DMA transfer error but CFSR does not indicate bus error

[CJans.1]

I'm using a STM32H743.

I used STM32CubeMx to configure the DCMI. It uses DMA to transfer to memory.

When calling HAL_DCMI_Start_DMA(), the DCMI_DMAError() function is called.

I found out that there is a transfer error. And according the documentation a bus error is the reason.

But the CFSR register of the MCU is zero, indicating no bus error.

What could be wrong?

Things I did:

• use STM32CubeMX to set up DCMI and enable DMA
• Disabled caching
• created a buffer in SRAM1 using
  • __attribute__ ((section(".buffer"), used)) uint32_t bigbuf[30000];
  • checked that it is present in region RAM_D2
• called HAL_DCMI_Start_DMA(&hdcmi, DCMI_MODE_CONTINUOUS, (uint32_t)bigbuf, ((752*480)/4)/4);
  • HAL_OK is returned
  • sensor is 752*480, I use 8 bit DCMI (thus 4 in a word) and I use half the number of pixels and half the number of lines
• checked with oscilloscope that DCMI is working (clock, sync and data signals present)

Any idea why I can get this transfer error?

[Tesla DeLorean]

>>But the CFSR register of the MCU is zero, indicating no bus error.

The MCU doesn't do the DMA, or have visibility, as to what the DMA Controller is doing / using.

Look at the Bus Matrix, and how that relates to the DMA Unit, and the Memory you're acting on.

Some memories are not visible / usable. Be sure of where your buffer is situated.

Check alignment.

[CJans.1]

Thx Tesla DeLoran

I'm using SRAM1 which should be accesable by the DMA. It starts at 0x30000000.

You say 'Look at the Bus Matrix': Do you mean to find out what the bus error is? Or do you mean that I have to program the Bus Matrix? (I assumed STM32CubeMx does that).

[CJans.1 · Accepted solution]

I found the problem! It is a bug of STM32CubeMx.

STM32CubeMx generates this code to initalize all peripherals:

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_DCMI_Init();
  MX_I2C1_Init();
  MX_I2C2_Init();
  MX_UART5_Init();
  MX_USART1_UART_Init();
  MX_DMA_Init();
  MX_USB_DEVICE_Init();

The problem is that MX_DCMI_Init() initializes the DMA. But the DMA clock is not enabled yet! It is enabled by MX_DMA_Init().

I did not want to change the initialization order, so I enabled the DMA clock just before all the inits:

  /* USER CODE BEGIN SysInit */
 
  __HAL_RCC_DMA2_CLK_ENABLE();
 
  /* USER CODE END SysInit */
 
  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_DCMI_Init();
  MX_I2C1_Init();
  MX_I2C2_Init();
  MX_UART5_Init();
  MX_USART1_UART_Init();
  MX_DMA_Init();
  MX_USB_DEVICE_Init();

And now it works!