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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 13               jacobw </title></head><body><center><h1>BBS 水木清華站∶精華區(qū)</h1></center><a name="top"></a>發(fā)信人:&nbsp;plato&nbsp;(純真年代),&nbsp;信區(qū):&nbsp;Embedded&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<br />標(biāo)&nbsp;&nbsp;題:&nbsp;linux&nbsp;for&nbsp;ppc&nbsp;chapter&nbsp;13&nbsp;<br />發(fā)信站:&nbsp;BBS&nbsp;水木清華站&nbsp;(Wed&nbsp;May&nbsp;30&nbsp;23:18:46&nbsp;2001)&nbsp;<br />&nbsp;<br />Next&nbsp;Previous&nbsp;Contents&nbsp;<br />----------------------------------------------------------------------------&nbsp;<br />----&nbsp;<br />13.&nbsp;Root&nbsp;Filesystem&nbsp;<br />You&nbsp;need&nbsp;a&nbsp;root&nbsp;filesystem&nbsp;for&nbsp;the&nbsp;to&nbsp;kernel&nbsp;mount&nbsp;at&nbsp;startup.&nbsp;There&nbsp;are&nbsp;man&nbsp;<br />y&nbsp;options,&nbsp;and&nbsp;the&nbsp;best&nbsp;one&nbsp;will&nbsp;generally&nbsp;depend&nbsp;on&nbsp;whether&nbsp;your&nbsp;system&nbsp;nee&nbsp;<br />ds&nbsp;to&nbsp;be&nbsp;able&nbsp;to&nbsp;store&nbsp;persistent&nbsp;data&nbsp;(which&nbsp;must&nbsp;survive&nbsp;power&nbsp;cycling)&nbsp;in&nbsp;<br />&nbsp;the&nbsp;field.&nbsp;<br />See:&nbsp;<a href="http://lists.linuxppc.org/listarcs/linuxppc-embedded/200003/msg00067.ht">http://lists.linuxppc.org/listarcs/linuxppc-embedded/200003/msg00067.ht</a>&nbsp;<br />ml.&nbsp;<br />Your&nbsp;best&nbsp;bet&nbsp;is&nbsp;likely&nbsp;to&nbsp;be&nbsp;the&nbsp;root&nbsp;filesystem&nbsp;from&nbsp;Hard&nbsp;Hat&nbsp;Linux.&nbsp;Extra&nbsp;<br />ct&nbsp;all&nbsp;the&nbsp;RPMs&nbsp;matching&nbsp;*.noarch.rpm,&nbsp;and&nbsp;use&nbsp;the&nbsp;image&nbsp;in&nbsp;opt/hardhat/devk&nbsp;<br />it/ppc/8xx/target&nbsp;as&nbsp;the&nbsp;root&nbsp;filesystem.&nbsp;<br />13.1&nbsp;NFS&nbsp;Mounted&nbsp;<br />During&nbsp;development,&nbsp;the&nbsp;embedded&nbsp;system&nbsp;can&nbsp;NFS-mount&nbsp;its&nbsp;root&nbsp;filesystem&nbsp;fr&nbsp;<br />om&nbsp;your&nbsp;file&nbsp;sever&nbsp;to&nbsp;provide&nbsp;a&nbsp;complete&nbsp;diskless&nbsp;Linux&nbsp;system.&nbsp;The&nbsp;file&nbsp;ser&nbsp;<br />ver&nbsp;need&nbsp;not&nbsp;be&nbsp;the&nbsp;same&nbsp;architecture&nbsp;as&nbsp;the&nbsp;embedded&nbsp;client.&nbsp;Answer&nbsp;&quot;Y&quot;&nbsp;to&nbsp;&nbsp;<br />the&nbsp;kernel&nbsp;configuration&nbsp;questions&nbsp;regarding&nbsp;NFS&nbsp;client&nbsp;and&nbsp;root&nbsp;filesystem&nbsp;&nbsp;<br />via&nbsp;NFS,&nbsp;and&nbsp;&quot;make&nbsp;zImage&quot;.