;we&nbsp;run&nbsp;the&nbsp;system&nbsp;in&nbsp;little-endian&nbsp;mode.&nbsp;The&nbsp;bootstrap&nbsp;exception&nbsp;vect&nbsp;<br />or&nbsp;bit&nbsp;needs&nbsp;to&nbsp;be&nbsp;cleared&nbsp;to&nbsp;make&nbsp;sure&nbsp;that&nbsp;the&nbsp;normal&nbsp;exception&nbsp;vectors&nbsp;ar&nbsp;<br />e&nbsp;used&nbsp;henceforth.&nbsp;In&nbsp;addition,&nbsp;the&nbsp;TLB&nbsp;bit&nbsp;is&nbsp;set&nbsp;to&nbsp;make&nbsp;sure&nbsp;that&nbsp;TLB-bas&nbsp;<br />ed&nbsp;translation&nbsp;is&nbsp;used.&nbsp;<br />The&nbsp;next&nbsp;step&nbsp;is&nbsp;to&nbsp;probe&nbsp;for&nbsp;the&nbsp;cputype.&nbsp;Listing&nbsp;2&nbsp;is&nbsp;a&nbsp;very&nbsp;simple&nbsp;implem&nbsp;<br />
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