Synchronization of Sampling in a Distributed Audio Frequency Range Data Acquisition System Utilizing Microcontrollers

Abstract

Modern distributed audio and video acquisition and processing systems utilize in-band (non-dedicated) network clock and frequency synchronization among nodes to guarantee in phase and in frequency sampling in the system, for example, AVB uses IEEE 802.1AS and Dante specifies IEEE 1588 for network clock synchronization. Synchronizing the hardware clocks of the network interfaces of the nodes of the distributed system is not sufficient in this case as the sampling process itself must be synchronized in frequency and in phase for most of the applications. For this, we need to synchronize the sampling process of A/D and D/A converters to the hardware clock of the network interface (cascade synchronization), which is typically done by tuning dedicated phase-locked loop (PLL) chips to produce the required in-frequency and in-phase clock for the converters. Unfortunately, these PLL chips are expensive, typically they are more expensive then the Microcontroller (MCU) and A/D and D/A chips implementing the system. Therefore, it is reasonable to investigate if it is possible to implement this in system synchronization function utilizing only the built-in peripherals of the MCU, and if it is possible, investigate the achieved performance in detail. In the paper, we present our prototype audio frequency data acquisition system, we introduce the inner algorithms of its synchronization solution utilizing only MCU built-in functions, and investigate the achieved performance. The system uses our open-source flexptp IEEE 1588 implementation (https://github.com/epagris/flexPTP), which is ported to the STM42H743 Cortex-M7 MCU and extended in functionality for this prototype.