This paper first evaluates the accuracy of the XPower tool, an FPGA power estimation software included in Xilinx ISE, by comparing its power consumption predictions with actual measurements from a real system. Following this, several key design parameters that influence power consumption in an FPGA are analyzed. By sampling various operational points and estimating power using the software, the configuration with the lowest power usage is identified, allowing for the selection of optimal design parameters to achieve energy-efficient system performance. In this specific experiment, an FPGA-based SRAM read/write system was used, and under fixed read/write operations per unit time, two critical parameters—read/write frequency and duty cycle—were optimized to reduce power consumption. The results confirm the effectiveness of the proposed method.
FPGAs are widely used across various applications, and optimizing their power consumption has become a crucial challenge. From early power models [1] to more advanced estimation techniques [2], and now to integrated tools like XPower [3], the ability to accurately estimate power has improved significantly. Based on these estimations, this paper introduces a power function where key factors affecting power consumption are treated as variables. By sampling different parameter combinations and estimating the resulting power, the minimum value of the function is determined, leading to the identification of optimal design settings. A practical implementation of this approach is demonstrated through an SRAM read/write system, where read/write frequency and duty cycle were selected as the optimization targets. The method's validity is confirmed by comparing estimated values with measured data.
**1 FPGA Power Estimation Tool**
**1.1 Introduction to XPower**
Xilinx’s ISE Design Suite includes the XPower Analyzer, a tool designed to simulate and estimate power consumption in programmable logic devices [3]. Power consumption in FPGAs is typically divided into two main components: static and dynamic. Static power arises from leakage currents in transistors and the bias current of the FPGA, which depend on process technology, transistor characteristics, and dielectric materials. These factors are inherent to the device and remain constant regardless of circuit activity. Dynamic power, on the other hand, occurs during switching events in the device core or I/Os. It is calculated using the formula: $ P = C \times V^2 \times f \times D $, where $ C $ is capacitance, $ V $ is voltage, $ f $ is clock frequency, and $ D $ is the flip rate per node per second.
XPower constructs a capacitance model for each switching component, using input files such as NCD (Native Circuit Description), PCF (Physical Constraint File), XML (User Settings), and VCD (Value Change Dump) to estimate power consumption. The NCD file provides layout information, the PCF defines clock and voltage settings, the XML stores user preferences, and the VCD captures signal changes during simulation, making the estimation more accurate. The main output of XPower is the PWR file, which reports both static and dynamic power. While static power remains relatively stable, dynamic power varies based on the number of I/Os, DCMs, DSP modules, and switching rates. Both types of power are also influenced by operating voltage and ambient temperature. Accurate parameter settings, especially the VCD file, are essential for reliable estimates.
The FPGA design flow, shown in Figure 1, highlights the importance of XPower in power analysis. When power efficiency is critical, design modifications may be necessary to reduce consumption.
**1.2 XPower Reliability Verification**
To validate XPower’s accuracy, a simple FPGA system was built, powered by an adjustable DC supply. Voltage drop along the power line was carefully considered, and measurements were taken close to the FPGA’s power pins. The target voltages were set at 3.3 V (VCCO), 1.2 V (VCCINT), and 2.5 V (VCCAUX). After configuring the FPGA, actual power consumption was measured by monitoring current and voltage. The same configuration file was used in XPower, and the VCD file was aligned with real-world signals. Temperature and frequency settings were matched to ensure consistency between simulation and measurement.
The test involved a Xilinx Spartan 3e xc3s100eH at 25°C and 18.432 MHz. Different configurations were tested by varying clock count, logic usage, I/Os, and signal numbers. Measured and estimated power values were compared, showing a strong correlation. As illustrated in Figure 2, the measured curve closely matches the simulated one, confirming the reliability of XPower.
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