CHI Home Node — Pipelined DCT + Writeback/Eviction (HN-F v8)

Catalog #MC-2 (design iteration v11) · chi_hn_f_v8 · ASIL-B SEooC

The production-tier point-of-coherency + point-of-serialization for a snoopable region of an AMBA 5 CHI (Issue E-class) interconnect.

Key Features

• N_TXN (default 2) pipelined outstanding coherent-read slots, each independently sequencing lookup → snoop(s) → fill → completion, with a per-line hazard interlock stalling a new request against any active slot’s address
• Sharer-vector directory (DIR_ENTRIES=16 default, fully-associative, even parity): ReadShared adds a sharer (downgrading a unique owner via SnpShared first); ReadUnique runs a per-slot multi-snoop SnpUnique invalidate loop against every other sharer
• Direct Cache Transfer: a snooped owner’s dirty SnpRespData is forwarded straight to the requester, skipping the memory read; one per-slot buffer + SECDED codec covers both the memory- and DCT-sourced fill
• Writeback-on-downgrade (O_WB): a ReadShared downgrade of a dirty owner writes the forwarded line back to memory before completion, so a later ReadNoSnp or eviction reads a fresh copy instead of stale memory
• Eviction snoop-back (O_EVSNP/O_EVSNPW/O_EVWB): a coherent miss reclaiming a round-robin victim that is still valid and uniquely (dirty-)owned snoops that victim back and writes the recovered line to memory before the new line is fetched
• ASIL-B: config + request-address even parity (err_code 1), per-slot held-line SECDED + directory sharer-vector parity (err_code 2), SN-F read-error-to-RespErr propagation (err_code 3), outstanding-transaction watchdog (err_code 4), write-FSM complementary diverse-DMR shadow (err_code 9)
• Catalog FMEDA: SPFM 90.30%, LFM 89.44%, PMHF 3.32×10⁻⁸/h, PASS ASIL-B; verified by a golden-model coherence scoreboard (make chi_hn_f_v8), a dedicated eviction proof (make chi_evict), and formal bmc+cover (make formal_chi_hn_f_v8)

Standards & Compliance

Arm AMBA 5 CHI (Issue E); ISO 26262 ASIL-B SEooC (SPFM 90.30%, LFM 89.44%, PMHF 3.32×10⁻⁸/h)

Functional Safety

ASIL-B (SEooC) · SPFM 90.30% · LFM 89.44% · PASS

ISO 26262:2018 · FMEDA available · Safety Manual included

Register Map

Getting Started

// Minimal instantiation
chi_hn_f_v8 #(
 .ADDR_W(6)
) u_chi_hn_f_v8 (
 .clk (clk),
 .rst_n (rst_n),
 // APB4
 .p_paddr (paddr),
 .p_psel (psel),
 .p_penable (penable),
 .p_pwrite (pwrite),
 .p_pwdata (pwdata),
 .p_prdata (prdata),
 .p_pready (pready),
 // Safety
 .err_clear (1'b0),
 .err_valid (err_valid),
 .err_code (err_code)
);

Configure via the CTRL register after reset to enable the IP and set operating parameters. Monitor err_valid / err_code for any safety faults reported by the built-in safety monitor.