mtd/html/faq jffs2.xml,1.1,1.2

[Artem Bityuckiy]

Update of /home/cvs/mtd/html/faq
In directory phoenix.infradead.org:/tmp/cvs-serv14917

Modified Files:
	jffs2.xml 
Log Message:
One a question about cleanmarkers.


Index: jffs2.xml
===================================================================
RCS file: /home/cvs/mtd/html/faq/jffs2.xml,v
retrieving revision 1.1
retrieving revision 1.2
diff -u -r1.1 -r1.2
--- jffs2.xml	12 Mar 2005 13:48:22 -0000	1.1
+++ jffs2.xml	15 Mar 2005 14:37:39 -0000	1.2
@@ -64,7 +64,7 @@
 <p>For <b>NOR FLASH</b> there are no restrictions. For <b>NAND FLASH</b> 
 please read the <a href="nand.html">NAND FAQ</a> section.</p>
 
-<h4>How does JFFS2 handle a block going bad in NAND flash ?</h4>
+<h3>How does JFFS2 handle a block going bad in NAND flash ?</h4>
 <p>If an error occurs when writing to a page, JFFS2 will attempt recovery of the
 data.  If the block contains nodes that have already been written to flash, the
 block is refiled onto the list of blocks that are bad but still in use
@@ -82,5 +82,23 @@
 non-permanent failures due to over-programing or write-disturb errors.  A block
 erase clears these conditions.</p>
 
+<h3>What is cleanmarker and what it is used for ?</h3>
+<p>Cleanmarker is a special JFFS2 node which is written to the beginning of block
+just after it has been erased. On NOR flashes it is a special small JFFS2 node
+at the beginning of the block. On NAND flash it is places to the spare area of
+the first block.</p>
+<p>The main reason why cleanmarkers are used to be sure that the block erase
+operation was correctly completed. All 0xFF bytes in the block are not
+necessarily mean the block is ready to be utilized. For example, if
+an unclean reboot happened just at the end of the block erase cycle, the block
+might have an unstable bits, which are read as "1" one time and might be read as
+"0" next time.</p>
+</p>When preparing a flash partition for JFFS2, it is recommended to put
+cleanmarkers to the erased blocks. This might be done my means of "-j" option of
+the "flash_erase" and "flash_eraseall" MTD utilities. Otherwise, JFFS2 will
+re-erase the blocks which contain all 0xFF and have no cleanmarker and waste
+time.</p>
+
+
 	<INCLUDE file="../inc/footer.tmpl" />
 </PAGE>