ShuriZma
/
pcsx2
mirror of https://github.com/PCSX2/pcsx2.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity
pcsx2/pcsx2/Reference/PS2-MemoryCardFileSystem.htm

883 lines
32 KiB
HTML
Raw Blame History

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

<html><head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>
PlayStation 2 Memory Card File System
</title>
</head>
<body>
<h1>
PlayStation 2 Memory Card File System
</h1>
<div style="clear: both">
<h2>By
<a href="https://plus.google.com/101505960668383360394/?rel=author">
Ross Ridge
</a>
</h2>
<h2>Public Domain</h2>
</div>
<div style="clear: both">
<p>
This document is a description of the file system layout as used on
PlayStation 2 memory cards. It's based on the research I did while
writing <a href="http://www.csclub.uwaterloo.ca/%7Erridge/mymc">mymc</a>,
a utility for working with PS2 memory card images. This document
tries to be comprehensive an accurate, but some details may be
missing, misleading or just plain wrong. At lot of assumptions had to
be made during my research, and it's hard know to what exactly Sony
intended in every case. All most all of the names for structures,
fields and flags were made up by me. Nothing in this document should
be considered official.
</p>
<p>
For brevity, unused fields and flag bits are omitted from the tables.
In most cases unused fields or flags should be assumed to be either
reserved or padding and set to zero when writing. In particular,
you'll need to pad out the structures to the length given at the top
of the table. All values are stored on the card using the
little-endian byte order.
</p>
</div>
<div style="clear: both">
<h2>NAND Flash Memory Basics</h2>
<div style="float: right; padding: 1em 0 1em 1em; width: 40%">
<h3>Glossary</h3>
<p>A number of terms are used in this document that you may not
familiar with or are different from other sources describing PS2
memory cards, so I've created short glossary.
</p>
<dl>
<dt>block</dt>
<dd>See "erase block".</dd>
<dt>cluster</dt>
<dd>The unit of allocation used in the file system. A cluster
is one or more pages in size.</dd>
<dt>ECC</dt>
<dd>Error correcting code. A means of encoding data so that random
bit errors can be detected and corrected.</dd>
<dt>erase block</dt>
<dd>The basic erasable unit on a memory card.</dd>
<dt><code style="font-family: monospace">half</code></dt>
<dd>A two byte unsigned half-word value.</dd>
<dt>page</dt>
<dd>The basic addressable unit on a memory card. Corresponds to page
on the flash device used in the memory card, and is analogous
to a sector on hard disk.</dd>
<dt>programming</dt>
<dd>The operation of changing erased bits on a flash device from 1 to 0.</dd>
<dt>superblock</dt>
<dd>The first page on the memory card where important information
about the structure of the file system is kept.</dd>
<dt><code style="font-family: monospace">word</code></dt>
<dd>A four byte unsigned word value.</dd>
</dl>
</div>
<p>Since PlayStation 2 (PS2) memory cards use NAND Flash it's helpful to
understand some of the basics about this kind of memory works.
Flash is a non-volatile form of memory that can be electrically
erased and reprogrammed. Since it's non-volatile, meaning it
doesn't need power to retain data, and reprogramable, meaning the
data stored can be changed, it's the ideal form memory to use in
memory card. However, flash memory does have number of limitations
which affect how the PS2 uses its memory cards.
</p>
<p>One of the limitations is a relatively slow random access time.
While much faster than hard disk, NAND flash is much slower than
RAM at reading random bytes in memory. Reading the first byte of
data from a flash device takes about 25 microseconds. Fortunately,
reading on sequentially is much faster. After the first
byte is read, each subsequent byte takes only about 50 nanoseconds
to read. For this reason NAND flash memory is organized in to pages,
similar to how a hard drive is organized into sectors.
For example, with the TC58V64AFT, a flash device used in PS2 memory cards,
an entire 528 byte page can be read at a sustained 10 Mb/s
transfer rate. By comparison, the transfer rate for reading random
bytes is much slower, only 40kb/s. <em>Because the serial bus the
PS2 uses to talk to memory cards isn't capable of 10 Mb/s, actual
transfer rates will be slower.</em>
</p>
<p>The biggest limitation of flash devices is how they're written.
Instead changing bits of memory to 0 or 1 depending on the data
being written, flash memory can only change a bit from 1 to 0.
