📄 yaffs-rootfs-howto.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"><HTML><HEAD> <META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=iso-8859-1"> <TITLE></TITLE> <META NAME="GENERATOR" CONTENT="StarOffice/5.2 (Linux)"> <META NAME="AUTHOR" CONTENT=" "> <META NAME="CREATED" CONTENT="20021126;22092300"> <META NAME="CHANGEDBY" CONTENT=" "> <META NAME="CHANGED" CONTENT="20021126;22222800"></HEAD><BODY><H1>Brief HOWTO on incorporating yaffs as a root fs.</H1><H4>By N C Bane <nick@cecomputing.co.uk></H4><H3>Document status</H3><P>This document is very much work in progress. It has been edited bydifferent people with no attempt to keep a consistent style. Beautywill come with age.</P><H2>What is yaffs?</H2><P>Yaffs stands for Yet Another Flash Filing System.</P><P>It is a journaling filesystem designed to run on NAND flash withspecial reference to embedded systems.</P><P><BR><BR></P><H2>Why would I want to use it?</H2><P>NAND flash (SmartMedia cards are repackaged raw NAND chips) ischeap and has a fast erase time as compared with NOR flash.</P><P>The NAND physical interface is very simple.</P><P>The small size and low current requirements make it very suitablefor embedded systems.</P><P>However, NAND has its problems. These are mainly due to bad blockmanagement as blocks of memory can be bad when the device is shippedand further blocks can become unusable over time.</P><P>Power can die unpredictably in embedded systems leading to dataloss and possibly file system corruption.</P><P>This is where yaffs comes in; it handles bad blocks and usesformats which are resistant to corruption.</P><P><BR><BR></P><H2>What do I need to know?</H2><P>It is assumed that the reader has a development system with directaccess to NAND flash (ie not a CF/SmartMedia adaptor which).</P><P>The user should be familiar with building linux kernels andpatching build trees.</P><P>It is strongly suggested that you also read more about NAND flashon the Linux mtd site.</P><P><BR><BR></P><H3>Assumptions:</H3><P>You have already downloaded the yaffs sources from the cvs atAleph1.</P><P>You have mtd code that exposes NAND as an mtdblock device.</P><P><BR><BR></P><H3>Nand interface:</H3><P>For yaffs to function, it must be able to be the only code thatwrites to the oob area on the NAND device.</P><P>The existing NAND driver in kernel 2.4.19 assumes that it will dothe ecc/oob management for the host fs. For yaffs, this is quitewrong.</P><P>You can disable ecc/oob calculations either by hand patching themtd code to bypass ecc calculations or by merging the latest mtd cvs.</P><P>The patches at http://www.toby-churchill.org have done the latter.</P><P><BR><BR></P><H3>Including yaffs as a kernel fs:</H3><P>1) Create [linux]/fs/yaffs directory in your kernel test source.</P><P>2) Copy devextras.h yaffs_fs.c yaffs_gets.c yaffs_guts.hyaffs_mtdif.c yaffs_mtdif.h yaffsinterface.h and yportenv.h from theyaffs sources to that directory.</P><P>3) Copy the Makefile from either the yaffs sources(Makefile.kernel) or the Balloon download site below to[linux]/fs/yaffs/Makefile.</P><P>3) Modify [linux]/fs/Config.in to include the 3 lines</P><P><BR><BR></P><P STYLE="margin-left: 2cm; font-weight: medium"><FONT SIZE=3>i<FONT FACE="Courier, monospace">f[ "CONFIG_MTD_NAND" = "y" ]; then</FONT></FONT></P><P STYLE="margin-left: 2cm; font-weight: medium"><FONT FACE="Courier, monospace"><FONT SIZE=3> tristate "Yaffs filesystem on NAND" CONFIG_YAFFS_FS</FONT></FONT></P><P STYLE="margin-left: 2cm; font-weight: medium"><FONT FACE="Courier, monospace"><FONT SIZE=3>fi</FONT></FONT></P><P>4) Configure the kernel to include (not modules) all the mtd nandcode (incl nand_ecc and mtdblock device) and yaffs fs.</P><P><BR><BR></P><P>You should now be able to build a kernel with yaffs as a root fsusing the normal tools.</P><P><BR><BR></P><H3>Creating a bootable yaffs partition:</H3><P>You can</P><P>1) Create the partition by mounting it from a running linux os andcopying the data there. The mkyaffs utility in the yaffs sourcesimply erases a NAND mtdblock device without removing bad block data.</P><P>2) Make and download a filesystem image. The mkyaffsimage utilitythat came with the sources will create a YAFFS block list in a filefrom a root tree. This is a list of 512+16 byte blocks that need tobe placed (in any order) on a NAND device.</P><P>You will need to write code to copy these data blocks and add inthe block numbers in the oob areas.</P><P>Examples of a modified handhelds.org bootldr for the Balloon boardcan be found on the toby-churchill.org website.</P><P><BR><BR></P><H3>Booting into yaffs:</H3><P>Modify your bootloader to pass a command line to linux tospecifying the mtdblock/n that refers to the root partition.</P><P><BR><BR></P><H3>Further Information:</H3><P>Yaffs page at Aleph1http://www.aleph1.co.uk/armlinux/projects/yaffs/index.html</P><P>Balloon page at http://www.toby-churchill.org.uk</P><P>Yaffs mailing list - to join send an email toyaffs-request@toby-churchill.org with the text "subscribe"(no quotes) as the subject</P><P>Linux MTD http://www.linux-mtd.infradead.org/</P><P>$Id: yaffs-rootfs-howto.html,v 1.1 2002/11/26 09:32:08 charles Exp $</P><P><BR><BR></P></BODY></HTML>⌨️ 快捷键说明
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