Hi ST Community,
I'm working on an STM32H755ZIT6 project where I'm interfacing an SD card using SDMMC1 + DMA and FATFS (with exFAT) from the Cortex-M7 core. However, I'm facing a strange issue: the first time the board runs after programming, it writes and reads English text correctly to/from the SD card, but after one or two resets, the file content becomes garbled or shows Chinese-like characters instead of English. I suspect this may be cache, MPU, or alignment-related, but I'm not sure what I’m missing.
Here is a detailed overview of my configuration and setup:
1. MCU and Core Context
MCU: STM32H755ZIT6
- Core used for SD card operations: Cortex-M7
2. SDMMC1 Peripheral Configuration
SDMMC Mode: SD 4-bit Wide Bus
SDMMC1 Clock Divide Factor: 0x04 (Targeting 50 MHz actual clock)
SDMMC1 Interrupt: Enabled, priority set in NVIC to 14
3. Clock Configuration
SYSCLK = 400 MHz
CPU1_CLK (M7) = 400 MHz
CPU2_CLK (M4) = 200 MHz
PCLK = 200 MHz
SDMMC1_CLK = 200 MHz
Actual SDMMC1 Clock = 200 MHz / 4 = 50 MHz
4. FATFS Middleware Settings (For Cortex-M7)
FATFS enabled under FATFS_M7
Filesystem: exFAT
LFN Mode: Static allocation, work buffer in .bss
Enabled DMA Template
Platform setting:
Card Detect Pin: PA0 (SDMMC1_uSD_DETECT)
5. MPU and Cache Configuration
CPU I-Cache: Enabled
CPU D-Cache: Enabled
MPU Region 1 (AXI SRAM Region):
Base Address: 0x24000000
Size: 512KB
Access: Full access
TEX: Level 1
Shareable: Disabled
Cacheable: Disabled
Bufferable: Disabled
(MPU Region 0 is default)
6. NVIC Settings
SysTick Timer Priority: 14
SDMMC1 IRQ Priority: 14
7. Linker Settings
Minimum Heap: 0x400
Minimum Stack: 0x800
(for both M7 and M4)
8. Code Behavior
Location: CM7/Core/main.c
9. Key Operations:
Mount filesystem
Format (optional)
Write simple text: "[CORE_CM7]: Hello FATFS"
Read back to an aligned 32-byte buffer rtext[64]
Compare with original
All file I/O is wrapped with error checks and logs printed over UART using printf().
SD Card Info
Capacity: 128GB
Format: exFAT with 32KB cluster size
CODE:
ALIGN_32BYTES(uint8_t rtext[64]); // Read buffer, 32-byte aligned
uint8_t workBuffer[_MAX_SS]; // Work buffer for exFAT formatting
int main(void)
{
printf("[CORE_CM7]: Program Starting... \r\n");
// Perform file operations
FS_FileOperations();
}
static void FS_FileOperations(void)
{
FRESULT res;
uint32_t bytesWritten, bytesRead;
uint8_t wtext[] = "[CORE_CM7]: Hello FATFS";
// Mount the SD card
res = f_mount(&SDFatFS, (TCHAR const*)SDPath, 0);
if (res != FR_OK)
{
printf("[CORE_CM7/FatFs]: Failed to mount SD card (error: %d)\n", res);
Error_Handler();
}
// Open file for writing
res = f_open(&SDFile, "TEST.TXT", FA_CREATE_ALWAYS | FA_WRITE);
if (res != FR_OK)
{
printf("[CORE_CM7/FatFs]: Failed to open file for writing (error: %d)\n", res);
Error_Handler();
}
// Write to file
res = f_write(&SDFile, wtext, sizeof(wtext), (void*)&bytesWritten);
if (res != FR_OK || bytesWritten != sizeof(wtext))
{
printf("[CORE_CM7/FatFs]: Write failed (error: %d, bytes written: %lu)\n", res, bytesWritten);
Error_Handler();
}
f_close(&SDFile);
// Open file for reading
res = f_open(&SDFile, "STM32.TXT", FA_READ);
if (res != FR_OK)
{
printf("[CORE_CM7/FatFs]: Failed to open file for reading (error: %d)\n", res);
Error_Handler();
}
// Read from file
res = f_read(&SDFile, rtext, sizeof(wtext), (void*)&bytesRead);
if (res != FR_OK || bytesRead != bytesWritten)
{
printf("[CORE_CM7/FatFs]: Read mismatch (error: %d, read: %lu, expected: %lu)\n", res, bytesRead, bytesWritten);
Error_Handler();
}
f_close(&SDFile);
// Compare buffers
if (Buffercmp(rtext, wtext, bytesWritten) == 0)
{
printf("[CORE_CM7/FatFs]: Data written and read are identical\n");
}
else
{
printf("[CORE_CM7/FatFs]: Data mismatch – printed text appears garbled\n");
Error_Handler();
}
}
static uint8_t Buffercmp(uint8_t* pBuffer1, uint8_t* pBuffer2, uint32_t BufferLength)
{
while (BufferLength--)
{
if (*pBuffer1 != *pBuffer2)
return 1;
pBuffer1++;
pBuffer2++;
}
return 0;
}--------------------------------------------------
NVIC
FTFS
Cortex M7
Request for Help
Could someone from ST or the community please:
Review my configuration and highlight any potential issues?
Suggest any MPU/cache settings or APIs I might be missing (e.g., cache invalidation)?
Advise whether switching from DMA to MDMA would improve performance or stability in this context, and if so, how should I configure MDMA for SDMMC1 (step-by-step or with CubeMX guidance)?
If possible, share a working example or reference for STM32H7 + SDMMC + FATFS + DMA or MDMA, including MPU/cache setup and buffer alignment practices?
Any help would be greatly appreciated!
