作者：Apollo5520

轉自：http://blog.chinaunix.net/uid-8087110-id-1989039.html

1、起初我的wince bsp 在插入8G u盤時需要等待大概40秒左右才出現盤符，這個速度簡直無法忍受。 2、經過分析，發現比較耗時的是位于文件 C:\WINCE500\PUBLIC\COMMON\OAK\DRIVERS\FSD\FATUTIL\MAIN\scandisk.cpp內的 ScanVolumeInternal 函數 ，這個函數是用來掃描文件系統的，如果能夠去掉插入sd卡或U盤時不自動掃描則可以大大縮短出現盤符的時間。 3、經過分析發現這個是有FATFS相關注冊表進行控制的

[HKEY_LOCAL_MACHINE\System\StorageManager\FATFS] "MountFlags"=dword:0 ; "Flags"=dword:14 ;

具體的控制是Flags項，這個分支定義的是整個FATFS的參數，如果想進行分類進行不同的定義，則需要修改相關注冊表分支，例如，想定義flash自動掃描則添加定義如下

[HKEY_LOCAL_MACHINE\System\StorageManager\Profiles\FlashDrv\FATFS] "MountFlags"=dword:2 "Flags"=dword:10 ;在Profiles\FlashDrv添加FATFS分支定義falsh上FATFS文件系統的相關參數，其他的sd卡，U盤等也可分別進行定義

以上兩個分支可同時存在，進行詳細的的定義。

關于FATFS相關參賽的定義如下：（http://msdn.microsoft.com/en-us/library/ms885403.aspx）

Platform Builder for Microsoft Windows CE 5.0 FAT File System Registry Settings

The file allocation table (FAT) file system retrieves driver specific settings from the registry.

The following table shows the registry settings for the FAT file system stored inHKEY_LOCAL_MACHINE\System\StorageManager\FATFS.

Registry value: TypeDescription

BufferSize: REG_DWORD	Specifies the number of sector-sized buffers to use for streams. The default value is 64 for TFAT and 32 for FAT.
CacheSize: REG_DWORD	Indicates the size of the disk cache, in number of sectors. This value must be a power of 2 and at least 16 sectors. If set to zero, FATFS will determine the best cache size to use. For more information, see CacheSize registry subkey.
CodePage: REG_DWORD	Overrides CP_OEMCP in all character conversions.
Dll: REG_SZ	Specifies the name of the file system DLL.
EnableCache: REG_DWORD	Controls caching. 0 - Disables caching 1 - Enables caching
EnableCacheWarm: REG_DWORD	Enables pre-warming of the cache.
Flags: REG_DWORD	Indicates FAT file system registry flags. For more information, see Flags registry subkey.
FormatTfat: REG_DWORD	Formats the volume as TFAT on auto-format or through IOCTL_DISK_FORMAT_VOLUME.
FriendlyName: REG_SZ	Specifies a friendly name for the file system.
MountLabel: REG_DWORD	Pulls the volume label and uses it as a mount point.
Paging: REG_DWORD	Controls paging. 0 - Disables paging 1 - Enables paging
Util: REG_SZ	Specifies the DLL name of utility to do format and scan.

Flags registry subkey

The following table shows the available values you can set for the Flags registry subkey; set Flags to a combination of these values.

FlagValueDescription

FATFS_UPDATE_ACCESS	0x00000001	Updates access times.
FATFS_DISABLE_LOG	0x00000002	Disables event logging.
FATFS_DISABLE_AUTOSCAN	0x00000004	Disables automatic calls to ScanVolume.
FATFS_VERIFY_WRITES	0x00000008	Verifies all writes.
FATFS_ENABLE_BACKUP_FAT	0x00000010	Adds a backup FAT to all formats.
FATFS_FORCE_WRITETHROUGH	0x00000020	Sets all files to WRITE_THROUGH, regardless of the parameters to CreateFile.
FATFS_DISABLE_AUTOFORMAT	0x00000040	Disables automatic formatting of unformatted volumes.
FATFS_WFWS_NOWRITETHRU	0x00010000	Disables write through on the WriteFileWithSeek function. Improves memory-mapped file performance.
FATFS_DISABLE_FORMAT	0x00020000	Disables format.
FATFS_TRANS_DATA	0x00040000	Transacts data on a write operation.
FATFS_TFAT_USECLUS1	0x00080000	Uses the cluster 1 entry in the FAT table for a TFAT transaction. TFAT uses the NOF field of the boot sector by default.
FATFS_DISABLE_TFAT_REDIR	0x00100000	Disables the redirect of the root directory to another hidden directory for FAT12 or 16.
FATFS_TFAT_ALWAYS	0x00200000	Marks transaction status, even if only one sector in FAT is changed.
FATFS_FORCE_TFAT	0x00400000	Forces TFAT transactions even if the volume is not formatted as TFAT.

CacheSize registry subkey

The CacheSize registry subkey is a hexadecimal number of sectors to cache. This has to be a power of two. The following table shows valid numbers for theCacheSize registry subkey.

Registry entryNumber of sectorsCache in kilobytes (KB)

2	2	1
4	4	2
8	8	4
10	16	8
20	16	32
40	64	32
80	128	64
100	256	128
200	512	256
400	1024	512
800	2048	1024
1000	4096	2048

Example

The following registry key example shows the location of the Flags andCacheSize registry subkey values.

Copy Code [HKEY_LOCAL_MACHINE\System\StorageManager\FATFS]"Flags": dword:00000024"CacheSize" = dword:400

If CacheSize is set to zero, the cache size will be set automatically.

?

http://www.vckbase.com/document/viewdoc/?id=1267

對”Flags”值的描述如下（C:\WINCE500\PRIVATE\WINCEOS\COREOS\FSD\FATFS\fatfs.h）：
　

標志	值	描述
FATFS_UPDATE_ACCESS	0x00000001	更新訪問時間
FATFS_DISABLE_AUTOSCAN	0x00000004	不能自動調用ScanVolume
FATFS_VERIFY_WRITES	0x00000008	檢驗所有寫操作
FATFS_ENABLE_BACKUP_FAT	0x00000010	備份FAT表
FATFS_FORCE_WRITETHROUGH	0x00000020	讓系統可以直接將任何緩沖區中的數據寫到磁盤上，這樣系統將加快寫數據到磁盤的速度
FATFS_DISABLE_AUTOFORMAT	0x00000040	禁止自動格式化未格式化的分區
FATFS_DISABLE_COMPCHECK	0x00000080	禁止自動檢測壓縮分區

上面把FLAGS定義為 14，也就是備份FAT表、不自動掃描卷標。這樣8G的SD卡，3秒就可以出現盤符了。

? 原創文章，轉載請注明：轉載自 風雨無阻博客（http://Apollo5520.cublog.cn） 本文鏈接地址：http://blog.chinaunix.net/u3/105764/showart_2114352.html ?

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