retroSoC/docs/hp-rv64-validation.md

HP RV64 Migration Validation

The active contract is HP platform. LP remains RV32 Hazard3 (hart 0); HP is the locked, pre-generated T-Head OpenC906 (hart 1, RV64GC with Zicsr/Zifencei, M/S/U modes, Sv39, 32-bit SoC physical addresses). No upstream CPU or RT-Thread source is modified.

Current status after the OpenC906 core swap

All simulation evidence below was gathered with the previous generated VexiiRiscv HP core and is historical: it must not be presented as OpenC906 qualification. Current evidence requires, at minimum:

• make setup-openc906 (part of make setup) restoring the locked openc906 checkout, and make openc906-prepare emitting build/<variant>/generated/openc906/openc906.fl and its manifest under the pinned upstream sha256 guard, with the reviewed rtl/mini/ip_overrides/aq_sysio_kid.v hart-ID override applied by filelist generation rather than by editing the vendored checkout.
• Verilator compile of the OpenC906 HP subsystem, including the serializing axi4_downsizer_128to64 and axi4_mmio_demux path.
• Fresh hp-smoke-sim, hp-rtthread-sim, and hp-linux-sim runs from their committed IHP130 profiles with all contract markers and SIM_TEST_PASS code=0, exercising the internal C906 CLINT/PLIC and the time-CSR mtime delivery.
• The IHP130 behavioral PR regression on the swapped design.

OpenC906 evidence gathered (2026-10-10)

