🧪 Resolved: Reducing Network Latency on LattePanda Sigma with Linux Preempt-RT

If you're using the LattePanda Sigma with a Linux preempt-rt kernel for low-latency networking applications and experiencing unexpectedly high or unstable network latency through the NICs, this guide is for you.

📌 The Problem

Users have reported significantly higher network latency (up to 450μs) on the LattePanda Sigma , even when compared to the LattePanda Mu N100 , which achieves around 40μs under similar conditions. Both devices run the same application and the NIC interrupt threads are set to real-time priority. Despite minimal CPU load, latency remains high and unstable.

🔍 Root Cause Insight

The NIC on the LattePanda Sigma is connected via PCIe , and certain power-saving features in the BIOS can introduce unpredictable delays in PCIe communication — especially in real-time environments.

After analysis by our BIOS engineering team, we identified that ASPM (Active State Power Management) and L1 Substates were enabled by default on the relevant PCIe root ports. These features are known to add latency to PCIe devices such as network cards.

🛠️ BIOS Configuration Steps to Reduce Latency

Follow these steps to disable power-saving features on the PCIe bus connected to the NIC:

1. Enter BIOS

Reboot the device and press ESC/DEL during boot to enter BIOS menu.Then press F12+INS to unlock hidden BIOS options.

2. Navigate to:

Chipset → PCH-IO Configuration → PCI Express Configuration

3. Disable ASPM and L1 Substates

Locate the following entries and disable both options:

- PCI Express Root Port 9

  * ASPM = Disabled  

  * L1 Substates = Disabled 

- PCI Express Root Port 10

  * ASPM = Disabled  

  * L1 Substates = Disabled

4. Save & Exit

Press F10 to save changes and reboot.

📈 Result

After applying the above BIOS configuration, users have seen a significant reduction in network latency, bringing it more in line with performance observed on the LattePanda Mu N100 platform.