Cost-effective Energy Monitoring of a Zynq-based Real-time System including dual Gigabit Ethernet

Abstract

The ongoing integration of fine-grained power management features already established in CPU-driven Systems-on-Chip (SoCs) enables both traditional Field Programmable Gate Arrays (FPGAs) and, more recently, hybrid Programmable SoCs (pSoCs) to reach more energy-sensitive application domains (such as, e.g., automotive and robotics). By combining a fixed-function multi-core SoC with flexible, configurable FPGA fabric, the latter can be used to realize heterogeneous Real-time Systems (RTSs) commonly implementing complex application-specific architectures with high computation and communication (I/O) densities. Their dynamic changes in workload, currently active power saving features and thus power consumption require precise voltage and current sensing on all relevant supply rails to enable dependable evaluation of the various power management techniques. In this paper, we propose a low-cost 18-channel 16-bit-resolution measurement (sub-)system capable of 200 kSPS (kilo-samples per second) for instrumentation of current pSoC development boards. To this end, we join simultaneously sampling analog-to-digital converters (ADCs) and analog voltage/current sensing circuitry with a Cortex M7 microcontroller using an SD card for storage. In addition, we propose to include crucial I/O components such as Ethernet PHYs into the power monitoring to gain a holistic view on the RTS's temporal behavior covering not only computation on FPGA and CPUs, but also communication in terms of, e.g., reception of sensor values and transmission of actuation signals. We present an FMC-sized implementation of our measurement system combined with two Gigabit Ethernet PHYs and one HDMI input. Paired with Xilinx' ZC702 development board, we are able to synchronously acquire power traces of a Zynq pSoC and the two PHYs precise enough to identify individual Ethernet frames.