Feature: Programmable logic


Accuracy and precision in on-chip synchronisation


Although many interchange the terms “accuracy” and


By Paolo Novellini, Principal Engineer, Xilinx


M


any applications would simply not exist without synchronisation, i.e., the timing coordination of events to operate systems in unison. Synchronisation is the technology that keeps local clock copies (slaves) aligned to a common reference


(master) over time – and without it, electronic systems will not operate properly. While the term “synchronisation” identifi es the general


technology, the criteria are strictly related to the applications. In Xilinx’s Versal Adaptive Compute Acceleration Platform (ACAP) there are specifi c metrics relating to synchronisation: 1. accuracy and precision, and 2. integration.


28 October 2021 www.electronicsworld.co.uk


“precision”, in measurement theory they have diff erent meanings, independent from each other. A measurement system is “precise” if repetitive measurements of the same target give results close to each other, even if not correct. Whereas it is “accurate” if repetitive measurements of the same target give results that are on average correct. Consider Figure 1, where we want to measure the position


of an object (the red dot). Two instruments (blue and green) are used for the measurement, with the cluster of blue dots representing the blue instrument’s measurements and the green dots that of the green instrument. Based on these defi nitions, the green instrument is more


accurate than the blue one, whilst the blue is more precise than the green. It also means that averaging is a good way to assess the position of an object only if the measurement system is accurate – if not, calibration is the only suitable solution.


FIFO latency T e parameters that lead the most to inaccuracies in the local clock copy come from the electronics, and specifi cally from the transceiver FIFOs. T is is because the transceiver’s FIFO has a latency that changes at each startup, and one that depends on its


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46