This paper first compares the power consumption of a measured system to validate the accuracy of the FPGA power estimation tool, XPower, included in the Xilinx ISE software suite. Following this, several key parameters that influence the overall power consumption in an FPGA design are sampled. Using the software, the power consumption at each sampling point is estimated, and the point with the lowest power usage is identified. This leads to the selection of optimal design parameters, ultimately achieving an energy-efficient system design. In this experiment, a read/write SRAM system implemented on an FPGA was used as a test case. Under the condition of fixed read/write operations per unit time, two parameters—read/write frequency and read/write time duty ratio—were selected for optimization. The final experimental results confirmed the validity of the proposed method.
FPGAs are widely used across various electronic systems, and optimizing their power consumption has become a crucial practical concern. From the earliest FPGA power models [1] to more advanced power estimation techniques [2], and now to the development of dedicated power estimation tools [3], the accuracy of power prediction in FPGA designs has significantly improved. Based on these estimations, this paper introduces the factors affecting power consumption as variables in a power function. By sampling these parameters and estimating the corresponding power values, the minimum of the power function is determined, leading to the identification of optimal design settings. A read/write SRAM system was designed to demonstrate the effectiveness of this approach. By adjusting the read/write frequency and duty cycle, the system’s power consumption was optimized. The method was validated by comparing the estimated power values with actual measurements.
**1 FPGA Power Estimation Tool**
**1.1 Introduction to XPower**
Xilinx's ISE Design Suite includes the XPower Analyzer, a power simulation tool that estimates the power consumption of programmable logic devices [3]. The power consumption is categorized into two main components: static and dynamic. Static power arises from leakage currents in transistors and the bias current of the FPGA, and it depends on process technology, transistor characteristics, and other intrinsic properties of the device. Dynamic power, on the other hand, is associated with the switching activity of the FPGA's internal logic and I/Os during operation.
Dynamic power can be calculated using the formula $ P = C \times V^2 \times f \times D $, where $ C $ is the capacitance, $ V $ is the supply voltage, $ f $ is the clock frequency, and $ D $ is the number of transitions per second. XPower builds a capacitance model for each switching component and uses data from input files such as NCD (Native Circuit Description), PCF (Physical Constraint File), XML (User Settings), and VCD (Value Change Dump) to estimate both static and dynamic power consumption. These files provide critical information about the design layout, constraints, and simulation behavior, which helps improve the accuracy of the power estimation.
The main output of XPower is the PWR file, which contains detailed power consumption reports. It separates the total power into static and dynamic components. While static power remains relatively constant for a given chip, dynamic power varies based on the logic used, clock frequency, and signal activity. Both types of power are also affected by external factors such as voltage and temperature. To ensure accurate results, XPower settings must be carefully configured, especially the VCD file, which captures signal transitions during simulation. Accurate simulation data is essential for reliable power estimation.
The FPGA design flow, shown in Figure 1, highlights the importance of power estimation in the design process. When power efficiency is critical, designers often need to modify the design to reduce power consumption.
**1.2 XPower Reliability Verification**
To measure the actual power consumption of an FPGA, a simple system was built using an adjustable DC power supply. Due to the low power levels involved, it was necessary to account for voltage drop along the power lines. The voltage was measured as close to the FPGA's power pin as possible, and the supply voltage was adjusted to match the design specifications (VCCO = 3.3 V, VCCINT = 1.2 V, VCCAUX = 2.5 V).
After programming the FPGA with the configuration file, the actual power consumption was measured by monitoring the current and voltage. The corresponding XPower input files were used, and the VCD simulation was aligned with real-world excitation conditions. Temperature and frequency settings were also matched to the measured environment. This allowed for a comparison between simulated and actual power consumption under identical operating conditions.
In this experiment, an Xilinx Spartan 3e xc3s100eH FPGA was used at 25°C with a clock frequency of 18.432 MHz. Various configuration files were tested by changing the number of clocks, logic resources, I/Os, and signals. After measuring and estimating the power consumption for each configuration, the results showed a strong correlation between the measured and estimated values, as illustrated in Figure 2. This confirms the reliability of the XPower tool for power estimation in FPGA designs.
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