Bottom-up and top-down neuromorphic processor design : Unveiling roads to embedded cognition

While Moore's law has driven exponential computing power expectations, its nearing end calls for new roads to embedded cognition. The field of neuromorphic computing aims at a two-fold paradigm shift compared to conventional computing. First, it investigates the co-location of processing and memory in neurons and synapses. Second, it aims at encoding data both in space and time with all-or-none spike events. However, it is unclear which of the bottom-up (neuroscience-driven) or top-down (application-driven) design approaches could unveil the most promising roads to embedded cognition. In order to clarify this question, this thesis is divided into two parts. The first part focuses on the bottom-up approach. From the building-block level to the silicon integration, we design two bottom-up neuromorphic processors: ODIN and MorphIC. We demonstrate with measurement results that hardware-aware neuroscience model design and selection allows reaching record neuron and synapse densities with low-power operation. However, the inherent difficulty for bottom-up designs lies in applying them to real-world problems beyond the scope of neuroscience applications. The second part investigates the top-down approach. By starting from the applicative problem of adaptive edge computing, we derive the direct random target projection (DRTP) algorithm for low-cost neural network training and design a top-down DRTP-enabled neuromorphic processor: SPOON. We demonstrate with pre-silicon implementation results that combining event-driven and frame-based processing with weight-transport-free update-unlocked training supports low-cost adaptive edge computing with spike-based sensors. However, defining a suitable target for bio-inspiration in top-down designs is difficult, as it should ensure both the efficiency and the relevance of the resulting neuromorphic devices. Therefore, we claim that each of these two design approaches can act as a guide to address the shortcomings of the other.