Design of an embedded system for video performance measurements
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This master's thesis describes the design process of a measurement instrument for measuring the video playback performance. The purpose of the instrument is to aid in optimizing the video playback quality of devices such as tablets, smartphones and televisions. In particular, the instrument measures the frame rate and number of missing frames using a sensor attached to the display. The aspect that sets this instrument apart from common ways of measuring display frame rates is that it operates outside the video playback device. This means that no modifications are required to the device being tested, and all effects that may occur in e.g. display hardware are accurately measured. In this way it allows more complete analysis of the device behaviour, and is also suitable for testing competitor's devices. To implement the measurement instrument, a custom hardware platform based around the STM32F407 microcontroller is designed. In order to adapt to the rapidly changing needs and focuses of the market sector, the hardware is designed with maximal extensibility to allow easy attachment of new kinds of sensors. The signal processing required for the sensor signals is implemented entirely in software, in order to allow future measurement tasks to use different algorithms. This places requirements on real-time performance on the hardware and software, and the NuttX real-time operating system is chosen as a basis for the firmware development. A software architecture composed of signal processing libraries, low-level device drivers and GUI user interface is described. The architecture is designed to allow easy reuse of components to implement several measurement tasks. Finally, the success of the project is evaluated both on basis of meeting the set goals and based on feedback received from the pilot customers and sales team. The development of the instrument took 9 months from the initial planning meetings to the first official software version. Characterization measurements have shown the instrument to measure up to 150 FPS frame rates at 1 ms resolution.