Why do I get overrun error when using DCMI?

[YL.11]

BACKGROUND

project purpose: capture a picture every 2 seconds

board: nucleo stm32h743zi2 at 480MHz

ide: stm32cubeide

camera module: ov7670 at 24MHz

CONFIGURATION

The project was initialized using stm32cubeMX with I2C and DCMI initialized. The ov7670 is configured with QVGA resolutions and RGB565. I can confirm the ov7670 is properly configured because the debugger shows that each it_vsync contains 240 it_hsync (can be count using the interruption).

I have tried configuring the DMA with the following configurations:

• DMA0/DMA1 Stream0-5
• With and without FIFO
• Normal Model and Circular model

Here is the main.c (only the part I added):

uint8_t framebuf[320 * 240 / 2];
void ov7670_Init() {
	ov7670_Stop();
	ov7670_Write_Reg(0x12, 0x80);  // RESET
    HAL_Delay(30);
    for(int i = 0; ov7670_reg[i][0] != REG_BATT; i++) {
    	ov7670_Write_Reg(ov7670_reg[i][0], ov7670_reg[i][1]);
    	HAL_Delay(1);
    }
}
 
...
 
int main(void)
{
  ...
  ov7670_Init();
  while (1)
  {
	  HAL_Delay(2000);
	  HAL_DCMI_Start_DMA(&hdcmi, DCMI_MODE_SNAPSHOT, framebuf, 320*240/2);
  }
}

PROBLEM

Well, I can get the image bytes in the DR register of DCMI instance but the hdcmi->ErrorCode is 0 in the first 2 seconds and then becomes 65 (0x41), which I think means overrun error. The DMA2_Stream1_IRQHandler can trigger. The elements of framebuf are always random numbers. I did not do anything with the framebuf yet after capturing it.

So all together, I can the problem is related to the DMA settings.

Any idea how to solve the problem?

[YL.11]

anybody can help?

[YL.11 · Accepted solution]

Weeks have been spent before finally get things to work. I have to complian the code quality generated by cubeMX. After switching MX_DMA_Init() and MX_DCMI_Init() in the main.c file which is automatically generated, everything works fine.:dizzy_face:

[Florian Moser]

Thanks for sharing your solution!

Had the exact same problem with my STM32H7A3IITxQ. Switching these functions also worked for me.

Seems like it hasn't been fixed in the last 2 years.

[Microman]

Another hint for DCMI and DMA overrun issues

Just to mention and help avoiding others to fall into the same overrun trap like me:

Check to which power domain the DCMI and DMA is connected to and which memories are usable for a DMA transfer!

I set up a demo code using Cume MX and it was placing everything in DTCM (from 0x2000'0000).

This code caused permanent overuns because DMA1 can not transfer data to the DTCM.

Always check that your frame buffer is in SRAM1 or somethin else that supprots the reception of data from DMA.
For example define your framebuffer variabl with a placement precompiler directive. (SRAM1 area needs to be defined in the linker file as well)

u8 frameBuffer[DCMI_FRAMESIZE] @ "SRAM1";