Toggle rate – Altera PowerPlay Early Power Estimator User Manual
Page 53
Altera Corporation
3–39
May 2008
PowerPlay Early Power Estimator For Arria GX FPGAs
Using the PowerPlay Early Power Estimator
Factors Affecting
PowerPlay Early
Power Estimator
Spreadsheet
Accuracy
There are many factors that greatly affect the estimated values displayed
in the PowerPlay Early Power Estimator. In particular, it is imperative to
determine whether or not the input parameters entered are accurate to
ensure that the system is modeled correctly in the PowerPlay Early Power
Estimator spreadsheet. In particular, information entered concerning
toggle rates, airflow, temperature and heat sinks are extremely
important.
Toggle Rate
The toggle rates specified in the PowerPlay Early Power Estimator
spreadsheet can have a very large impact on the dynamic power
consumption displayed. In order to obtain an accurate estimate it is
imperative to input toggle rates that are realistic. Determining realistic
toggle rates is a non-trivial problem that requires the designer to know
what kind of input the FPGA is receiving and how often it toggles.
If the design is not yet complete, it is very difficult to get an accurate
estimate. The best way to approach the problem is to isolate the separate
modules in the design by functionality and estimate resource usage along
with toggle rates of the resources. The easiest way to accomplish this is to
leverage previous designs to estimate toggle rates for modules with
similar functionality.
As an example, let us assume that there is a simple design that has an
input data bus that has been encoded for data transmission and has a
roughly 50% toggle rate. It then goes through a decoder and is stored in
RAM. The data is then filtered before being modulated with another
input data bus and the result is encoded for transmission. A simple block
diagram is shown in
Figure 3–29. Decoder & Encoder Block Diagram
In this case the designer would have to estimate the following:
■
Data toggle rate
■
Mod input toggle rate
■
Resource estimate for Decoder module
■
Resource estimate for RAM
■
Resource estimate for Filter
■
Resource estimate for Modulator
Decoder
RAM
Filter
Modulator
Encoder
Mod Input
Data