The ASUS Gaming Laptop ACPI Firmware Bug: A Deep Technical Investigation Overview This investigation analyzes persistent latency and stuttering issues observed on high-end ASUS ROG laptops (Strix, Scar, Zephyrus series) equipped with RTX 30/40 GPUs and Intel processors. Despite powerful hardware, users experience audio crackles, input lag, and freezing during simple tasks like video playback or Discord calls. Common Symptom Patterns High ACPI.sys Deferred Procedure Call (DPC) latency. Latency mostly concentrated on CPU 0, with prolonged interrupt processing. Periodic latency spikes every 30-60 seconds. Power cycling attempts of discrete GPU (dGPU) despite being in MUX (Ultimate) mode. Firmware-level issue, unaffected by OS reinstall or driver updates. Key Tools Used LatencyMon: Revealed ACPI.sys as main interrupt latency source. Event Tracing for Windows (ETW): For detailed tracing of ACPI events, highlighting problematic General Purpose Events (GPEs). Windows Performance Analyzer: Shows spiking latency tied to interrupt events. ACPI Table Extraction & Decompilation: Used acpidump and iasl toolsets to analyze firmware ACPI tables and Embedded Controller (EC) AML code. --- Root Causes Identified Flawed Interrupt Handler Implementation (GPE.L02 -> ECLV) The L02 GPE handler in AML calls method ECLV. It's a level-triggered interrupt firing continuously while active. The ECLV method improperly sleeps inside the interrupt context, with Sleep(100ms) and Sleep(25ms) calls. Causes blocking of CPU 0 for milliseconds, preventing timely hardware interrupt servicing and system timer updates. Also, the interrupt is artificially re-armed indefinitely via EEV0 = 0xFF when the event queue appears empty, creating a periodic timer instead of responding to real hardware events. Unconditional GPU Power Cycling Despite MUX Mode ASUS laptops support a MUX switch with two modes: Optimus mode: Integrated GPU active; discrete GPU powered on demand and routed through iGPU. Ultimate (MUX) mode: Discrete GPU physically wired directly to displays; integrated GPU powered off. Correct firmware logic (BRTN brightness method) uses HGMD flag: HGMD == 0x03 means Ultimate/MUX mode. Conditional commands are correctly routed only to active GPU. Critical flaw: Power cycling commands (e.g., LGPA method case 0x18) do not check HGMD and blindly send power-off signals to the discrete GPU even in Ultimate mode. This leads to: Attempted power-off of the only active GPU, causing display blackouts. Driver deadlocks when Windows attempts to power monitor on but driver waits indefinitely for GPU response. System crashes with BSOD (WIN32KPOWERWATCHDOGTIMEOUT). Parallel Fault in Platform Power Management DSM (PEPD device) The Device Specific Method (DSM) for power management similarly tries to cut GPU power during display-off events without MUX awareness. Shows firmware inconsistency and systemic design flaw in power management logic. --- Technical Details Summary Interrupt Latency Metrics (LatencyMon) Interrupt to process latency peaks over 65,000 µs (65 ms). ISR and DPC execution times dominated by ACPI.sys. CPU 0 spends over 90 seconds processing interrupts, other CPUs hardly affected. Periodic GPE Trigger (GPE.L02) Spikes occur every 30-60 seconds. Each GPE event lasts ~13 ms, significantly impacting real-time performance. Hardware interrupt triggers battery and AC adapter status polls, as well as GPU power state toggling. Firmware Decompiled AML Highlights GPE Handler: Defective ECLV Method:**