_gpu_bm_boot_gate.nx

_gpu_bm_boot_gate.nx -- BARE-METAL SOVEREIGN-GPU rung BM-GPU-3: GPU bring-up over the BAR0 MMIO register file. A sovereign driver does the nouveau-style nvkm boot sequence against a spec-faithful BAR0 register MODEL: 1. read NV_PMC_BOOT_0 @0x000000 -> chip id; decode chipset+arch family (Blackwell GB20x ~0x1B0). A read of ALL-1s (0xFFFFFFFF) = the GPU fell off the bus (real nouveau liveness check) -> dead. 2. read NV_PTIMER_TIME_0 @0x009400 twice -> the ns clock must ADVANCE (GPU core clock alive). 3. read VRAM size @0x100000 (PFB) -> 16384 MiB (16 GiB, the 5080; cf. R4b measured ~14.88GiB usable). 4. write NV_PMC_ENABLE @0x000200 (turn engines on) -> read-back latches (engines enabled). NISHI-ECOSYSTEM-ONLY: our model + our driver; the NV register map is the last-mile hardware spec (open-gpu- kernel-modules / nouveau). HONEST SCOPE: bring-up LOGIC vs a spec-faithful model; real MMIO = BM-GPU-6 on native Linux. GREEN iff: BOOT_0 alive + chipset!=0 + arch-family==0x1B0 (Blackwell); PTIMER advances (clock alive); VRAM==16384MiB; PMC_ENABLE write read-back latches; AND tampers (BOOT_0=0xFFFFFFFF off-bus / stuck PTIMER) are correctly detected as dead. Marker -> knowledge/status/gpu_baremetal.log (BMBOOTGATE). license_tier: ORIGINAL