Occur RuntimeError when using set_windowing

RAYMOND · August 9, 2023, 11:22am

Hi,

I’m using set_windowing() in openmvH7 and RuntimeError happened.

Here is the code:

import sensor, image, time
sensor.reset()
sensor.set_pixformat(sensor.RGB565)
sensor.set_framesize(sensor.VGA)
sensor.skip_frames(time = 2000)
sensor.set_windowing((134,243,113,110))
clock = time.clock()
img = sensor.snapshot()
while(True):
	clock.tick()
	img = sensor.snapshot()

But the code work well in openmv4 plus,I am quite confused.

Thanks for any help.
Raymond

kwagyeman · August 9, 2023, 5:16pm

Hi, which line of code is throwing the error?

If it’s snapshot then the issue is related to you asking for a buffer size that’s not aligned per all the DMA rules. To fix that just add a pixel to the window to have even boundaries.

Our code is pretty mature at this point on handling all types of crops and resolutions. If it can’t handle something it reliably catches the error instead of breaking.

RAYMOND · August 10, 2023, 5:44am

yes,it’s the snapshot throwing the error.So if I change

sensor.set_windowing((134,243,113,110))

into

sensor.set_windowing((134,243,110,110))

the code would just work well?

kwagyeman · August 10, 2023, 5:36pm

It’s probably the odd numbers you are using:

github.com

openmv/openmv/blob/master/src/omv/ports/stm32/sensor.c#L779


      
          uint32_t dma_line_width_bytes = resolution[sensor->framesize][0] * bytes_per_pixel;
          
          // Shrink the captured pixel count by one word to allow cropping to fix alignment.
          if (x_crop) {
              dma_line_width_bytes -= sizeof(uint32_t);
          }
          
          length = dma_line_width_bytes * h;
          
          // Error out if the transfer size is not compatible with DMA transfer restrictions.
          if ((!dma_line_width_bytes)
              || (dma_line_width_bytes % sizeof(uint32_t))
              || (dma_line_width_bytes > (OMV_LINE_BUF_SIZE / 2))
              || (!length)
              || (length % DMA_LENGTH_ALIGNMENT)) {
              return SENSOR_ERROR_INVALID_FRAMESIZE;
          }
          
          // Get the destination buffer address.
          vbuffer_t *buffer = framebuffer_get_tail(FB_PEEK);

So, Chang the 243 to 244 and 113 to 114 or etc.

But, what’s happening is that the system computed all the DMA line widths and did all the pixel calcs and it found the solution doesn’t work. So, just adjust the window until it stops complaining.

Once you have a valid solution here it’s 0 CPU load to capture an image. The whole process is DMA accelerated with just 1 interrupt to the CPU per frame.