USB Audio Interface causing a ton of ISR count in LatencyMon

Analyzing High ISR Counts Caused by USB Audio Interface on ASUS TUF B550-Plus Motherboard

Experiencing latency or system performance issues when connecting audio interfaces can be challenging, especially when troubleshooting hardware and driver conflicts. Recently, some users have reported unusually high interrupt service routine (ISR) counts when connecting certain USB audio devices, which can significantly impact system responsiveness.

Case Overview

A user utilizing an Audient EVO 4 USB audio interface on an ASUS TUF B550-Plus motherboard paired with a Ryzen 7 5800X CPU observed a notable increase in ISR activity upon connecting the interface. Latency monitoring tools, such as LatencyMon, indicated a spike of approximately 1500 ISRs per second, which is indicative of potential driver or hardware bottlenecks.

System Details:

• Motherboard: ASUS TUF B550-Plus
• CPU: AMD Ryzen 7 5800X
• Audio Interface: Audient EVO 4
• Issue: Significant ISR spike upon connecting the USB audio device

Troubleshooting Observations

In the absence of the USB audio interface, system performance appears normal, with typical ISR counts. However, once plugged in, the system experiences a surge in interrupt routines, suggesting that the interface or its drivers are causing excessive interrupt activity—likely due to USB controller limitations or conflicts.

Known Issues with B550 Motherboards

The AMD B550 chipset series is documented to have some USB stability issues, including USB dropout and connectivity problems. These issues are often related to the motherboard’s USB controller handling or driver support, which can lead to elevated system interrupts when bandwidth or hardware resources are constrained.

Potential Solutions and Recommendations

1. Upgrade USB Hardware Infrastructure
2. Use a Powered USB Hub: Connecting the audio interface through an externally powered USB hub can offload some of the USB traffic from the motherboard’s native controller, potentially reducing ISR activity.

3. Add a PCIe USB Expansion Card: Installing a dedicated PCIe USB 3.0 or USB 3.1 expansion card can provide a more robust and isolated connection, alleviating workload on the onboard controllers.

4. Update Drivers and Firmware

5. Ensure that the motherboard’s chipset drivers and the audio interface drivers are up to date.

6. Check for BIOS updates for the ASUS TUF B550-Plus that may improve USB stability.

7. Optimize System Settings

8. Disable USB selective suspend or other power-saving features in Windows.