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FreeRTOS+FAT cache memory

Posted by sachingole on June 7, 2017

Hi All,

Any help in understanding size of cache memory which is used in below structure.

FFIOManagert *FFCreateIOManger( FFCreationParameterst *pxParameters, FFError_t *pxError );

This FFIOManagert object has variable ulMemorySize, whose description says that it shoud in mutiple of sector size.

/* The size of the cache memory. ulMemorySize is specified in bytes and must be a multiple of ulSectorSize. */ uint32_t ulMemorySize;

I have STM32476-RG Nucleo board with 128 KB RAM, In which I have created 25KB ramdisk so I would to cache memory size as minimum as possible.

What is recommended size for cache memory size ? What shoud be criteria to decide apropriate size ?

Best regards, Sachin


FreeRTOS+FAT cache memory

Posted by heinbali01 on June 8, 2017

HI Sachin, I just measured the actual use of the +FAT internal cache buffers.

In a test I sent and received 25 files using 3 FTP threads.

When copying to and from an SD-card, I used large (5MB) files, so 3 files were written and read simultaneously.

The result is surprising: in all cases, at most 9 buffers were used:

~~~ RAM-disk: Buffers 9 / 15 SD-Card : Buffers 9 / 128 ~~~

So I would provide at least 9 x 512 ( =4608 ) bytes as caching memory. Later on, have a try with less if you like.

Note that in most cases, the internal caches are by-passed: FF_Write() and FF_Read() are optimised so that user-buffers are passed directly to the drivers.

What is recommended size for cache memory size ?

9 x 512 bytes

What should be criteria to decide appropriate size ?

Look at how many files are open at the same time and how many tasks are accessing the same volumes (RAM-disk, SD-card). It should not get locked-up; task waiting for ither tasks.

There is a time-out when waiting for a free cache buffer: grep for FF_GETBUFFER_WAIT_TIME_MS, by default 20 seconds.

Regards.


FreeRTOS+FAT cache memory

Posted by sachingole on June 8, 2017

Thank you for deterministic reply.

In my case I will be using 1 file at a time, at most I will be working on 2 files only. So I am setting

define mainIO_MANAGER_CACHE_SIZE ( 5UL * mainRAM_DISK_SECTOR_SIZE )

Best regards, Sachin


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