Abstract :
Throughout its twenty-five year history, logic emulation architectures have been governed by Rent´s Rule. This empirical observation, first used to build 1960s mainframes, predicts the average number of cut nets that result when a digital module is arbitrarily partitioned into multiple parts, such as the FPGAs of a logic emulator. A fundamental advantage of emulation is that, unlike most devices, FPGAs always grow in capacity according to Moore´s Law, just as the designs to be emulated have grown. Unfortunately packaging technology advances at a far slower pace, leaving emulators short on the pins demanded by Rent´s Rule. Many cut nets are now sent through each package pin, which costs speed, power and area. At today´s system-on-chip level of design, the number of system-level modules is growing, while their sizes are remaining constant. In the meantime, FPGAs have grown from a handful of logic lookup tables (LUTs) at the beginning to over a million LUTs today. At this scale, an entire system-level module such as an advanced 64-bit CPU can fit inside a single FPGA. Fewer module-internal nets need be cut, so Rent´s Rule constraints are relaxing. Fewer and higher-level cut nets means logic emulation with megaLUT FPGAs is becoming faster, cooler, smaller, cheaper, and more reliable. FPGA´s Moore´s Law scaling is escaping from Rent´s Rule.
