Why did the gated weight-stationary engine need so much synthesis memory, and does fixing it change its area verdict?

What it found

The accumulator read in the engine of accel-gatedrtl indexed the whole accumulator bus with a variable, which Yosys builds as one wide shifter per lane and which stopped accel-gatedlanes at 16 lanes. An AND-OR read mux over the batch sets gives the same cycles, fetches, accumulator writes and flop count, bit-exact against NumPy at all 48 points (P = 2–64, B = 4 and 8), but weight-stationary engines come out 17–28% smaller in SKY130 HD synthesis (output-stationary unchanged). Gated weight-stationary is 1.45–1.50× the output-stationary area at B = 4 and 2.1–2.2× at B = 8, flat in P, against 1.6–1.9× and 2.9–3.0× before; every point now synthesises under the old 7 GB cap. Stylised: synthesis only, one layer shape, random data, clock-pin-only energy; the cause is inferred from the before-and-after effect.

A figure from its own output

Paper, code and results

• README and method
• Experiments and results
• Code
• Tests

More in Task-specific AI accelerators

• Does clock-gated weight-stationary scheduling still beat output-stationary on a second open process, with that process's own SRAM?Second-node verdict for clock-gated register-file weight-stationary scheduling from IHP SG13G2 liberty files (idle flop 34 fJ, clock gate 0.75 of a flop, ten SRAM macros with separate read energies): one gate per accumulator makes WS beat OS in all 120 cells, but ungated WS also wins 33 of 60 packed cells because IHP's SRAM costs 72 to 497 flop-cycles per weight against SKY130's 18 to 62. Library values, not measurements.
• Does the accumulator-read bug found in accel-gatedmux also inflate accel-planebatch's weight-stationary area?Does accel-gatedmux's accumulator-read bug also inflate accel-planebatch's WS area? No: the rewritten engine is bit-exact with identical counts and its area is within -3 % to +12 % with no trend (WS/OS 1.62 vs 1.66 at B = 4); the earlier verdict stands.
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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.