&nbsp;The&nbsp;embedded&nbsp;system&nbsp;will&nbsp;attempt&nbsp;to&nbsp;mount&nbsp;its&nbsp;ro&nbsp;<br />ot&nbsp;filesystem&nbsp;from&nbsp;the&nbsp;server&nbsp;as&nbsp;&quot;/tftpboot/&lt;ipaddress&gt;&quot;,&nbsp;where&nbsp;&lt;ipaddress&gt;&nbsp;&nbsp;<br />is&nbsp;it's&nbsp;IP&nbsp;address.&nbsp;Install&nbsp;your&nbsp;root&nbsp;filesystem&nbsp;image&nbsp;in&nbsp;this&nbsp;directory&nbsp;as&nbsp;&nbsp;<br />root&nbsp;on&nbsp;the&nbsp;server,&nbsp;and&nbsp;export&nbsp;the&nbsp;directory&nbsp;tree&nbsp;with&nbsp;an&nbsp;entry&nbsp;in&nbsp;/etc/expo&nbsp;<br />rts&nbsp;on&nbsp;the&nbsp;server,&nbsp;like:&nbsp;<br />&nbsp;&nbsp;&nbsp;&nbsp;/tftpboot&nbsp;&nbsp;&nbsp;(rw,no_root_squash)&nbsp;<br />If&nbsp;your&nbsp;system&nbsp;has&nbsp;a&nbsp;hard&nbsp;disk,&nbsp;you&nbsp;can&nbsp;start&nbsp;by&nbsp;using&nbsp;NFS&nbsp;then&nbsp;build&nbsp;a&nbsp;root&nbsp;<br />&nbsp;file&nbsp;system&nbsp;on&nbsp;the&nbsp;disk&nbsp;and&nbsp;boot&nbsp;from&nbsp;that.&nbsp;<br />If&nbsp;your&nbsp;system&nbsp;has&nbsp;no&nbsp;ethernet,&nbsp;you&nbsp;may&nbsp;want&nbsp;to&nbsp;start&nbsp;developing&nbsp;on&nbsp;a&nbsp;board&nbsp;&nbsp;<br />that&nbsp;does.&nbsp;<br />13.2&nbsp;Initial&nbsp;Ramdisk:&nbsp;initrd&nbsp;<br />To&nbsp;make&nbsp;a&nbsp;diskless&nbsp;system&nbsp;standalone,&nbsp;you&nbsp;need&nbsp;an&nbsp;initial&nbsp;ramdisk&nbsp;image&nbsp;cont&nbsp;<br />aining&nbsp;an&nbsp;ext2&nbsp;filesystem&nbsp;to&nbsp;put&nbsp;in&nbsp;arch/ppc/mbxboot/ramdisk.image.gz.&nbsp;Then,&nbsp;<br />&nbsp;build&nbsp;with&nbsp;&quot;make&nbsp;zImage.initrd&quot;&nbsp;and&nbsp;the&nbsp;ramdisk&nbsp;image&nbsp;will&nbsp;be&nbsp;mounted&nbsp;as&nbsp;th&nbsp;<br />e&nbsp;root&nbsp;filesystem&nbsp;at&nbsp;startup.&nbsp;See&nbsp;Documentation/initrd.txt&nbsp;in&nbsp;the&nbsp;kernel&nbsp;sou&nbsp;<br />rce&nbsp;tree.&nbsp;<br />You&nbsp;need&nbsp;to&nbsp;select&nbsp;both&nbsp;CONFIG_BLK_DEV_RAM&nbsp;and&nbsp;CONFIG_BLK_DEV_INITRD&nbsp;to&nbsp;buil&nbsp;<br />d&nbsp;zImage.initrd.&nbsp;You&nbsp;also&nbsp;need&nbsp;a&nbsp;file&nbsp;in&nbsp;arch/ppc/mbxboot&nbsp;called&nbsp;ramdisk.ima&nbsp;<br />ge.gz.&nbsp;When&nbsp;you&nbsp;build&nbsp;zImage.initrd,&nbsp;the&nbsp;secondary&nbsp;boot&nbsp;loader&nbsp;is&nbsp;re-compile&nbsp;<br />d&nbsp;with&nbsp;INITRD_OFFSET&nbsp;and&nbsp;INITRD_SIZE&nbsp;set,&nbsp;which&nbsp;are&nbsp;used&nbsp;to&nbsp;locate&nbsp;the&nbsp;start&nbsp;<br />&nbsp;and&nbsp;end&nbsp;of&nbsp;the&nbsp;ramdisk.image.gz&nbsp;file&nbsp;in&nbsp;memory.&nbsp;The&nbsp;start&nbsp;and&nbsp;end&nbsp;are&nbsp;passe&nbsp;<br />d&nbsp;to&nbsp;the&nbsp;kernel&nbsp;in&nbsp;registers&nbsp;(r4/r5??),&nbsp;which&nbsp;it&nbsp;saves&nbsp;into&nbsp;the&nbsp;variables&nbsp;in&nbsp;<br />itrd_start&nbsp;and&nbsp;initrd_end.