Matching PCIe audio latency over standard Ethernet

Low-latency audio on Linux usually means choosing between the bus jitter of USB class drivers and the physical constraints of an internal PCIe card. The eth68 sidesteps that choice by running bare-metal firmware on an STM32H7 microcontroller that emulates a netJACK1 master endpoint over standard Ethernet. In loopback tests at 48 kHz with a 64-sample buffer, it clocks 3.62 milliseconds of round-trip latency, matching an RME HDSPe PCIe card without requiring specialized AVB switches or proprietary network protocols.

Scaling channels over Ethernet usually compounds latency, but the hardware design here separates clock distribution from packet delivery. Units share a master high-frequency clock over daisy-chained BNC cables to eliminate drift, while a broadcast UDP sync command resets direct memory access transfers to align buffers within a single sample. Under an oscilloscope, two synchronized units align analog waveforms to less than one microsecond while preserving single-unit latency.

What stands out is the hardware visibility. Instead of burying buffer health in driver logs, the rear panel includes a dedicated digital monitoring pin. Connecting an oscilloscope to that pin measures the exact duration the host computer takes to process each audio cycle, displaying scheduling jitter directly against the 1.33 millisecond deadline. For Linux pro audio, which has spent years caught between internal PCIe cards and proprietary network protocols, this kind of open, deterministic hardware shows how standard Ethernet can become a reliable foundation for modular professional setups.