• hp-smoke-sim on configs/ci/ihp130-hp.mk (Verilator): HP_LINUX_READY, HP_GA2D_PASS, HP_GA2D_CACHE_CLEAN, SIM_TEST_PASS code=0; 3,629,906 cycles in 285 s. This exercises C906 boot at 0x38000000, the 128-to-64 downsizer and MMIO demux, the mailbox protocol, the GA2D engine through the HP data path, and the T-Head dcache.cva/dcache.iva cache lifecycle handshake.
• hp-rtthread-sim on configs/ci/ihp130-rtthread.mk (Verilator): all selftest markers (RTTHREAD_RV64_PASS, RTTHREAD_TIMEOUT_PASS, RTTHREAD_PREEMPT_PASS, RTTHREAD_CONTEXT_PASS, RTTHREAD_IPC_PASS, RTTHREAD_MAILBOX_IRQ_PASS, RTTHREAD_TEST_PASS) plus HP_RTTHREAD_PASS and SIM_TEST_PASS code=0; 6,373,952 cycles in 542 s. This exercises the C906 internal CLINT timer tick and MSIP IPI, the internal PLIC mailbox doorbell (MEIP), and the full cached SDRAM fill path.
• hp-linux-sim on configs/ci/ihp130-hp.mk (Verilator, bounded 2 h wall, 83.5 M emulator cycles / 41.8 M HP cycles): OpenSBI v1.9 completes fully on the C906 with the repo-owned platform (custom timer device reading the time CSR plus internal-CLINT MSWI IPI, custom UART1 console), and fw_jump hands off to the kernel Image at 0x38400000 with the DTB at 0x38080000 (bundle segments byte-identical to the built images, CRC-checked). The kernel enters S-mode, brings Sv39 up, executes past set_cpu_online()'s first AMO, and prints Linux version 6.12.105+ on the SBI console: the earlier boot blocker is fixed (see the MAEE entry below). A longer bounded run (8 h wall) with the STIMECMP fix additionally boots the kernel through console init, BogoMIPS calibration, devtmpfs, and the switch to the riscv_clocksource with a healthy periodic tick; userspace acceptance (HP_LINUX_READY) evidence is collected on that run. The target stays unqualified until that acceptance completes.
• The Linux boot blocker was a doc/RTL mismatch in OpenC906, root-caused with bare-metal MMU payloads and locked by simulation evidence: the user manual states mxstatus.MAEE resets to 0, but the RTL (aq_cp0_ext_csr.v) resets it to 1. With MAEE set, S-mode page attributes come from the T-Head extended PTE bits [63:59], which a stock mainline kernel never programs, so every translated page is non-cacheable; the C906 then raises a store/AMO access fault (cause 7) for any AMO on such a page (aq_lsu_ag.v: !mmu_ca && ag_pipe_amo). The first victim is set_cpu_online()'s amoor.d.aqrl on __cpu_online_mask, after which the kernel enters the do_trap_break storm. Loads/stores and full Sv39 page-table walks (4 KiB three-level, 2 MiB megapage, high-half canonical VAs, cold fills from SDRAM after D$ eviction) were proven correct independently: the failure was purely the AMO-on-non-cacheable rule. The OpenSBI platform early_init now clears mxstatus.MAEE (app/ports/linux/opensbi/retrosoc_hp/platform.c), making translated accesses follow the sysmap override (RAM cacheable, MMIO strong-order device) so the stock kernel needs no T-Head PBMT errata. A directed payload then passes the full AMO battery (amoor/amoadd/amoswap/ lr-sc, cold-line and high-half-VA variants).
• The post-sched_clock stall was a second doc/RTL trap of the same family: the C906 ORs the internal CLINT's hardware supervisor-timer line into mip.STIP (aq_cp0_trap_csr.v: st_int && CLINTEE || stip_reg) and the RTL resets CLINTEE to 1. Nobody parked the internal STIMECMP, and the compare registers' 0xFFFF_FFFF reset values are not guaranteed to be applied (the HP hold-reset produces no async negedge in Verilator, leaving them at zero), so the hardware S-timer line fired continuously: the first sie.STIE enable in the kernel's time_init dropped it into an infinite supervisor-timer storm and starved the boot thread. M-mode firmware (RT-Thread, OpenSBI) is immune, which is why earlier targets were unaffected. The OpenSBI early_init now parks both internal-CLINT compare registers at cold boot, making the state deterministic on silicon and in simulation; probe evidence shows MTIMECMP armed exactly one jiffy out and MTIP firing exactly at the compare value on a healthy 288 kHz-cycle cadence.
• The RT-Thread bring-up exposed and fixed three latent issues, each locked by directed regression. (a) The C906 resets with caches and the BPU disabled and does not initialize the cache/predictor RAMs: HP payloads must run the upstream mcor invalidate-then-mhcr enable sequence (app/ports/rtthread/start.S, OpenSBI early_init). Without it the 1 kHz tick ISR livelocked the uncached core, and enabling caches without invalidating first produced wild control flow. (b) sdram_axi4 computed WRAP wrap-back addresses from the decrementing remaining-beat count, corrupting every cache-line fill starting mid-line (locked by WRAP cases in tests/rtl/sdram_data_tb.sv). (c) The data crossbar's burst_legal computed a WRAP burst's last address as if it were INCR, faulting fills that start in the last 64 bytes of a 4 KiB page (locked by the page-edge case in tests/rtl/axi4_data_crossbar_tb.sv). No previous master issued WRAP bursts, so (b) and (c) predated the swap.
• Focused hp_c906_boot_tb (pytest test_hp_platform.py): the real smoke payload runs on hp_core_wrapper plus the production MMIO chain (64-to-32 downsizer, address gate, HP-to-LP CDC bridge) and completes the full mailbox/GA2D-phase protocol.
• The swap exposed and fixed a latent integration bug: the merged HP port initially inherited the read-only I-cache slot's zero write credits in the data crossbar; axi4_data_crossbar.sv now grants the HP slot two write credits, locked by a new write/readback case in ga2d_platform_tb.
• The sysmap override is required for correctness: the upstream default marks the Mini MMIO window cacheable/bufferable, which absorbs device writes in the C906 store buffer; rtl/mini/ip_overrides/sysmap.h marks the MMIO and core-internal CLINT/PLIC windows strong-order non-cacheable per the user manual.
• The integration manual chapter 3 SRAM swap is validated in simulation: the eight rtl/mini/ip_overrides/aq_spsram_*.v overrides select IHP130 RM_IHPSG13_1P_* macro combinations under PDK_IHP130+HAVE_SRAM_MACRO without PDK_BEHAV, and the focused boot testbench variant test_c906_boots_smoke_payload_with_ihp130_sram_macros boots the real smoke payload (cache maintenance plus GA2D data movement, which exercises the BHT/ICache/DCache/JTLB RAMs for real) on the macro path with the same HP_C906_BOOT_TEST_PASS verdict as the behavioral run.

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 unrun (synthesis, netlist simulation, STA, and the physical/LEC qualification of the macro path). The SoC-level macro-mode simulation now has passing 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. 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 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 OpenSBI before the kernel probes it; the minimal Linux acceptance uses the hvc0 console, the SBI TIME timer, and the polled mailbox path.

Historical VexiiRiscv evidence (pre-swap)

Reproduction (VexiiRiscv)

make setup-vexiiriscv setup-hp-rtthread setup-hp-linux
make CONFIG=configs/ci/ihp130-hp.mk SIMU=VERILATOR hp-smoke-sim
make CONFIG=configs/ci/ihp130-rtthread.mk SIMU=VERILATOR hp-rtthread-sim
make CONFIG=configs/ci/ihp130-hp.mk SIMU=VERILATOR hp-linux-sim
python3 scripts/regress.py --root . --suite pr --pdk IHP130 --behavioral-only

HP_CROSS is independent of LP CROSS and resolves to the compiler in the dependency lock. RT-Thread is official v5.3.0 at 99428a1e7f7447955aa860f7c969273a12095b8f, compiled with RV64 lp64d. Its selftest qualifies integer contexts; it does not qualify FCSR preservation or floating-point tasks. Linux uses its Buildroot RV64 Linux compiler, Sv39, static musl/BusyBox and a small uncompressed CPIO with a dedicated /init.

