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PPKE ITK PhD and MPhil Thesis Classes

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1.3 CNN-UM Implementations 9<br />

the Logic Program Register (LPR) stores the LLU functions <strong>and</strong> the Switch<br />

Configuration Register (SCR) contains the setting of switches of an elementary<br />

operation of CNN cell.<br />

1.3 CNN-UM Implementations<br />

Since the introduction of the CNN Universal Machine in 1993 [22] several CNN-<br />

UM implementations have been developed. These implementations are ranged<br />

from the simple software simulators to the analog VLSI solutions.<br />

The software simulator program (for multiple layers) running on a PC calculates<br />

the CNN dynamics for a given template by using one of the numerical<br />

methods either by a gray-scale code or a black <strong>and</strong> white image <strong>and</strong> can simulate<br />

the CNN dynamics for a given sequence of templates. The software solutions are<br />

flexible, with the configuration of all the parameters (template sizes, accuracy,<br />

etc.), but they are insufficient, considering the performance of computations.<br />

The fastest CNN-UM implementations are the analog/mixed-signal VLSI (Very<br />

Large Scale Integration) CNN-UM chips [23], [20], [24]. The recent arrays contain<br />

128 × 128 <strong>and</strong> 176 × 144 processing elements [25], [24]. Speed <strong>and</strong> dissipation<br />

advantage are coming from the operation mode. The solution can be derived by<br />

running the transient. The drawback of this implementation is the limited accuracy<br />

(7-8 bit), noise sensitivity (fluctuation of the temperature <strong>and</strong> voltage), the<br />

moderate flexibility, the number of cells is limited (e.g., 128 × 128 on ACE16k, or<br />

176 × 144 on eye-RIS), their cost is high, moreover the development time is long,<br />

due to the utilization of full-custom VLSI technology.<br />

It is obvious that for those problems which can be solved by the analog (analogic)<br />

VLSI chips, the analog array dynamics of the chip outperform all the<br />

software simulators <strong>and</strong> digital hardware emulators.<br />

The continuous valued analog dynamics when discretized in time <strong>and</strong> values<br />

can be simulated by a single microprocessor, as shown in the case of software<br />

simulators. Emulating large CNN arrays needs more computing power. The<br />

performance can be improved by using emulated digital CNN-UM architectures<br />

where small specialized processor cores are implemented. A special hardware

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