Once a bit of memory has been changed to 0, it can't be changed
back to 1 except by erasing it. Erasing is an operation that sets
an entire range of memory, called an erase block, to all 1s. Once
a block is erased, it can be written through an operation called
programming which changes 1 bits to 0 bits. Since an erase block
is made up of a number of pages, this makes writing a more
complicated operation than it would be on a hard disk. In order to
write a single page to a flash device you need to erase to the
block that the page belongs to. However, since that will erase all
the pages that belong to that block, not just the page being
written, you first need to read in all of the other pages that are
going to be erased. After the block is erased you then can program
the erase block with the contents of the page you're trying to
write and along with the content of all the other pages.
<em>Some flash devices work the other way, erasing sets the block
to all 0s while programming changes 0s to 1s.</em>
</p>
<p>Another limitation is that flash memory isn't as reliable as RAM
memory. A flash device will typically have a certain number of bad
blocks when it ships from the factory, and it's possible for
defects to appear in the media as it used. Also, a block can
eventually "wear out" after a few hundred thousand program/erase
cycles. For this reason each page is divided into two parts, a
data area a spare area. The data area is used to store ordinary
data, while the much smaller spare area is for software defined
error-correcting codes (ECC), wear leveling, bad block remapping,
and other functions meant to deal with defects in the media.
</p>
<p>The flash devices used in PS2 memory cards have a 528 byte page
size. This is divided into a 512 byte data area and 16 byte spare
area. The spare area is used to store 12 bytes of ECC data, with
the remaining 4 bytes left unused. Erase blocks are 16 pages long.
The are 16384 pages, for a total combined raw data area capacity
8,388,608 bytes.
</p>
</div>
<div style="clear: both">
<h2>File System Organization</h2>
<div style="float: right; padding: 1em 0 1em 1em">
<h3>Standard Memory<br>
Card Layout</h3>
<table>
<colgroup></colgroup>
<colgroup align="center" valign="middle"></colgroup>
<tbody><tr valign="top">
<td><code>0x0000</code></td>
<td rowspan="1" style="border: black solid thin" valign="middle">Superblock</td>
</tr>
<tr valign="top">
<td><code>0x0001</code></td>
<td rowspan="2" style="border: black solid thin" valign="middle">Unused</td>
</tr>
<tr><td>&nbsp;</td></tr>
<tr valign="top">
<td><code>0x0010</code></td>
<td rowspan="1" style="border: black solid thin" valign="middle">Indirect FAT Table</td>
</tr>
<tr valign="top">
<td><code>0x0012</code></td>
<td rowspan="4" style="border: black solid thin" valign="middle">FAT Table</td>
</tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr valign="top">
<td><code>0x0052</code></td>
<td rowspan="20" style="border: black solid thin" valign="middle">Allocatable Clusters</td>
</tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr valign="top">
<td><code>0x3ED2</code></td>
<td rowspan="6" style="border: black solid thin" valign="middle">Reserved Clusters</td>
</tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td>&nbsp;</td></tr>
<tr valign="top">
<td><code>0x3FE0</code></td>
<td rowspan="2" style="border: black solid thin" valign="middle">Backup Block 2</td>
</tr>
<tr><td>&nbsp;</td></tr>
<tr valign="top">
<td><code>0x3FF0</code></td>
<td rowspan="2" style="border: black solid thin" valign="middle">Backup Block 1</td>
</tr>
<tr valign="bottom">
<td><code>0x3FFF</code></td>
</tr>
</tbody></table>
</div>
<p>The PS2 memory card file system has a fairly simple design, with
some allowances made for the limitations of flash memory. Its
overall structure is similar to the well known MS-DOS FAT file
system. It uses a file allocation table (FAT) to keep track of
allocated space and a hierarchical directory system where all of
a file's metadata is stored in its directory entry. Like the FAT file
system, which groups disk sectors into clusters, the PS2 memory
card file system groups flash memory pages in to clusters. On
standard PS2 memory cards, the cluster size 1024 bytes, or 2 pages
long.
</p>
<div>
<h3>The Superblock</h3>
<p>The key to the PS2 memory card file system is the superblock.
