Every always-on system first asks one question: has anything changed? Today the answer comes from a comparator that forgets everything but the present sample, or from firmware that keeps a processor awake to run it.
The RPU answers it in hardware. It sits behind a sensor ADC, watches how fast the signal changes, adapts its threshold to the noise floor, and decides two clock cycles after each sample, with no CPU instruction in the path.
Tuned once, it keeps working as conditions change.
The RPU is a synthesizable hardware block of about 3,000 standard cells. It reads your sample stream in parallel with your existing data path. It keeps the last N samples, compares the mean of the newer half with the older half, and raises or lowers its own threshold with the noise. A constant offset cancels, slow drift stays small, an isolated spike is attenuated, and a real step or burst stands out.
When the change crosses the threshold, the decision arrives two clock cycles after the sample, every time, with zero jitter. An event shell around the core turns decisions into interrupts, caps the event rate, and reports sensor faults on a separate line, without ever touching the core.
A level comparator is memoryless. The RPU is a rate-of-change comparator with memory: a primitive that adapts to its environment and lets shells be built around it. Disconnect its wake line and your system behaves as it did before.
Its measured strength is robustness: tuned once and frozen, it keeps catching events as noise rises without flooding the CPU. It is synthesized in TSMC 65nm and SKY130 with timing met, and board-tested in a RISC-V system.
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Clone the reference RTL and run the testbench, or ask for the board kits and run our four challenge tests: blindness, tampering, silencing and determinism.
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