&nbsp;The&nbsp;secondary&nbsp;boot&nbsp;loader&nbsp;also&nbsp;changes&nbsp;the&nbsp;kernel&nbsp;<br />&nbsp;command&nbsp;line&nbsp;arguments&nbsp;so&nbsp;that&nbsp;root=/dev/ram&nbsp;instead&nbsp;of&nbsp;root=/dev/nfs.&nbsp;The&nbsp;&nbsp;<br />kernel&nbsp;does&nbsp;various&nbsp;things&nbsp;if&nbsp;initrd_start&nbsp;is&nbsp;non-zero,&nbsp;but&nbsp;the&nbsp;main&nbsp;one&nbsp;is&nbsp;&nbsp;<br />to&nbsp;decompress&nbsp;the&nbsp;ramdisk.image.gz&nbsp;data&nbsp;into&nbsp;ramdisk&nbsp;0,&nbsp;and&nbsp;because&nbsp;root=/de&nbsp;<br />v/ram,&nbsp;this&nbsp;is&nbsp;then&nbsp;mounted&nbsp;as&nbsp;the&nbsp;root&nbsp;filesystem.&nbsp;<br />If&nbsp;your&nbsp;ramdisk&nbsp;is&nbsp;larger&nbsp;than&nbsp;4&nbsp;MB,&nbsp;you&nbsp;will&nbsp;need&nbsp;to&nbsp;add&nbsp;ramdisk=xxxx&nbsp;to&nbsp;th&nbsp;<br />e&nbsp;kernel&nbsp;command&nbsp;line&nbsp;at&nbsp;boot&nbsp;time,&nbsp;or&nbsp;modify&nbsp;drivers/block/rd.c.&nbsp;<br />Beware&nbsp;that&nbsp;the&nbsp;CPU6&nbsp;workarounds&nbsp;in&nbsp;the&nbsp;MontaVista&nbsp;2.2.x&nbsp;kernel&nbsp;clobber&nbsp;the&nbsp;&nbsp;<br />kernel&nbsp;command&nbsp;line,&nbsp;and&nbsp;cause&nbsp;the&nbsp;initial&nbsp;ramdisk&nbsp;mount&nbsp;to&nbsp;fail.&nbsp;See&nbsp;the&nbsp;th&nbsp;<br />read&nbsp;at:&nbsp;<a href="http://lists.linuxppc.org/listarcs/linuxppc-embedded/200004/msg0010">http://lists.linuxppc.org/listarcs/linuxppc-embedded/200004/msg0010</a>&nbsp;<br />3.html&nbsp;<br />There&nbsp;are&nbsp;a&nbsp;number&nbsp;of&nbsp;ways&nbsp;to&nbsp;create&nbsp;your&nbsp;inital&nbsp;ramdisk&nbsp;image,&nbsp;described&nbsp;be&nbsp;<br />low.&nbsp;For&nbsp;more&nbsp;info&nbsp;on&nbsp;building&nbsp;a&nbsp;root&nbsp;filesystem,&nbsp;see&nbsp;the&nbsp;Bootdisk&nbsp;HOWTO&nbsp;at:&nbsp;<br />&nbsp;<a href="http://www.linux.org/docs/ldp/howto/Bootdisk-HOWTO/buildroot.html">http://www.linux.org/docs/ldp/howto/Bootdisk-HOWTO/buildroot.html</a>&nbsp;<br />Examples&nbsp;<br />An&nbsp;example&nbsp;ramdisk.image.gz&nbsp;is&nbsp;already&nbsp;included&nbsp;in&nbsp;the&nbsp;Hard&nbsp;Hat&nbsp;kit.&nbsp;<br />A&nbsp;simple&nbsp;ramdisk&nbsp;for&nbsp;use&nbsp;with&nbsp;ppcboot&nbsp;is&nbsp;available&nbsp;at&nbsp;the&nbsp;Denx&nbsp;ftp&nbsp;site.&nbsp;<br />Using&nbsp;a&nbsp;ramdisk&nbsp;<br />You&nbsp;can&nbsp;also&nbsp;create&nbsp;your&nbsp;own&nbsp;on&nbsp;your&nbsp;development&nbsp;machine&nbsp;in&nbsp;a&nbsp;filesystem&nbsp;on&nbsp;&nbsp;<br />/dev/ram.