Browse Prior Art Database

Oscillation Prevention and Margining in Dynamic Frequency Systems

IP.com Disclosure Number: IPCOM000033788D
Publication Date: 2004-Dec-28
Document File: 3 page(s) / 32K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for eliminating unnecessary frequency transitions while maintaining functionality. The disclosed method may be used in conjunction with temperature sensing, voltage droop sensing, or any other applications where the frequency is dynamically changed with respect to an on-die measurement.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 51% of the total text.

Oscillation Prevention and Margining in Dynamic Frequency Systems

Disclosed is a method for eliminating unnecessary frequency transitions while maintaining functionality. The disclosed method may be used in conjunction with temperature sensing, voltage droop sensing, or any other applications where the frequency is dynamically changed with respect to an on-die measurement.

Background

Frequencies on a microprocessor can be dynamically controlled to respond to changes on the processor die, such as voltage droops or temperature fluctuations. For example, by using a temperature sensor, processor frequency can be increased when the temperature is low and decreased when the temperature is high. Similarly, a voltage droop detector can be used to provide a measurement of the supply voltage on the die, and can dynamically reduce the frequency to allow the processor to operate correctly during a droop. Both of these techniques improve the average performance of the microprocessor by reducing the design margins that must be added to ensure correct operation under worst-case conditions.

When designing a dynamic frequency system, care must be taken to guarantee functionality at all times, while minimizing the number of unnecessary frequency transitions.  These frequency changes may result from a temperature or voltage value which remains near the sensing threshold value of the respective sensor, causing an oscillation on the sensor output.  In this case, changing the processor frequency each time the sensor value crosses the threshold results in unnecessary power consumption, and may result in a performance penalty if the clock is gated each time the frequency is changed.

General Description

The disclosed method eliminates unnecessary frequency transitions while maintaining functionality. Figure 1 shows an overview of the system. The microprocessor die contains one or more sensors, which may include temperature and voltage sensors. These sensors are programmed with one or more specific thresholds, and the output bits of the sensors signify whether the quantity of interest is above or below each threshold. The output is connected to a control unit which determines the correct operation frequency, given the sensor values. This control unit may be implemented as a lookup table of frequency values, which is indexed with the sensor values to allow maximum programmability. Alternately, the control unit can be implemented as fixed logic to accomplish the desired algorithm. Once the control unit has decided the correct frequency value, the frequency control bits are sent to the clocking unit which accomplishes the frequency change.  Many different methods are possible for dynamic frequency change; for example, switching between multiple PLLs, or synthesizing a frequency directly using a DLL structure.

Figure 2a shows an example of the disclosed method dynamically responding to a temperature change using a temperature sensor with a single threshold.  At temper...