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uBlaze: Cannot make ram disk smaller than 3 mb

Posted by rasty1 on July 25, 2016

Hi, I'm trying to optimize a footprint and reduce size of Ram disk, but get error if I define it smaller than 3 mb. Image contains backtrace, place where it fails and some local variables. I'd appreciate any idea. https://rslutsker-gmail.tinytake.com/sf/ODUzNjA5XzM3MTEwMTE

Thanks Rasty


uBlaze: Cannot make ram disk smaller than 3 mb

Posted by rasty1 on July 25, 2016

Backtrace and variables

Attachments

ram_disk_error.png (72946 bytes)

uBlaze: Cannot make ram disk smaller than 3 mb

Posted by rtel on July 25, 2016

FAT imposes some minimum volume sizes. For example see the following thread: http://superuser.com/questions/74392/minimum-volume-size-for-fat16

The minimum size for FAT12 is smaller.


uBlaze: Cannot make ram disk smaller than 3 mb

Posted by rasty1 on July 25, 2016

How can I force it to use FAT12?


uBlaze: Cannot make ram disk smaller than 3 mb

Posted by heinbali01 on July 25, 2016

Unfortunately, the FF_Format() routine does not (yet) support FAT12, only FAT16 and FAT32.

Two parameters indicate your preference:

xPreferFAT16: try to use FAT16, if not possible, try FAT32 xSmallClusters: try small clusters first, if not possibly, try larger clusters.

Larger clusters are more efficient in terms of speed, small clusters have less waste of space.

Microsoft states that:

~~~~ if( CountofClusters < 4085 ) { /* Volume is FAT12 / } else if( CountofClusters < 65525 ) { / Volume is FAT16 / } else { / Volume is FAT32 */ } ~~~~

+FAT is following Microsoft's guidelines to get a maximum compatibility. However, you are not going to exchange your RAM disk with another system.

You could try the following in ff_format.c :

~~~~

ifdef ffconfigMINCLUSTERSFAT16
#define MIN_CLUSTERS_FAT16    ffconfigMIN_CLUSTERS_FAT16
else
#define MIN_CLUSTERS_FAT16    ( 4085 + 1 )
endif

~~~~

And define ffconfigMIN_CLUSTERS_FAT16 in your FreeRTOSFATConfig.h with a smaller value of e.g. :

~~~~ #define ffconfigMINCLUSTERSFAT16 1800 ~~~~

Regards.

Attachments

alternate (2056 bytes)

uBlaze: Cannot make ram disk smaller than 3 mb

Posted by heinbali01 on July 25, 2016

Just tested in the WIN32 demo project and it works as expected.

A 2MB RAM-disk will get 4023 clusters, a 1MB disk gets1991 clusters. In these cases, each cluster will contain a single sector of 512 bytes.


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