Replace poly_mul_sync's two 256x12 LUT register arrays (mem_A/mem_B, ~8k LUT)
with four sd_bram banks (A_even/A_odd/B_even/B_odd, 128x12). The base-case
reads mem[2k] and mem[2k+1] together, so an even/odd split gives each bank a
single read port. This removes the multi-port LUT mux and the long
BRAM->register-file route that was the mlkem_clk critical path.
sd_bram reads are synchronous (1-cycle); the existing 2-cycle issue cadence
absorbs it (address on the gap cycle, data on the issue cycle), with a
one-cycle priming gap at LOAD->RUN. Interface and behavior unchanged.
Verified byte-exact vs NIST KAT: poly_mul standalone TB 11/11, Encaps 9/9,
Decaps 9/9 (incl. reject + DECOMP), KeyGen, hello_world e2e — all PASS.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Double-buffer poly_mul_sync so the next MAC term's 256-cycle load overlaps
the current term's accumulate. Decouple the top-level MAC load index (u_ldj)
from the accumulate index (u_j) in the shared ENC_U/ENC_V/DEC_W engine; load
reads bank_a/bank_se while accumulate reads bank_t (disjoint ports, no
conflict). Accumulate stays strictly serial (psum order-dependent); only the
load is hidden.
Verified byte-exact vs NIST KAT in ~/Dev/mlkem: Encaps 9/9, Decaps 9/9
(incl. implicit-reject + DECOMP), KeyGen all, hello_world end-to-end.
ENC_U 5585->5073, ENC_V 2793->2537 (K=2). Larger relative win at K=4
(K^2 terms). poly_mul contract unchanged (standalone TB 11/11).
Wrap mlkem_top in an AXI4 burst slave (mlkem_axi_slave) mapped to the
freed FFT slot 6 at 0x1f400000 (virtual 0xbf400000). The core runs on
sys_clk/2 (25 MHz); the wrapper handles the clock-domain crossing:
start toggle->pulse, wait-stated byte-preload handshake, busy/done
sync, and direct readback taps (ek/dk/ct/ss). CPU drives it via a
register map (CTRL/STATUS/CONFIG, d/z/msg, preload + readback windows).
Wire into soc_top on the existing axiOut_6 nets (no crossbar change),
add mlkem_intr on intrpt[3]. Add sdk mlkem_test example running a
KeyGen->Encaps->Decaps self-consistency round trip.
