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Directory Cache Tutorial

Describes how to configure the directory cache in a FAT file system enabled drive.

Before you start, you must:

have the knowledge of the FAT file system
have the knowledge of the directory cache
have the knowledge of the global cache manager.

The developers can configure the directory cache memory with a dynamic range. The memory allocation for directory cache on a drive depends on the available global cache memory. The global cache manager allocates memory to various cache memory on different drives. The directory cache for a drive can be configured with a dynamic range in the estart.txt file. The dynamic range configuration consists of two values :

FAT_DirCacheSizeMin specifies the minimum size of global cache to be allocated to the directory cache on a drive.
FAT_DirCacheSizeMax specifies the maximum size of the global cache to be allocated to the directory cache of a drive.

The minimum size of the directory cache is permanently reserved during the file server startup time. The maximum memory allocation depends on the available system memory and hence not guaranteed under low memory conditions.

The size of the cache memory is specified in Kilobytes. The default value for both the parameters is 128 Kilobytes.

Open the estart.txt file
to configure the directory cache.
Create a new entry for a drive, say for example drive D:
Enter the minimum size of the directory cache to be allocated to the parameter FAT_DirCacheSizeMin The value is specified in Kilobytes
Enter the maximum size of the directory cache that can be allocated when available to the parameter FAT_DirCacheSizeMax The value is specified in Kilobytes.
Repeat steps 2-4 for other drives.
Save and close the estart.txt file
Build the ROM with the modified estart.txt file

The sample entry for drive D is shown below:

[DriveD]
FAT_DirCacheSizeMin  128
FAT_DirCacheSizeMax  256

Parent topic: FAT File System