V2 flash bundles discriminate Linux (1, four entries), smoke (2, one executable) and RT-Thread (3, one executable). Rebuild V1 bundles. The loader checks strict flags, workload/count/types, fixed addresses, bounds, non-overlap, unused slots and CRC. In ordinary builds only smoke enters the GA2D/cache lifecycle protocol. LP alone owns the final SYSCTRL TEST_STATUS write for all workloads.

The private NPU-P6 acceptance build reuses workload 1's four-entry transport so the frozen corpus shard occupies the existing Image slot. Its compile-time RS_NPU_P6_ACCEPTANCE path deliberately continues beyond the Linux-ready checkpoint into the same GA2D/cache lifecycle protocol; an ordinary Linux build still terminates at Linux-ready. This does not add a workload number or change the V2 header ABI.

The ihp130-apu evidence profile likewise uses workload 1 only as the existing four-entry transport. Its application-specific apu_release LP loader owns the APU acceptance semantics; that bundle label does not claim a Linux boot result.

Measured runs (VexiiRiscv)

Initial RV64 validation uses configs/ci/ihp130-hp.mk and BUILD_TIMESTAMP=2026-09-25-11-42, producing build/ihp130-hp-2026-09-25-11-42-bb2e93b39338/.

Run	Result	Evidence below variant
RV64 generated core and Verilator compile	Pass	generated/vexiiriscv/manifest.json, sim/verilator/result-compile.json
GA2D/cache lifecycle smoke	SIM_TEST_PASS code=0, 3,446,054 cycles, 191 seconds	sim/verilator/sim.log, result-hp-smoke-sim-check.json in the same directory
RT-Thread kernel/platform	All required markers and SIM_TEST_PASS code=0, 6,412,946 cycles, 360 seconds	sim/verilator/hp-rtthread/sim.log, result-sim-check.json

The final dedicated configs/ci/ihp130-rtthread.mk profile passed all markers and TEST_STATUS at 6,395,372 cycles in 357 seconds, using BUILD_TIMESTAMP=2026-09-25-12-18. Its evidence is build/ihp130-rtthread-2026-09-25-12-18-bb2e93b39338/sim/verilator/hp-rtthread/. The final context probe compares registers against an original 64-bit sentinel stored on each task's stack, catching identical truncation of multiple registers. The final smoke also passed at 3,460,934 cycles in 195 seconds, with evidence in sim/verilator/hp-smoke/ under the initial variant.

Linux Image is 2,152,448 bytes; the static, uncompressed CPIO is 302,080 bytes. BusyBox is expanded from allnoconfig and an explicit allowlist; effective options and static ELF linkage are checked. Linux acceptance is still running without an emulator wall-clock timeout; no Linux pass is claimed yet. New workload runs write logs to sim/verilator/hp-{smoke,rtthread,linux}/. Structured results start as running; failures/interruption replace old passes. A UART banner is diagnostic, never the final verdict.

The affected Python and publication bindings pass 177 tests; one PDF-inspection test is skipped because pypdf is not installed. C format, C policy and host tests, Ruff, dependency-lock validation, setup-hp-rtthread and the dedicated profile's Verilator doctor pass. The final publication-focused run passes 193 tests with one missing-pypdf skip. The full Python run reports 974 passed and 5 skipped; its two missing-FLAC-corpus failures were resolved by installing the checksum-locked corpus and rerunning both tests (2 passed). Thus 976 cases have passing evidence. The other skips are optional P7 model/MFCC inputs; no test expectation was weakened to hide a missing input. After the firmware-reservation correction, all 62 affected platform and publication checks pass.

The IHP130 behavioral PR regression completed successfully with BUILD_TIMESTAMP=2026-09-25-12-14: strict lint, firmware builds, Verilator ci_smoke (6,783,746 cycles, 384 seconds), DEBUG_GDB_PASS, and Icarus SIM_TEST_PASS. Artifacts use build/ihp130-2026-09-25-12-14-* and build/ihp130-debug-2026-09-25-12-14-*. Warning-baseline comparisons report new/increased signatures as non-blocking observations; baselines were not modified. No synthesis or STA result is implied by this regression.

