Embedded Systems

Giving eyes to a micro controller: DCMI interface on an STM32F4

It has been another long hiatus between posts. But, I have managed to learn and do quite a bit of stuff in these last few months and it has been rewarding to say the least.

Recently, I have had to work on an embedded platform for image processing. It was quite a big deal as I had never worked with any sort of embedded platform before and the kind of work is quite different from what I have done before. So, my first task was to interface a camera with a microcontroller. After consulting with my friends, Shrenik and Vinod, I decided to use a microcontroller which provides a hardware camera interface instead of writing the complete firmware from scratch for an ATMEGA as I had planned on doing earlier.

After some research, I ended up selecting the well known STM32F4 series of microcontrollers. The STM32F407 is a high powered μC with an ARM Cortex M4 processor running at 168 MHz. The development board available has 1 Mb of onchip flash and 192 kB of SRAM. After playing with GBs of RAM, it sure was tough to be excited about a few kB of SRAM, but it was a different challenge to solve the problem using as few resources as possible. The STM32F407 features a a hardware camera interface known as DCMI ( Digital Camera Interface). It is compatible with a huge range of camera modules on the market.

I had also decided to use the OV2640 camera module as it features an on-board JPEG encoder and is quite well documented. After a few days of familiarizing with the basic concepts and fiddling around with the standard peripherals library from  STM, I came across this amazing implementation, OpenMV. I found it extremely helpful to understand the intricacies of image processing on embedded systems.

The primary issues that I faced while working on this project were:

  • Understanding DCMI and DMA interfaces of the STM32 controller.
  • Understanding the communication and synchronization between the camera and the controller.
  • Clocks and STM’s unique proposition of allowing us to turn off peripheral clocks when required for low power usage.

I am going to be blogging about my experiences regarding my foray into the world of micro-controllers and camera control soon. Until then, here are a few images that I captured with my setup.