docs: record the ICG replacement and its evidence

Close out the chapter 3 documentation: hp-platform.md gains the ICG
section (three override points, per-PDK cell table, the ICS55 SE-into-E
note, and the two-state reset rationale), leaving only physical/STA
qualification deferred; hp-rv64-validation.md records the MEM_INTF ICG
results, the five boot testbench modes, and the four SoC-level runs with
the remaining gaps; the two READMEs extend the override inventory to
hart-ID + sysmap + SRAM wrappers + clock-gating cells.

docs/hp-rv64-validation.md

@@ -134,6 +134,23 @@ qualification. Current evidence requires, at minimum:
   to Icarus) passes on the ICS55 path as well, and the `ics55.mk` CI profile
   smoke simulation (`APP=ci_smoke`, Verilator) passes with the macro path
   compiled into the SoC.
+- The chapter 3 ICG swap is validated in simulation on all four PDKs: the
+  `gated_clk_cell.v`/`tdt_gated_clk_cell.v`/`BUFGCE.v` overrides select
+  `sg13g2_slgcp_1` (IHP130), `ICGX1H7R` (ICS55, scan enable ORed into `E`),
+  `sky130_fd_sc_hd__sdlclkp_1` (SKY130), or
+  `gf180mcu_fd_sc_mcu7t5v0__icgtp_1` (GF180; repo-owned sim model in
+  `rtl/tech/gf180_seq_sim_cells.v` because the locked checkout never ships
+  the vendor latch UDP the cell model references) under a `PDK_*` define
+  without `PDK_BEHAV`. The vendored MEM_INTF `c906_icg_test_tb` gate sequence
+  passes on all four cell paths (Icarus adaptation; the pass-through default
+  fails it by design since it never gates). The focused boot testbench passes
+  with real clock gating for all four PDKs — the IHP130/ICS55 modes run SRAM
+  macros and ICG together, the SKY130/GF180 modes run ICG with behavioral
+  SRAMs. One integration fix was required for two-state simulators:
+  `hp_core_wrapper` asserts the C906/DTM ICG scan-enable while the core is
+  held in reset, so flops behind closed gates initialize on running-clock
+  edges (the DTM sleeps at boot and otherwise holds `hartreset_n` low);
+  pass-through modes ignore the scan-enable input and stay bit-identical.
 
 `hp-linux-sim` was run with a bounded wall-clock budget this round and its
 current frontier is recorded above; the synthesis-dependent gates remain
@@ -147,17 +164,20 @@ evidence: `make CONFIG=configs/ci/ihp130-hp.mk PDK_BEHAV=NO SIMU=VERILATOR
 hp-smoke-sim` builds the whole SoC (C906 `aq_spsram_*` wrappers and
 `tc_sram`) on the IHP130 macro models and passes with
 `SIM_TEST_PASS code=0` plus the `HP_LINUX_READY`/`HP_GA2D_PASS`/
-`HP_GA2D_CACHE_CLEAN` markers. The same SoC smoke passes on the ICS55 macro
+`HP_GA2D_CACHE_CLEAN` markers; with the ICG overrides the same run also
-path (`PDK=ICS55 PDK_BEHAV=NO`, 3.64M cycles, `SIM_TEST_PASS code=0` with the
+exercises the real `sg13g2_slgcp_1` clock gates. The same SoC smoke passes on
-full GA2D cache-lifecycle marker sequence); the default 300 s
+the ICS55 macro+ICG path (`PDK=ICS55 PDK_BEHAV=NO`, 3.64M cycles,
+`SIM_TEST_PASS code=0` with the full GA2D cache-lifecycle marker sequence),
+and the `sky130.mk` and `gf180.mk` CI profile smokes (`APP=ci_smoke`,
+Verilator) pass with the `sky130_fd_sc_hd__sdlclkp_1` /
+`gf180mcu_fd_sc_mcu7t5v0__icgtp_1` ICG compiled in. The default 300 s
 `HP_SMOKE_SIM_TIME` is only enough when the run is uncontended, and the bare
 `ics55.mk` profile-default `sim` (no fast-flash) exceeds its 180 s default
-budget in this environment, so both were run with the CI-sized time budgets.
+budget in this environment, so these were run with CI-sized time budgets.
 All stay required evidence for qualification.
 
 Deferred this phase: low-power support (`core0_pad_lpmd_b` unconnected), DFT
-(scan/mbist tied off), the debug SBA AXI master (unconnected), the chapter 3
+(scan/mbist tied off), the debug SBA AXI master (unconnected), and HP Linux
-ICG (`gated_clk_cell`) replacement, and HP Linux
 re-qualification timing/performance evidence. The repo-owned OpenSBI platform
 registers `fdt_irqchip_init` (v1.9 supports the `thead,c900-plic` match with
 T-Head delegation fixups), so the C906-internal PLIC is initialized by