Located in the first page of the memory, this is the only part of
the file system with a fixed location. <em>While some things like
the do end up in fixed locations on standard 8M memory cards, you
shouldn't rely on this.</em>
</p>
<table rules="all">
<caption>Superblock (340 bytes)</caption>
<colgroup span="4" valign="top"></colgroup>
<colgroup span="1" valign="top"></colgroup>
<tbody><tr><th>Offset</th><th>Name</th><th>Type</th><th>Default</th>
<th>Description</th></tr>
<tr>
<td nowrap="nowrap"><code>0x00</code></td>
<td nowrap="nowrap"><code>magic</code></td>
<td nowrap="nowrap"><code>byte[28]</code></td>
<td nowrap="nowrap"><code>-</code></td>
<td>Identifies the card as being formatted.
Set to the ASCII string "<code style="font-family: monospace">Sony PS2 Memory Card Format </code>".
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x1C</code></td>
<td nowrap="nowrap"><code>version</code></td>
<td nowrap="nowrap"><code>byte[12]</code></td>
<td nowrap="nowrap"><code>1.X.0.0</code></td>
<td>Version number of the format used.
<br><em>Version 1.2 indicates full support for <code style="font-family: monospace">bad_block_list</code>.
</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x28</code></td>
<td nowrap="nowrap"><code>page_len</code></td>
<td nowrap="nowrap"><code>half</code></td>
<td nowrap="nowrap"><code>512</code></td>
<td>Size in bytes of a memory card page.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x2A</code></td>
<td nowrap="nowrap"><code>pages_per_cluster</code></td>
<td nowrap="nowrap"><code>half</code></td>
<td nowrap="nowrap"><code>2</code></td>
<td>The number of pages in a cluster.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x2C</code></td>
<td nowrap="nowrap"><code>pages_per_block</code></td>
<td nowrap="nowrap"><code>half</code></td>
<td nowrap="nowrap"><code>16</code></td>
<td>The number of pages in an erase block.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x2E</code></td>
<td nowrap="nowrap"><code>-</code></td>
<td nowrap="nowrap"><code>half</code></td>
<td nowrap="nowrap"><code>0xFF00</code></td>
<td><em>Doesn't seem to be used</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x30</code></td>
<td nowrap="nowrap"><code>clusters_per_card</code></td>
<td nowrap="nowrap"><code>word</code></td>
<td nowrap="nowrap"><code>8192</code></td>
<td>The total size of the card in clusters.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x34</code></td>
<td nowrap="nowrap"><code>alloc_offset</code></td>
<td nowrap="nowrap"><code>word</code></td>
<td nowrap="nowrap"><code>41</code></td>
<td>Cluster offset of the first allocatable cluster. Cluster values
in the FAT and directory entries are relative to this.
<br><em>This is the cluster immediately after the FAT</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x38</code></td>
<td nowrap="nowrap"><code>alloc_end</code></td>
<td nowrap="nowrap"><code>word</code></td>
<td nowrap="nowrap"><code>8135</code></td>
<td>The cluster after the highest allocatable cluster. Relative to
<code style="font-family: monospace">alloc_offset</code>.
<br><em>Not used.</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x3C</code></td>
<td nowrap="nowrap"><code>rootdir_cluster</code></td>
<td nowrap="nowrap"><code>word</code></td>
<td nowrap="nowrap"><code>0</code></td>
<td>First cluster of the root directory. Relative to
<code style="font-family: monospace">alloc_offset</code>.
<br><em>Must be zero.</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x40</code></td>
<td nowrap="nowrap"><code>backup_block1</code></td>
<td nowrap="nowrap"><code>word</code></td>
<td nowrap="nowrap"><code>1023</code></td>
<td>Erase block used as a backup area during programming.
<br><em>Normally the the last block on the card, it may have a different value
if that block was found to be bad.</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x44</code></td>
<td nowrap="nowrap"><code>backup_block2</code></td>
<td nowrap="nowrap"><code>word</code></td>
<td nowrap="nowrap"><code>1022</code></td>
<td>This block should be erased to all ones.
<br><em>Normally the the second last block on the card.</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x50</code></td>
<td nowrap="nowrap"><code>ifc_list</code></td>
<td nowrap="nowrap"><code>word[32]</code></td>
<td nowrap="nowrap"><code>8</code></td>
<td>List of indirect FAT clusters.
<br><em>On a standard 8M card there's only one indirect FAT cluster.</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0xD0</code></td>
<td nowrap="nowrap"><code>bad_block_list</code></td>
<td nowrap="nowrap"><code>word[32]</code></td>
<td nowrap="nowrap"><code>-1</code></td>
<td>List of erase blocks that have errors and shouldn't be used.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x150</code></td>
<td nowrap="nowrap"><code>card_type</code></td>
<td nowrap="nowrap"><code>byte</code></td>
<td nowrap="nowrap"><code>2</code></td>
<td>Memory card type.
