Hierarchical Event Readout with Asynchronous Pipelined Opportunistic Merges
Leo Liu, Kwabena A. Boahen · 2025
Event cameras asynchronously output a stream of words that encode the location, time, and sign of a luminance change that a pixel detects. When these events are sparse, one is read out of a 1024-by-1024-pixel with a 352ns latency, the time it takes to cycle from one row to another. But when more than one event occurs per cycle, this readout latency balloons to 180μs, the time it takes to cycle through half of the rows. Here we shorten this queue by reading out single events faster. Instead of selecting and addressing rows and columns, we select and address squares of exponentially increasing size. A 5-level–16-ary tree merges these squares’ events hierarchically in a predetermined order. Asynchronous pipeline stages break up long datapaths to output a 16-bit word every 5ns, read an event out with a 51ns latency, and stream out events from all 1M pixels in 350μs (3.0Geps). By reading a single event out 7 times faster than row–column, hierarchical shortens the queue 500-fold and cuts latency 3,500-fold.