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Need help to understand Firmware UART_TwoBoards_ComDMA

Question asked by julien.terrier on Aug 7, 2015
Latest reply on Sep 5, 2015 by julien.terrier
Hello everybody,
I want create a project wich work with USART, I use as IDE Keil µvision5 (light version) then I bought a STM32F429ZI-DISCOVERY board to train with it. 
Currently I trying to understand how does it work, indeed I saw that I need two boards for the program to work.
Actually I trying to understand "UART_TwoBoards_ComDMA" project.
 In the packages, I have three example wich use the USART protocol:
To lead my project with success I need  someone who has a knowledge on the µcontroller such as STM32F4 and who can help me througout this forum.
Of course I have started to read the relevant datasheet such as STM32F4 ref manual and STM32F429ZIT to learn the register and how does it work.
But as I am beginner in embedded firmware its very hard to undestand everything.
My first question will be:
What is the significant difference between this 3 examples (DMA, INTERRUPT and POLLING) ?
I saw that the DMA is used as internal data bus ? and I know that the interrupt  for example it make with a timer.
I hope that my post is clear but I am french and beginner.
Thank you so much.