<br><em>Must be 2, indicating that this is a PS2 memory card.</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x151</code></td>
<td nowrap="nowrap"><code>card_flags</code></td>
<td nowrap="nowrap"><code>byte</code></td>
<td nowrap="nowrap"><code>0x52</code></td>
<td>Physical characteristics of the memory card.
<br></td>
</tr>
</tbody></table>
<div style="float: right; padding: 1em 0 1em 1em; width: 40%">
<table rules="all">
<caption>Card Flags</caption>
<colgroup span="2" valign="top"></colgroup>
<colgroup span="1" valign="top"></colgroup>
<tbody><tr><th>Mask</th><th>Name</th><th>Description</th></tr>
<tr>
<td nowrap="nowrap"><code>0x01</code></td>
<td nowrap="nowrap"><code>CF_USE_ECC</code></td>
<td>Card supports ECC.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x08</code></td>
<td nowrap="nowrap"><code>CF_BAD_BLOCK</code></td>
<td>Card may have bad blocks.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x10</code></td>
<td nowrap="nowrap"><code>CF_ERASE_ZEROES</code></td>
<td>Erased blocks have all bits set to zero.
<br></td>
</tr>
</tbody></table>
</div>
<p>Most of the fields in the superblock should be self-explanatory.
The fields <code style="font-family: monospace">page_len</code>, <code style="font-family: monospace">pages_per_cluster</code>,
<code style="font-family: monospace">pages_per_block,</code> and <code style="font-family: monospace">clusters_per_card</code> define the
basic geometry of the file system. The FAT can be accessed using
<code style="font-family: monospace">ifc_list</code> and <code style="font-family: monospace">rootdir_cluster</code> gives the first cluster
of the root directory. Cluster offsets in FAT and directory
entries are all relative to <code style="font-family: monospace">alloc_offset</code>
</p>
<p>File systems ment to be compatible with the PS2's memory card
drivers have a fairly restricted set of geometry options. The
field <code style="font-family: monospace">page_size</code> can be either 512 or 1024. If the page size
is 512 then <code style="font-family: monospace">pages_per_cluster</code> can either be 1 or 2,
otherwise it can only be 1. The limit on <code style="font-family: monospace">pages_per_block</code> is
16. There doesn't seem to be any upper limit on
<code style="font-family: monospace">clusters_per_card</code>, however because of the size of <code style="font-family: monospace">ifc_list</code>
there can be no more than 8,388,608 allocatable clusters.
While the clusters the make up the FAT can be located anywhere, the
value of <code style="font-family: monospace">rootdir_cluster</code> must be 0, indicating that the first
allocatable cluster is the first cluster of the root directory.
</p>
</div>
<div>
<h3>File Allocation Table</h3>
<p>The file allocation table is used for keeping track of which
clusters are in use and form a linked-list of the clusters that
belong to each file. Each entry in the table is a 32-bit value.
If the the cluster corresponding to the entry is free then the most
significant bit will be clear. Otherwise, it will be set and the
lower 31-bits of the value are the index of the next cluster in the
file. These indexes are relative to <code style="font-family: monospace">alloc_offset</code> given in
the superblock. A value of <code style="font-family: monospace">0xFFFFFFFF</code> indicates that this
entry is the last cluster in the file.
</p>
<p>Unlike the MS-DOS FAT file system, the table isn't required to to
be in single contiguous range of clusters. Instead a system of
double-indirect indexing is used that allows the clusters that make
up the file allocation table to be scattered across file system.
The <code style="font-family: monospace">ifc_list</code> in the superblock contains a table 32-bit
cluster indexes (relative to the start of the card). The entries
in the <code style="font-family: monospace">ifc_list</code> point to the clusters that make up the
indirect table. The indirect table is also a table 32-bit cluster
indexes and these indexes point to the clusters that make up the
file allocation table.
