Hard Fault Unaligned Error on memory region from SDRAM

[Zed]

Hi everyone!

I have a working project based on STM32F746 with LCD, Ethernet and SDRAM(IS42S16160J-6TL) and now we are moving it to STM32H753II. I set up a FMC controller and tested whole SDRAM region with 8, 16, and 32 bit access. I use GCC.

During this migration I discovered a line of the code that always generate a HardFault error with UNALIGNED flag set. This is this line:

if (strncmp(data + i, boundary_str, 9) == 0)

from:

for (i = 0; i < len; i++)
{
    if (strncmp(data + i, boundary_str, 9) == 0)
    {
        boundaryOffset = i + 9;
        break;
    }
}

data is placed in SDRAM like this:

char eth_rx_buf[MAX_LENGH] __attribute__((section (".sdram_noncached")));

and boundary_str like this:

static const char boundary_str[10] = "boundary=";

HardFault happens every time when i becomes 10.

MPU settings were copied from STM32F7 project:

  /** Initializes and configures the Region and the memory to be protected
  */
  MPU_InitStruct.Enable = MPU_REGION_ENABLE;
  MPU_InitStruct.BaseAddress = 0xC0000000;
  MPU_InitStruct.Size = MPU_REGION_SIZE_16MB;
  MPU_InitStruct.AccessPermission = MPU_REGION_FULL_ACCESS;
  MPU_InitStruct.IsBufferable = MPU_ACCESS_NOT_BUFFERABLE;
  MPU_InitStruct.IsCacheable = MPU_ACCESS_NOT_CACHEABLE;
  MPU_InitStruct.IsShareable = MPU_ACCESS_NOT_SHAREABLE;
  MPU_InitStruct.Number = MPU_REGION_NUMBER3;
  MPU_InitStruct.TypeExtField = MPU_TEX_LEVEL0;
  MPU_InitStruct.SubRegionDisable = 0x00;
  MPU_InitStruct.DisableExec = MPU_INSTRUCTION_ACCESS_DISABLE;

  HAL_MPU_ConfigRegion(&MPU_InitStruct);

  /** Initializes and configures the Region and the memory to be protected
  */
  MPU_InitStruct.Enable = MPU_REGION_ENABLE;
  MPU_InitStruct.BaseAddress = 0xC1000000;
  MPU_InitStruct.Size = MPU_REGION_SIZE_16MB;
  MPU_InitStruct.AccessPermission = MPU_REGION_FULL_ACCESS;
  MPU_InitStruct.IsBufferable = MPU_ACCESS_NOT_BUFFERABLE;
  MPU_InitStruct.IsCacheable = MPU_ACCESS_CACHEABLE;
  MPU_InitStruct.IsShareable = MPU_ACCESS_NOT_SHAREABLE;
  MPU_InitStruct.Number = MPU_REGION_NUMBER4;
  MPU_InitStruct.TypeExtField = MPU_TEX_LEVEL1;
  MPU_InitStruct.SubRegionDisable = 0x00;
  MPU_InitStruct.DisableExec = MPU_INSTRUCTION_ACCESS_DISABLE;

data and boundary_str reside in 0xC0000000 part.

I have tried almost everything that I could find in Internet.

Please, give me some advice what is the cause of the HardFault. I can change this code to compare these strings one char at a time, but I want to know why it happens at all.

Thanks in advance.