Problem mounting FAT filesystem using BOARD_SDRAM

[jon1]

I am using the RT1020 evaluation board and I am trying to get an SD Card to mount using the following example code from the sdcard_fatfs_freertos SDK demo :

if (f_mount(&g_fileSystem, driverNumberBuffer, 1U))
{
    PRINTF("Mount volume failed.\r\n");
    return kStatus_Fail;
}

If g_fileSystem resides in BOARD_SDRAM, the f_mount fails but if it is in SRAM_DTC, the function works.

Delving into the f_mount code, it calls find_volume, which calls check_fs which ends up reading sector 0 of the SD card using a call to disk_read(fs->pdrv, fs->win, sector, 1).

It would appear that reading a disc sector to a buffer (part of the g_fileSystem structure) which is in BOARD_SDRAM fails but if the buffer is in SRAM_DTC, it works. Some of the sector is read to BOARD_SDRAM but not the full 512 bytes. I don't know the technical reason for the failure but probably a timing issue due to the slower BOARD_SDRAM. 

Does anyone have any ideas for solving this problem ?

Thanks,

Jon

[Alberto_isorna]

Hello, 

Also for me disable D-cache works for me also, but I don't understand why.

Could you please explain more where the isssue comes from? 

I'm also using SDRAM and SD card together. 

[jeremyzhou]

Hi  Jon Welch

Thank you for your interest in NXP Semiconductor products and
for the opportunity to serve you.
I think I need more information about the phenomenon, whether you can introduce what modification you did about the sdcard_fatfs_freertos demo, then I can replicate this phenomenon on my site and it can help me to figure it out.
Looking forward to your reply.

Have a great day,
TIC

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[jon1]

Hi and thanks for your reply.

I can replicate the 'mount failed' error at will but the root cause is now a different failure to what I was originally seeing.

What I did was import the sdcard_fatfs_freertos demo app. On the second tab of the import option, I moved the BOARD_SDRAM option to next to top. I also added two build options to initialise the SDRAM. There were XIP_BOOT_HEADER_DCD_ENABLE=1 and SKIP_SYSCLK_INIT. Finally, I changed line 273 of sdcard_fatfs_freertos.c to read if (f_mount(&g_fileSystem, driverNumberBuffer, 1U)), ie change the option flag to 1 at the end to force the mount straight away rather than delay it.

When I built and ran the demo under the debugger, I got the mount failed error. If I moved the BOARD_SDRAM memory option back to its original place near the bottom, it ran correctly. With the SDRAM setup, the error was in the SD_SelectBusTiming routine in fsl_sd.c. However, with my original test, this function worked and I got a further error in the disc read function as per my original message. I haven't checked this out yet but will if necessary.

The original problem came to light when I added the sdcard_fatfs_freertos code to my existing app. I am using a lot of RAM for an OPC UA Server so had to use SDRAM and not SRAM_DTC. I have got around the problem temporarily by changing the declaration of g_filesystem from static FATFS g_fileSystem; to FATFS *g_fileSystem = (FATFS *) 0x20000000; to force it to use SRAM_DTC memory. This is not ideal but works until I can work out why the SDRAM option fails.

Any further advice would be appreciated, thanks.

[jeremyzhou · Accepted solution]

Hi  Jon Welch

After further testing, I find it should disable D-cache in addition above two modifications, after that the sdcard_fatfs_freertos can work now, however, its performance obvious is lower than the original version.
To disable the D-cache feature, just comment out the SCB_EnableDCache() function in the BOARD_ConfigMPU(void) function, as the below shows.
/* Enable I cache and D cache */
//SCB_EnableDCache();
SCB_EnableICache();

Have a great day,
TIC

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[jon1]

Hi,

Many thanks for your prompt reply. Your suggestion to disable the DCache has solved my problem and I can now read/write to my SDCARD using BOARD_SDRAM.

Thanks again, very much appreciated.

Jon

[jeremyzhou]

Hi  Jon Welch

Thanks for your reply.
I'd like to show the testing I did.
1) Enable DCD: adding XIP_BOOT_HEADER_DCD_ENABLE=1 and SKIP_SYSCLK_INI macros, in further, move up the BOARD_SDRAM and NCACHE_REGION, as below shows.

2) Place the g_fileSystem and g_fileSystem in the DTCM area.
__DATA(RAM3) static FATFS g_fileSystem; /* File system object */
__DATA(RAM3) static FIL g_fileObject; /* File object */

After doing the above work, I find that the demo will be stuck in the f_mkfs as below shows.

Now I'm still working on it.

Have a great day,
TIC

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[jackking]

Also, I would suspect it is because the SDRAM is cached (by default) and DTC isn't.