</p>
<p>So assuming a cluster size of 1024, code to access an entry in the
FAT might look something like this:
</p>
<p style="margin-left: 4em"><code style="font-family: monospace">
fat_offset = fat_index % 256
<br>
indirect_index = fat_index / 256
<br>
indirect_offset = indirect_index % 256
<br>
dbl_indirect_index = indirect_index / 256
<br>
indirect_cluster_num = superblock.ifc_table[dbl_indirect_index]
<br>
indirect_cluster = read_cluster(indirect_cluster_num)
<br>
fat_cluster_num = indirect_cluster[indirect_offset]
<br>
fat_cluster = read_cluster(fat_cluster_num)
<br>
entry = fat_cluster[fat_offset]
</code></p>
</div>
<div>
<h3>Directories</h3>
<p>Directories are for the most part like regular files, except that they
contain directory entries rather than data. The root directory is
as its name suggests, the root of the card's hierarchical directory
structure. The first cluster of the root directory is given in the
<code style="font-family: monospace">rootdir_cluster</code> field of the superblock, and subsequent clusters
(if any) can be found by following chain of linked clusters in the FAT.
</p>
<div style="float: right; padding: 1em 0 1em 1em; width: 50%">
<table rules="all">
<caption>Directory Entry Mode Flags</caption>
<colgroup span="2" valign="top"></colgroup>
<colgroup span="1" valign="top"></colgroup>
<tbody><tr><th>Mask</th><th>Name</th><th>Description</th></tr>
<tr>
<td nowrap="nowrap"><code>0x0001</code></td>
<td nowrap="nowrap"><code>DF_READ</code></td>
<td>Read permission.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x0002</code></td>
<td nowrap="nowrap"><code>DF_WRITE</code></td>
<td>Write permission.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x0004</code></td>
<td nowrap="nowrap"><code>DF_EXECUTE</code></td>
<td>Execute permission.
<br><em>Unused</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x0008</code></td>
<td nowrap="nowrap"><code>DF_PROTECTED</code></td>
<td>Directory is copy protected.
<br><em>Meaningful only to the browser.</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x0010</code></td>
<td nowrap="nowrap"><code>DF_FILE</code></td>
<td>Regular file.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x0020</code></td>
<td nowrap="nowrap"><code>DF_DIRECTORY</code></td>
<td>Directory.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x0040</code></td>
<td nowrap="nowrap"><code>-</code></td>
<td><em>Used internally to create directories.</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x0080</code></td>
<td nowrap="nowrap"><code>-</code></td>
<td><em>Copied?</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x0100</code></td>
<td nowrap="nowrap"><code>-</code></td>
<td>-<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x0200</code></td>
<td nowrap="nowrap"><code>O_CREAT</code></td>
<td><em>Used to create files.</em></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x0400</code></td>
<td nowrap="nowrap"><code>DF_0400</code></td>
<td>Set when files and directories are created,
otherwise ignored.<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x0800</code></td>
<td nowrap="nowrap"><code>DF_POCKETSTN</code></td>
<td>PocketStation application save file.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x1000</code></td>
<td nowrap="nowrap"><code>DF_PSX</code></td>
<td>PlayStation save file.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x2000</code></td>
<td nowrap="nowrap"><code>DF_HIDDEN</code></td>
<td>File is hidden.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x4000</code></td>
<td nowrap="nowrap"><code>-</code></td>
<td>-<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x8000</code></td>
<td nowrap="nowrap"><code>DF_EXISTS</code></td>
<td>This entry is in use.
If this flag is clear, then the file or directory has been deleted.
<br></td>
</tr>
</tbody></table>
</div>
<table rules="all">
<caption>Directory Entry (512 bytes)</caption>
<colgroup span="3" valign="top"></colgroup>
<colgroup span="1" valign="top"></colgroup>
<tbody><tr><th>Offset</th><th>Name</th><th>Type</th><th>Description</th></tr>
<tr>
<td nowrap="nowrap"><code>0x00</code></td>
<td nowrap="nowrap"><code>mode</code></td>
<td nowrap="nowrap"><code>half</code></td>
<td>See directory mode table.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x04</code></td>
<td nowrap="nowrap"><code>length</code></td>
<td nowrap="nowrap"><code>word</code></td>
<td>Length in bytes if a file, or entries if a directory.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x08</code></td>
<td nowrap="nowrap"><code>created</code></td>
<td nowrap="nowrap"><code>byte[8]</code></td>
<td>Creation time.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x10</code></td>
<td nowrap="nowrap"><code>cluster</code></td>
<td nowrap="nowrap"><code>word</code></td>
<td>First cluster of the file, or <code style="font-family: monospace">0xFFFFFFFF</code> for an empty file.
In "." entries this the first cluster of this directory's parent
directory instead.
