Smaller embedded screens typically obtain an image source for the display from smaller embedded systems, such as Raspberry Pi or Odroid. These smaller computers are usually equipped with a single screen connector, most often an HDMI connector. Over the years, there has been a tendency to connect multiple screens to one such smaller computer, such as the new Raspberry Pi 4, which has 2 micro HDMI ports. The problem arises, however, that with such a system we switch to a multi-desktop mode, so we get two instances of the desktop. Multi-desktop mode in developing user interfaces means that we have to develop separate user interfaces (i.e. multiple programs) for each screen and then assign that user interface to each screen. However, if one of the screens in the multi-desktop mode fails, it usually transfers all the files and programs displayed on that desktop to another screen that is still running. This can cause confusion when displaying user interfaces, as the second interface may overlap the first.
In this paper, we present the well-known concept of displaying a larger image where individual screens show only a part of that image. Many examples like this can be seen in New York's Times Square, where they display various content (usually ads) on such systems. Such a system is also in the lobby of the Faculty of Electrical Engineering where 9 screens display one larger image. Smaller embedded screens come in a wide variety of resolutions which is why we can't use commercial products as these are usually made to display standard resolutions.
To realize the concept we used Digilent's development board which is based on Xilinx's FPGA chip of the Artix family. The necessary printed circuit boards were made to connect Densitron's Aurora embedded computer, and printed circuit boards were connected to connect the embedded screens to the development board. The system is based on VDMAs (Video Direct Access Memory) which are components that read and write blocks of information (images) in and out of external memory without the intervention of a microcontroller. So the embedded computer sees the system as a larger screen, so it sends a higher-resolution image to the FPGA, and the VDMAs then divide the individual parts into specific screens. This way we get rid of multiple desktop mode and the user interface developer can develop only one program and then cut the user interface according to the layout of the screens.
In our assignment, we took two built-in screens with a resolution of 1440x240 with the ability to transmit touch information. In addition to the image transfer itself, we also had to manipulate the touch information.
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