&nbsp;If&nbsp;your&nbsp;ramdisk&nbsp;is&nbsp;larger&nbsp;than&nbsp;4&nbsp;MB,&nbsp;you&nbsp;will&nbsp;need&nbsp;to&nbsp;increase&nbsp;the&nbsp;<br />&nbsp;default&nbsp;ramdisk&nbsp;size&nbsp;on&nbsp;your&nbsp;development&nbsp;machine&nbsp;accordingly.&nbsp;<br />LILO&nbsp;users&nbsp;can&nbsp;do&nbsp;this&nbsp;by&nbsp;adding&nbsp;the&nbsp;following&nbsp;line&nbsp;to&nbsp;the&nbsp;first&nbsp;section&nbsp;of&nbsp;&nbsp;<br />/etc/lilo.conf:&nbsp;<br />ramdisk=65536&nbsp;<br />There&nbsp;is&nbsp;no&nbsp;real&nbsp;harm&nbsp;in&nbsp;asking&nbsp;for&nbsp;an&nbsp;excessive&nbsp;size,&nbsp;as&nbsp;/dev/ram*&nbsp;only&nbsp;all&nbsp;<br />ocates&nbsp;pages&nbsp;it&nbsp;actually&nbsp;needs&nbsp;to&nbsp;the&nbsp;ramdisk.&nbsp;However,&nbsp;you&nbsp;should&nbsp;use&nbsp;the&nbsp;&quot;&nbsp;<br />blocks-count&quot;&nbsp;parameter&nbsp;to&nbsp;limit&nbsp;the&nbsp;filesystem&nbsp;size&nbsp;when&nbsp;you&nbsp;run&nbsp;mke2fs&nbsp;to&nbsp;&nbsp;<br />prevent&nbsp;it&nbsp;creating&nbsp;unnecessarily&nbsp;large&nbsp;filesystem&nbsp;structures.&nbsp;<br />Using&nbsp;the&nbsp;loop&nbsp;device&nbsp;<br />Another&nbsp;approach&nbsp;is&nbsp;to&nbsp;use&nbsp;the&nbsp;loop&nbsp;device&nbsp;on&nbsp;your&nbsp;Linux&nbsp;development&nbsp;host&nbsp;to&nbsp;<br />&nbsp;mount&nbsp;the&nbsp;ramdisk&nbsp;image&nbsp;as&nbsp;a&nbsp;local&nbsp;filesystem,&nbsp;and&nbsp;then&nbsp;copy&nbsp;the&nbsp;files&nbsp;you&nbsp;&nbsp;<br />require&nbsp;into&nbsp;it.&nbsp;To&nbsp;allow&nbsp;users&nbsp;to&nbsp;mount&nbsp;the&nbsp;ramdisk.image&nbsp;on&nbsp;/mnt/loop&nbsp;with&nbsp;<br />&nbsp;&quot;mount&nbsp;/mnt/loop&quot;,&nbsp;add&nbsp;this&nbsp;entry&nbsp;to&nbsp;your&nbsp;/etc/fstab:&nbsp;<br />/path/to/ramdisk.image&nbsp;&nbsp;/mnt/loop&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;auto&nbsp;&nbsp;&nbsp;&nbsp;user,noauto,rw,loop&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;0&nbsp;0&nbsp;<br />Note&nbsp;that&nbsp;the&nbsp;minix&nbsp;file&nbsp;system&nbsp;code&nbsp;in&nbsp;Linux&nbsp;is&nbsp;not&nbsp;endian-independant,&nbsp;so&nbsp;&nbsp;<br />you&nbsp;can't&nbsp;build&nbsp;a&nbsp;minix&nbsp;file&nbsp;system&nbsp;image&nbsp;on&nbsp;an&nbsp;x86&nbsp;machine&nbsp;and&nbsp;expect&nbsp;to&nbsp;re&nbsp;<br />ad&nbsp;it&nbsp;on&nbsp;a&nbsp;PowerPC&nbsp;machine.&nbsp;ext2&nbsp;does&nbsp;not&nbsp;suffer&nbsp;from&nbsp;this&nbsp;problem.&nbsp;<br />For&nbsp;more&nbsp;info,&nbsp;see&nbsp;the&nbsp;Loopback-Root-FS&nbsp;HOWTO&nbsp;at:&nbsp;<a href="http://linuxdoc.org/HOWTO/">http://linuxdoc.org/HOWTO/</a>&nbsp;<br />mini/Loopback-Root-FS-HOWTO.html&nbsp;<br />13.3&nbsp;ROMFS&nbsp;Flash&nbsp;Filesystem&nbsp;<br />Search&nbsp;for&nbsp;ROMFS.