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Introduction

The AMD BC-250 hardware

The board, the APU, its specs and its known hardware flaws.

The AMD BC-250 is a compact board based on a semi-custom APU codenamed Oberon for the CPU and Cyan Skillfish for the graphics — the same silicon family as AMD’s current-generation consoles. It was produced for mining systems (typically mounted several boards per chassis) and today shows up on the second-hand market at low prices.

Key specifications

ComponentDetail
CPU6 cores / 12 threads Zen 2 (“Oberon”), up to 3.9 GHz (Turbo), 4.0 GHz validated
GPURDNA 2 “Cyan Skillfish” (gfx1013), up to 40 Compute Units unlockable
Memory16 GB GDDR6 shared (UMA) between CPU and GPU
Compute~11.3 TFLOPS FP32 at 40 CU / 2000 MHz (measured with vkpeak)
Memory bandwidth~350–367 GB/s (measured with clpeak)
Video output1× DisplayPort

Memory is unified: the GDDR6 is shared between system and graphics. By default about 8 GB is assigned as VRAM, but on Linux the video space can be extended via the GTT (Graphics Translation Table), letting Vulkan see ~13 GiB of memory — especially useful for AI models.

Unlocking the 40 CUs

The GPU has 40 CUs but the driver enables only 24 by default. SkillFishOS routes them up to 40 live (no reboot): it boots at the driver baseline and a service brings it to 40 at startup, adjustable from the Tuner. The reverse-engineering of the unlock is documented by bc250-40cu-unlock; the runtime control via umr is inspired by bc250-cu-live-manager (clean-room reimplementation).

With 40 CUs active, SkillFishOS measures 11385 GFLOPS FP32 (vkpeak) from cold, versus ~6141 for a baseline 24-CU configuration: about +85%.

Hardware flaws to know about

The BC-250 is repurposed “mining” hardware: it has some limitations that SkillFishOS works around in software. Knowing them explains many of the system’s choices.

Broken DisplayPort Hot-Plug Detect (HPD)

The monitor connection detection on the DisplayPort connector does not work: the board doesn’t “see” when you plug in a screen. SkillFishOS solves this with a dedicated daemon (skillfish-dp-hotswap) that forces detection at boot and watches for monitor changes at runtime, plus the video=DP-1:e kernel parameter as a fallback. See Desktop and Troubleshooting.

Broken ACPI suspend

Suspend (s2idle is broken): the board goes to sleep but does not wake up and needs a reset. A suspended machine is also unreachable remotely. For this reason SkillFishOS permanently disables all sleep states (see Desktop). It is a mandatory measure.

IOMMU unusable

The IOMMU on the BC-250 is unstable: it must never be enabled. The system always boots without IOMMU.

Thermal sensors

Only the GPU edge temperature sensor is available; there is no VRAM temperature sensor. The stock cooling is marginal, so back-to-back benchmark comparisons are invalid (heat-soak effect): let the board cool down for a few minutes between runs.

Cooling, 3D-printable cases and fans

The BC-250 arrives bare, designed for mining racks with five 80 mm screamer fans driven by the power-distribution connector. Desktop use needs dedicated cooling. Two things must be cooled: the APU heatsink and the GDDR6 chips, which run very hot and have no temperature sensor (see GPU/overclock).

What works (community advice):

  • 2× 120 mm static-pressure fans aimed at the heatsink are the most common desktop setup; with no case you can lay them directly on top of the heatsink (zip-ties through the fins).
  • A dedicated VRAM fan is strongly recommended if you overclock: the GDDR6 modules are the hottest spot.
  • The fan connects to the board’s 4-pin PWM header — SkillFishOS drives it via nct6686 (sensors) and keeps it on auto.

Cases and ducts (free STL, 3D-printable):

ModelAuthorNotes
Console Style CaseArthrimus”Console” case + PSU bay, shroud for 1× 120 mm
ASRock BC-250 Shell CaseonemorecapSnap-on shell, quick single-fan mount
Yet Another BC-250 Fan ShroudViRazY140 mm intake + 120 mm exhaust
Case ATX PSU & Fan DuctZMASLOUses a standard ATX PSU, duct that won’t damage the cooler
Standard ATX PSU caseCatSiewDaiFull case for ATX power supplies
OC vRAM Fan Kit (remix)marccyberwizFan kit dedicated to the VRAM for overclocking
NexGen3D — DIY Steam Machine (Bazzite)NexGen3DFull Steam Machine-style case for the BC-250
NexGen3D — Steam Machine PRO (liquid-cooled)NexGen3DLiquid-cooled PRO (AIO) version — maximum cooling
NexGen3D — AIO mount for BC-250NexGen3DBracket to mount an AIO (liquid cooler) on the BC-250

Reference cooling guide: Cooling Solutions — amd-bc250-docs.

Sources