docs/ip/hp-platform.md

@@ -82,10 +82,38 @@ off as in `tc_sram.sv`.
 Every other configuration — including the committed `PDK_BEHAV=YES` CI
 profiles — compiles the upstream behavioral `aq_f_spsram_*` instance
 byte-identically.
+
+The chapter 3 ICG swap is implemented alongside: `gated_clk_cell.v` (the 216
+CPU clock gates), `tdt_gated_clk_cell.v` (the debug module gate), and
+`BUFGCE.v` (the PLIC/CLINT divide-by-2 gate in `aq_mp_clk_top.v`) have
+reviewed overrides in `rtl/mini/ip_overrides/`. With a PDK define and without
+`PDK_BEHAV` — no `HAVE_SRAM_MACRO` knob, the ICG is a base cell — each
+override instantiates the process clock-gating cell:
+
+| PDK | ICG cell | Enable/scan mapping |
+| --- | --- | --- |
+| IHP130 | `sg13g2_slgcp_1` | `GATE`=enable, `SCE`=scan enable |
+| ICS55 | `ICGX1H7R` | no test-enable pin: scan enable ORed into `E` |
+| SKY130 | `sky130_fd_sc_hd__sdlclkp_1` | `GATE`=enable, `SCE`=scan enable |
+| GF180 | `gf180mcu_fd_sc_mcu7t5v0__icgtp_1` | `E`=enable, `TE`=scan enable |
+
+`BUFGCE` has no scan enable upstream, so SCE/TE tie off there. The GF180
+vendor model cannot elaborate (its UDP latch primitive is not shipped in the
+locked checkout), so its simulation model is repo-owned in
+`rtl/tech/gf180_seq_sim_cells.v`, following the existing `dffq` precedent.
+Because two-state simulators only apply an async-reset flop's reset value on
+a real reset edge, `hp_core_wrapper` asserts `pad_yy_icg_scan_en`/
+`pad_tdt_icg_scan_en` while the core/DTM is held in reset, keeping the gated
+clocks transparent so flops behind closed gates initialize (the DTM sleeps at
+boot and would otherwise hold `hartreset_n` low forever). `PDK_BEHAV` and
+PDK-less builds keep the upstream defaults byte-identical (pass-through for
+the two `*_gated_clk_cell`, the behavioral latch gate for `BUFGCE`), and
+pass-through ignores the scan-enable input entirely.
 Deferred this phase: low-power support
 (`core0_pad_lpmd_b` unconnected), DFT (scan/mbist tied off), the debug SBA AXI
-master (unconnected), the chapter 3 ICG (`gated_clk_cell`) replacement,
+master (unconnected),
-physical/LEC qualification of the macro path (synthesis mapping, STA), and
+physical/LEC qualification of the macro and ICG paths (synthesis mapping,
+STA), and
 HP Linux re-qualification timing/performance evidence.
 
 ### Boot bundle V2

rtl/README.md

@@ -19,11 +19,15 @@ SYSCTRL lifecycle signals. `make setup-openc906` (part of `make setup`)
 restores the locked checkout and `make openc906-prepare` emits the generated
 filelist and manifest below `build/<variant>/generated/openc906/`; the OpenC906
 sources are an external lint boundary. The reviewed hart-ID, sysmap
-address-attribute, and SRAM wrapper overrides live in `rtl/mini/ip_overrides/`
+address-attribute, SRAM wrapper, and clock-gate (ICG) overrides live in
+`rtl/mini/ip_overrides/`
 (the `aq_spsram_*.v` overrides implement the integration manual chapter 3
 memory swap and select IHP130 `RM_IHPSG13_1P_*` or exact-geometry ICS55
 `ics55_ecos_sram_*` macros only under `PDK_IHP130`/`PDK_ICS55` +
-`HAVE_SRAM_MACRO` without `PDK_BEHAV`) and are applied
+`HAVE_SRAM_MACRO` without `PDK_BEHAV`; the `gated_clk_cell.v`,
+`tdt_gated_clk_cell.v`, and `BUFGCE.v` overrides implement the chapter 3 ICG
+swap and select the process clock-gating cell under a `PDK_*` define without
+`PDK_BEHAV`) and are applied
 by filelist generation, never by editing the vendored checkout. The former
 VexiiRiscv HP generator is preserved
 only as the frozen Std-series asset (`make std-vexii-generate`). See

scripts/README.md

@@ -130,10 +130,12 @@ source used by Mini product profiles and verifies the checked-out revision;
 the vendored checkout is never modified. `generate_openc906.py` resolves the
 upstream `C906_RTL_FACTORY/gen_rtl` filelists from that checkout, substitutes
 the reviewed overrides from `rtl/mini/ip_overrides/` (the hart-1
-`aq_sysio_kid.v`, the strong-order MMIO-window `sysmap.h`, and the eight
+`aq_sysio_kid.v`, the strong-order MMIO-window `sysmap.h`, the eight
 `aq_spsram_*.v` SRAM wrappers whose PDK-selectable macro path — stacked
 IHP130 `RM_IHPSG13_1P_*` or exact-geometry ICS55 `ics55_ecos_sram_*` — is
-gated on `PDK_IHP130`/`PDK_ICS55`+`HAVE_SRAM_MACRO` without `PDK_BEHAV`,
+gated on `PDK_IHP130`/`PDK_ICS55`+`HAVE_SRAM_MACRO` without `PDK_BEHAV`, and
+the `gated_clk_cell.v`/`tdt_gated_clk_cell.v`/`BUFGCE.v` clock-gate overrides
+that select the process ICG cell under a `PDK_*` define without `PDK_BEHAV`),
 each pinned to
 the upstream file's SHA-256 so a locked-revision move forces review), and
 emits the single compilation unit `openc906_combined.v` below `build/`;