FreeRTOS+FAT cache memory
Hi All,
Any help in understanding size of cache memory which is used in below structure.
FFIOManagert *FF_CreateIOManger( FF_CreationParameters_t *pxParameters, FF_Error_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
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
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