RT-Thread first-schedule failure and correction

The first BSP run reached HP_RTTHREAD_BOOT and then reported RTTHREAD_TRAP cause=1 epc=deadbeee, failure 92, followed by LP failure 18. Evidence is retained in sim/verilator/hp-rtthread-idle-stack-failure/ under the initial variant. This was a BSP integration error:

1. The BSP used RT_IDLE_THREAD_STACK_SIZE; the locked upstream src/idle.c reads IDLE_THREAD_STACK_SIZE and otherwise selects 128 bytes without heap.
2. The failing ELF's idle_thread_stack was 128 bytes at 0x38004530. Upstream rt_hw_stack_init reserves 512 bytes for 32 RV64 integer slots and 32 double-precision slots, filling them with 0xdeadbeef.
3. That frame starts at 0x380043b0, 384 bytes before the allocated stack, overwriting _object_container, interrupt-switch state, the scheduler's ready bitmap and other globals. This explains the invalid first-schedule state and is independent of the AXI crossbar.
4. The BSP now uses the correct macro with 2048 bytes and a compile-time lower bound. The same integrated test then passed scheduling, RV64 context, IPC, timer timeout, and mailbox IRQ checks. Vendor source stayed unchanged.

Linux firmware reservation correction

The first RV64 run reached Linux 6.12.105 and memory initialization. Its log reported no /reserved-memory node and included the full SDRAM range beginning at 0x38000000. OpenSBI's preceding PMP report protected its resident code/data from S-mode. Static inspection confirmed that the custom platform has no generic fdt_fixups() final-init hook; Linux arch/riscv/mm/init.c:setup_bootmem reserves the kernel, initrd, DTB and DT-declared regions, not an implicit firmware window. Thus the DT omitted a live firmware allocation. No resulting crash was observed; the run was deliberately interrupted to correct this integration defect.

The retained log is sim/verilator/hp-linux-before-firmware-reservation/ under the initial variant. The DT now reserves the complete, already allocated 512 KiB OpenSBI window with no-map, and the effective-config guard requires CONFIG_OF_RESERVED_MEM=y. The DTB test checks both the exact range and no-map. The corrected runtime now prints 0x0000000038000000..0x000000003807ffff (512 KiB) nomap non-reusable opensbi@38000000, confirming that Linux consumed the reservation. Userspace acceptance is still in progress.

During the subsequent quiet Initmem setup node 0 interval, two read-only host debugger samples captured 64,772,063 and 66,503,381 emulator cycles. The sampled Sv39 PCs resolve to __init_single_page and memmap_init_range in the actual vmlinux; disassembly passes s0 as the PFN and increments it at loop end. s0 advanced from 0x3b0c4 to 0x3b6ed, toward the s1=0x3c000 bound. Privilege remained S-mode and SATP mode was 8. This establishes loop progress during that interval, not a complete boot verdict. Samples and disassembly are retained under meta/hp-rv64-validation/; no DUT state was written. Later samples at 84,162,019 and 92,239,597 cycles resolve to should_skip_region / __next_mem_range and __free_pages_ok called by memblock_free_all, respectively. A further sample at 97,866,745 cycles is in __free_pages_core, with a later page-descriptor block address. These locate the later allocator work separately from the earlier page-descriptor loop. After IRQ initialization, samples landed in timer handling. The interrupted SEPC then moved from memset to add_device_randomness; the latter frame was decoded from valid, matching-tag L1 data-cache lines and checked against the RISC-V pt_regs layout. UART subsequently reported the 9-bit ASID allocator. These observations avoid treating an IRQ-handler PC or stale raw SDRAM as evidence of main-thread progress.

Coverage limits

The repository's mechanical C format/policy checks are partial MISRA evidence; no complete MISRA certification or new approved Required-rule deviation is claimed. Board MMIO uses fixed, naturally aligned 32-bit accesses to declared register windows; RV64 pointer width does not widen device accesses.

Synthesis, netlist simulation, STA and synthesis-dependent metrics are deferred by explicit user instruction. PPA, CDC/RDC, physical SRAM mapping, hardware board runs and silicon qualification are not established by these simulations. The behavioral evidence is IHP130-specific; other PDK matrices and extended nightly benchmarking were not rerun in this migration. The GDB regression exercises LP Hazard3 debug; it is not independent RV64 HP debug/JTAG qualification. The minimal Linux configuration leaves CONFIG_RISCV_ISA_ZICBOM disabled. The custom OpenSBI platform does not import Zicbom into its hart-extension mask, so it leaves MENVCFG CBIE/CBCFE disabled. The cache-maintenance evidence here is the M-mode smoke; enabling native Linux non-coherent DMA requires the matching firmware extension/permission setup and a separate S-mode CBO acceptance test. Publication source bindings are updated separately from the previously reviewed PDF snapshot; a fresh PDF requires an explicitly reviewed committed snapshot.