Configuring DCMI / DMA to truncate 2 least significant bits of 10-bit pixel stream

[vrbadev]

I currently use the STM32H7 MCU with CMOS monochrome imaging sensor connected via 10-bit parallel DCMI interface. However, when wired this way to the MCU the grayscale pixels are stored as 16-bit unsigned integers in the memory.

Is there any way to configure the DCMI peripheral (or the DMA transferring the pixel values to the SRAM memory) to truncate the 2 least significant bits of the values (so they can be stored as 8-bit unsigned integers)? I didn't find any solution or suggestions in the documentation of the peripherals.

Thanks for any help.

EDIT: The question is about the 2 least significant bits. The DCMI_D[1:0] are the least significant bits I need to remove and keep only DCMI_D[9:2]. The DMA/DCMI would have to be able to perform logical shift right by 2 bits to remove them and to get the desired 8-bit result, which is the point of this question.

[waclawek.jan]

Couldn't you just simply set DCMI to 8-bit data?

 

JW

[vrbadev]

No, because the pins DCMI_D[0] and DCMI_D[1] are the least significant bits. So I need to keep DCMI_D[9:2] when using 10-bit interface, not DCMI_D[7:0] as presented in the docs. I corrected the question to two least significant bits.

[FBL]

Hello @Vojtěch Vrba​ 

I am not sure if this helps but you may need to check AN5020. Hope this helps!

[vrbadev]

Thanks, but no, this does not explain how to store D[9:2] to form 8-bit image in memory.

[waclawek.jan]

> No, because the pins DCMI_D[0] and DCMI_D[1] are the least significant bits. So I need to keep DCMI_D[9:2] when using 10-bit interface, not DCMI_D[7:0] as presented in the docs.

> The DMA/DCMI would have to be able to perform logical shift right by 2 bits to remove them

If you can't find it in RM, it's not there.

Meantime, couldn't you simply connect camera's data pins 2..9 to mcu's data pins 0..7?

JW

[vrbadev]

Well if the peripherals don't support it, I cannot do anything about it. I would have to desing a new PCB for the CMOS sensor to solve it by wiring the interface as you suggest.