&nbsp;<br />13.4&nbsp;cramfs&nbsp;<br />The&nbsp;2.4&nbsp;kernel&nbsp;series&nbsp;has&nbsp;a&nbsp;compressed&nbsp;read-only&nbsp;filesystem&nbsp;(cramfs)&nbsp;aimed&nbsp;a&nbsp;<br />t&nbsp;embedded&nbsp;systems,&nbsp;which&nbsp;can&nbsp;be&nbsp;back-ported&nbsp;to&nbsp;2.2&nbsp;kernels.&nbsp;If&nbsp;you're&nbsp;cross&nbsp;<br />-&nbsp;developing,&nbsp;you&nbsp;need&nbsp;to&nbsp;modify&nbsp;<br />mkcramfs&nbsp;<br />to&nbsp;swap&nbsp;between&nbsp;little&nbsp;and&nbsp;big&nbsp;endian.&nbsp;<br />13.5&nbsp;ramfs&nbsp;<br />ramfs&nbsp;from&nbsp;the&nbsp;2.4&nbsp;kernel&nbsp;is&nbsp;a&nbsp;simple&nbsp;filesystem&nbsp;ideal&nbsp;for&nbsp;use&nbsp;in&nbsp;a&nbsp;ramdisk.&nbsp;<br />&nbsp;It&nbsp;can&nbsp;be&nbsp;used&nbsp;in&nbsp;combination&nbsp;with&nbsp;a&nbsp;cramfs&nbsp;read-only&nbsp;root&nbsp;filesystem,&nbsp;to&nbsp;m&nbsp;<br />ount&nbsp;writable&nbsp;filesystems&nbsp;on&nbsp;<br />/tmp&nbsp;<br />and&nbsp;<br />/var&nbsp;<br />,&nbsp;which&nbsp;typically&nbsp;need&nbsp;to&nbsp;be&nbsp;writable.&nbsp;This&nbsp;combination&nbsp;is&nbsp;ideal&nbsp;for&nbsp;systems&nbsp;<br />&nbsp;which&nbsp;don't&nbsp;require&nbsp;persistent&nbsp;storage.&nbsp;<br />13.6&nbsp;Journaling&nbsp;Flash&nbsp;FileSystem&nbsp;<br /><a href="http://www.developer.axis.com/software/jffs/">http://www.developer.axis.com/software/jffs/</a>&nbsp;<br />JFFS&nbsp;allows&nbsp;persistent&nbsp;storage,&nbsp;optimised&nbsp;for&nbsp;flash&nbsp;memories&nbsp;rather&nbsp;than&nbsp;blo&nbsp;<br />ck&nbsp;devices&nbsp;like&nbsp;hard&nbsp;disks.&nbsp;It&nbsp;is&nbsp;aimed&nbsp;at&nbsp;providing&nbsp;a&nbsp;crash/powerdown-safe&nbsp;&nbsp;<br />filesystem&nbsp;for&nbsp;disk-less&nbsp;embedded&nbsp;devices&nbsp;and&nbsp;is&nbsp;a&nbsp;better&nbsp;option&nbsp;than&nbsp;the&nbsp;cr&nbsp;<br />amfs/ramfs&nbsp;combination&nbsp;if&nbsp;your&nbsp;application&nbsp;requires&nbsp;persistent&nbsp;storage.&nbsp;You&nbsp;&nbsp;<br />use&nbsp;it&nbsp;with&nbsp;the&nbsp;Memory&nbsp;Technology&nbsp;Device&nbsp;subsystem.&nbsp;<br />----------------------------------------------------------------------------&nbsp;<br />----&nbsp;<br />Next&nbsp;Previous&nbsp;Contents&nbsp;&nbsp;<br />&nbsp;<br />--&nbsp;<br />&nbsp;<br />※&nbsp;來源:·BBS&nbsp;水木清華站&nbsp;smth.org·[FROM:&nbsp;166.111.161.8]&nbsp;<br /><a href="00000012.htm">上一篇</a><a href="javascript:history.go(-1)">返回上一頁</a><a href="index.htm">回到目錄</a><a href="#top">回到頁首</a><a href="00000014.htm">下一篇</a></h1></center><center><h1>BBS 水木清華站∶精華區(qū)</h1></center></body></html>
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