FATFS on SD card have some error when D-cache is enabled

[ClockZLZ]

All my code works on RTOS.

When I enable D-Cache，fs_mount() from FATFS on SD card returns FR_NO_FILESYSTEM，SD card can not work.

When I disable D-Cache, fs_mount() returns FR_OK, SD card can write and read.

But at the same time , i need to use Ethernet on my device . When I close D-Cache, my Ethernet can not work.

How can I resolve these two conflicting issues？

[Andrew Neil]

FatFS is open-source.

So step into fs_mount()  and see exactly where it is failing, and what causes that failure.

Similarly, step the code in the working case and see where it differs.

PS:

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@ClockZLZ wrote:

at the same time , i need to use Ethernet on my device . When I close D-Cache, my Ethernet can not work.

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Are you sure that the issue is actually to do with D-Cache, or is it some other conflict between your Ethernet & SD-Card stuff ...?

[SofLit · Accepted solution]

Hello @ClockZLZ and welcome to the community.

Most probably it's something related to cache coherency/maintenance.

See this thread:

https://community.st.com/t5/stm32-mcus-embedded-software/fatfs-f-open-fails-when-data-cache-is-enabled/td-p/110777

[Pavel A.]

> When I close D-Cache, my Ethernet can not work.

Does it crash / catch exception or fault when you disable D-cache? Ethernet should work even without D-cache, at least on older 'H7 such as H743.

Using the Cortex-M7 D-cache correctly is not trivial, this is why it is not enabled by default. When the cache is disabled, most libraries made for Cortex-M4 can be reused as is.

[ClockZLZ]

My SD card problem is the same as：

Solved: Re: fs_mount() from FATFS on SD card returns FR_NO... - STMicroelectronics Community

The Ethernet part is maintained by my colleague，i will make sure if there is any other conflict between your Ethernet & SD-Card.

thank you for your opinion！

[ClockZLZ]

Thank you very much for your opinion !

No crash or fault occure when I disable D-cache. In fact , in order to make Ethernet work will , I enable D-cache and MPU for it. 

If you are sure Ethernet can work without D-cache.  I will have a try.

[ClockZLZ]

it's usef to uncomment L63 in sd_diskio.c to activate Cache maintenance:

/* USER CODE BEGIN enableSDDmaCacheMaintenance */
#define ENABLE_SD_DMA_CACHE_MAINTENANCE  1 
/* USER CODE END enableSDDmaCacheMaintenance */

After doing this my SD Card can mount successfully when D-cache is enabled.

[Pavel A.]

> If you are sure Ethernet can work without D-cache.  I will have a try.

I got it working on STM32H743/53 with some previous version of ST libraries and ETH driver, not sure that the current will work as is. Hardware itself does work with properly assigned memories and no D-cache.