Raspberry Pi as a measurement system control unit

In this paper a system for measuring temperature in an FPGA structure is proposed. In this arrangement the Spartan-3 XC3S200 programmable FPGA device was tested and the popular small educational microcomputer Raspberry Pi, was employed as a control unit for the whole system. Part of the system was implemented inside the tested structure. There was an array of ring oscillators as temperature sensors and a structure for controlling the array. Ring oscillators are often implemented in FPGA devices. They are used both as single elements or an array of sensors for measuring the chip´s temperature or path delay of SUT. The sensors can be located in different areas of the chip. In the case of this tested device 36 sensors were used, but generally, their number depends on the designer. The ring oscillator´s frequency depend on the temperature, and the frequency of the activated sensor was measured outside with an oscilloscope. The Raspberry Pi controlled the measurement process via an SPI and the results were collected from the oscilloscope via a UART/RS232 interface. 2D and 3D visualizations of the frequency to temperature relationship were made using Gnuplot and Scilab. The results should visualize the temperature distribution inside the device, but first, the right calibration of sensors should be performed.