turing-multi-gpu-llm-server/docs/20GB_MOD_GUIDE.md

🛠️ CMP 50HX 20GB VRAM Mod & Driver Patching Guide

This guide covers how to physically mod and software-unlock the NVIDIA CMP 50HX from 10 GB to 20 GB VRAM (20,480 MiB per card), based on the validated research from xrip/cmp50hx-unlock.

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1. Hardware Modification: Swapping GDDR6 BGA Chips

Architecture & Memory Topology

• The CMP 50HX is built on the TU102 PCB with a 320-bit memory bus (10 memory pads).
• Stock Configuration: 10x 1GB (8Gbit) 14Gbps GDDR6 BGA-180 chips (e.g., Samsung K4Z80325BC-HC14).
• 20GB Configuration: 10x 2GB (16Gbit) 14Gbps/16Gbps GDDR6 BGA-180 chips:
  • Samsung: K4ZAF325BM-HC14 or K4ZAF325BM-HC16
  • Micron: D9ZCL (MT61K512M32KPA-14) / D9WCW
  • Hynix: H56G32AO8DX-004

Hardware Strapping Resistors

• After desoldering the old 8Gbit ICs and soldering the 16Gbit ICs:
• Locate the memory density strapping resistor dividers on the rear of the TU102 PCB near the memory controller.
• Move the strapping pull-up/pull-down resistor to configure the memory controller for 16Gbit per channel.

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2. The Software Barrier: NVIDIA Booter Error 0x8d

Why Stock NVIDIA Drivers Fail on 20GB CMP 50HX

• In stock closed drivers, the firmware security module (FWSEC) uses hardcoded WPR2 bounds calculated for a 10GB address space.
• On a 20GB card, stock FWSEC creates:

  WPR high:low = 04ffee00:04ffe000
  span         = 00000e00
  

• Because the hardcoded 10GB bounds do not match the 20GB span, NVIDIA Booter aborts with error 0x8d, GSP-RM fails initialization, and nvidia-smi detects no devices.

The Fix: Dynamic WPR2 Handling (xrip/cmp50hx-unlock)

• The patched NVIDIA Open Kernel Module (610.43.03) reads the FWSEC WPR2 range dynamically for each GPU's PCI BDF (Bus/Device/Function).
• It accepts span 0xe00, saves the low/high bounds per BDF, and passes GSP readiness checks.
• Mixed Cards Supported: You can run 10GB and 20GB CMP 50HX cards in the same system simultaneously because WPR2 bounds are indexed per PCI BDF.

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3. Multi-Card VRAM Scaling for LLM Inference

Cluster Setup	Total VRAM	Model Capability
2x 20GB CMP 50HX	40 GB VRAM	Runs Llama-3.3-70B or Qwen2.5-72B (Q4_K_M) across 2 slots!
3x 20GB CMP 50HX	60 GB VRAM	Runs Qwen2.5-72B (Q6_K / Q8_0) with full 64K+ context
4x 20GB CMP 50HX	80 GB VRAM	Enterprise A100-class capacity (runs 70B FP8 / Q8_0 at 128K context)