Relative to <code style="font-family: monospace">alloc_offset</code>.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x14</code></td>
<td nowrap="nowrap"><code>dir_entry</code></td>
<td nowrap="nowrap"><code>word</code></td>
<td>Only in "." entries. Entry of this directory
in its parent's directory.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x18</code></td>
<td nowrap="nowrap"><code>modified</code></td>
<td nowrap="nowrap"><code>byte[8]</code></td>
<td>Modification time.
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x20</code></td>
<td nowrap="nowrap"><code>attr</code></td>
<td nowrap="nowrap"><code>word</code></td>
<td>User defined attribute
<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x40</code></td>
<td nowrap="nowrap"><code>name</code></td>
<td nowrap="nowrap"><code>byte[32]</code></td>
<td>Zero terminated name for this directory entry.
<br></td>
</tr>
</tbody></table>
<p>The first two directory entries in any directory are always two
dummy entries named "." and "..", in that order. In path names,
these two directory entries represent the current directory and the
parent directory, as they do in Unix, but they serve different
purposes in the file system. The first directory entry, the "."
entry, is used to store a link to the parent directory. The second
entry serves no purpose except as a place holder. The fields these
entries do not reflect state of the directories that they are
supposed to refer to. The <code style="font-family: monospace">length</code> and <code style="font-family: monospace">cluster</code> fields
are always set 0 and the <code style="font-family: monospace">modified</code> time never changes.
</p>
<p>The first directory entry in the root directory is special case.
It fills the role of the root directory's own directory entry.
Unlike the "." entry in other directories, the fields in this entry
are used and reflect the state of the root directory. In
particular, the <code style="font-family: monospace">length</code> field contains the number of
directory entries root directory. The exception is the
<code style="font-family: monospace">cluster</code> field which isn't used.
</p>
<div style="float: right; padding: 1em 0 1em 1em">
<table rules="all">
<caption>Time of Day (8 bytes)</caption>
<colgroup span="3" valign="top"></colgroup>
<colgroup span="1" valign="top"></colgroup>
<tbody><tr><th>Offset</th><th>Name</th><th>Type</th><th>Description</th></tr>
<tr>
<td nowrap="nowrap"><code>0x01</code></td>
<td nowrap="nowrap"><code>sec</code></td>
<td nowrap="nowrap"><code>byte</code></td>
<td>seconds<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x02</code></td>
<td nowrap="nowrap"><code>min</code></td>
<td nowrap="nowrap"><code>byte</code></td>
<td>minutes<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x03</code></td>
<td nowrap="nowrap"><code>hour</code></td>
<td nowrap="nowrap"><code>byte</code></td>
<td>hours<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x04</code></td>
<td nowrap="nowrap"><code>day</code></td>
<td nowrap="nowrap"><code>byte</code></td>
<td>day of the month<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x05</code></td>
<td nowrap="nowrap"><code>month</code></td>
<td nowrap="nowrap"><code>byte</code></td>
<td>month (1-12)<br></td>
</tr>
<tr>
<td nowrap="nowrap"><code>0x06</code></td>
<td nowrap="nowrap"><code>year</code></td>
<td nowrap="nowrap"><code>word</code></td>
<td>year<br></td>
</tr>
</tbody></table>
</div>
<p>The <code style="font-family: monospace">created</code> and <code style="font-family: monospace">modified</code> fields use the time format
given in the Time of Day table. All time stamps use the Japan
timezone (+9 UTC), regardless of the timezone the PS2 console was
configured to use. A four digit year used.
</p>
<p>Most of the mode flags don't serve any purpose in the structure of
the file system and only have meaning to higher level software,
like the PS2 browser. The <code style="font-family: monospace">DF_PSX</code> flag indicates that file
was copied from a PSX memory card. If the <code style="font-family: monospace">DF_POCKETSTN</code> flag
is set as well, the file is a PocketStation application file copied
from a PocketStation.
</p>
<p>Each directory entry is a massive 512 bytes long, so only two
entries fit in each 1024 cluster. The unused bytes at the end of
directory could be used for a longer name, but normally names are
truncated to only 32 bytes. File names are case sensitive, and the
characters "<code style="font-family: monospace">?</code>", "<code style="font-family: monospace">*</code>", and "<code style="font-family: monospace">/</code>" along with all
ASCII control characters are illegal in files.
</p>
</div>
</div>
<div style="clear: both">
<h2>Error Management</h2>
<p>A number of strategies are employed in the file system to handle
errors are likely to occur when using memory cards.
</p>
<div>
<h3>Error Correction Code</h3>
<p>The first line defence is the use of error correcting codes to deal
with any defects in the card's flash media. The 512 byte data area
of each page is divided into 128 byte long chunks and for each
chunk a simple 20-bit Hamming code is calculated. This code allows
a single bit error in a chunk to be both detected and corrected. A
total of three bytes are used to store this 20-bit Hamming code.
The first byte contains the column (or bit-wise) parity bits, with
the even groups in the lower nibble and the odd groups in the upper
nibble. The second and third bytes contain the even and odd groups
respectively for the line (or byte-wise) parity bits. The three
ECC bytes for each of the four 128-byte chunks of a page are stored
in order in the page's spare area.
</p>
</div>
<div>
<h3>Backup Blocks</h3>
<p>Two complete erase blocks are reserved to deal with the possibility
of the memory card being removed by the user when data is being
saved. Since writing a single cluster to card requires erasing and
reprogramming the entire erase block the cluster belongs to, a
failure during programming could destroy more then just data being
written. The two backup blocks are used to ensure the an program
operation completes atomically. Either programming completes
successfully and no data is lost, or the erase block being
programmed is left unchanged and only the new data being written is
lost.
</p>
<p>Before programming an erase block, both <code style="font-family: monospace">backup_block1</code> and
<code style="font-family: monospace">backup_block2</code> are erase. Then <code style="font-family: monospace">backup_block1</code>
programmed with a backup copy of the new data for block, and the
number of the erase block being programmed is written at the start
of the <code style="font-family: monospace">backup_block2</code>. The erase block being programmed is
then erased and programmed. Finally, <code style="font-family: monospace">backup_block2</code> is erased.
</p>
<p>Recovery from failed program operation caused by removal of the
memory card is implemented whenever a memory card is inserted into
the PS2. First <code style="font-family: monospace">backup_block2</code> is checked, if it's in a
erased state then the last programming operation completed
successfully and nothing else is done. If it's not erased, then
programming is assumed to have not been completed. The contents of
<code style="font-family: monospace">backup_block1</code> are then copied to the erase block given in
the first word of <code style="font-family: monospace">backup_block2</code>. Then <code style="font-family: monospace">backup_block2</code>
is erased.
</p>
</div>
<div>
<h3>Bad Sector List</h3>
<p>The last defence against errors is a list of bad erase blocks kept
in the superblock. If any part of an erase block is found to be
defective it can be added to <code style="font-family: monospace">bad_block_list</code>. No new
clusters in this block should be allocated, however clusters
already allocated in the block can still continue to be used.
</p>
</div>
<div>
<h3>Reserved Clusters</h3>
<p>The standard PS2 memory card drivers artificially reduce the number
allocatable clusters by rounding the number down to the nearest
1000s clusters. Since clusters in blocks in the
<code style="font-family: monospace">bad_block_list</code> don't count as against the limit, this
effectively creates a range of reserved replacement clusters. As
blocks are marked as bad, clusters in reserved range become
available and so the apparent capacity of the memory card remains
the same. <em>This was probably implemented so that memory cards
shipped with varying numbers of bad blocks would all appear to have
the same amount of free space in the PS2 browser.</em>
</p>
</div>
</div>
<div style="clear: both">
<h2>See Also</h2>
<div>
<h3>NAND Flash Memory</h3>
Micron: <a href="http://download.micron.com/pdf/technotes/nand/tn2919.pdf">NAND Flash 101: An Introduction to NAND Flash and How to Design It In
to Your Next Product</a><br>
Wikipedia: <a href="http://en.wikipedia.org/wiki/Flash_memory">Flash memory</a><br>
</div>
<div>
<h3>Error Correction Codes</h3>
STMicroelectronics: <a href="http://www.st.com/stonline/products/literature/an/10123.htm">Error Correction Code in Single Level Cell NAND Flash memories</a><br>
Micron: <a href="http://download.micron.com/pdf/technotes/nand/tn2908.pdf">Hamming Codes for NAND Flash Memories</a><br>
Hanimar: <a href="http://www.oocities.com/siliconvalley/station/8269/sma02/sma02.html#ECC">Sample code for calculating ECC values in C</a><br>
</div>
</div>
</body></html>
Reference in New Issue View Git Blame Copy Permalink