Determination of frequency of timer ticks

Details Determination of frequency of timer ticks Determination of frequency of timer ticks

1999-10-14

2002-12-31

Maung, Zarni (Department: 2154)

Electrical computers and digital processing systems: support

Clock, pulse, or timing signal generation or analysis

C713S501000, C713S503000, C370S253000

Reexamination Certificate

active

06502201

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to information processing systems and more particularly to a methodology and implementation for determining the frequency of system interrupt timing pulses.
BACKGROUND OF THE INVENTION
Computer systems today rely on internal timing signals which are derived from a system clock signal. Programmable timing circuits, using the system clock signal as a primary reference, provide a series of system timing signals which are, in turn, referred to and used for various functions within the system.
One of the inherent sub-systems in a computer system is the generation of interrupt request (IRQ) signals. The purpose of the IRQ signals is to provide a periodic reference time at which the various sub-systems in the computer can request use of the system processor for example.
Current computer systems generally include a programmable interval timer circuit to provide the interrupt signals. The timer interrupt rate or frequency of the interrupt signal is determined by how a programmable interval timer integrated circuit (IC) is programmed. In the absence of a programmed value, a default rate is applied by the system. For example, in one commercially available interval timer circuit, a default rate of 18.2 interrupts per second is set. However, the interrupt rate on a given system can be changed, for example, by an operating system port I/O or by user written device drivers. Thus, the actual frequency of the IRQ signal may not be readily available.
This presents a problem for system performance analysts for example who need to use a sampling technique in analyzing system performance. Using a sampling technique, for example, sample readings are taken on every timer interrupt pulse in order to evaluate system performance. Typically, the address of the code that is interrupted is taken along with the related process and thread identifications. This information is typically recorded for later analysis. However, since the timer interrupt frequency can be changed, and since an accurate value of the actual timer interrupt frequency is needed in order to control analysis tools sample rates, and there is no current way of reading the frequency programmed into the interval timer circuit, there is a need to be able to determine a real time value of the timer interrupt rate on-demand, in order to understand the data collected.
Thus, there is a need for an improved methodology and implementing system which enables an on-demand determination of the actual real time frequency of system timing signals.
SUMMARY OF THE INVENTION
A method and implementing computer system is provided in which the actual frequency of system timing signals is determinable. In one example, an output from a programmable interrupt timer is selectively sampled and processed in order to determine the actual frequency of the interrupt signal. A user may indicate the number of samples upon which the frequency calculation will be based and the determined actual frequency in real time is saved for reference as needed by system requirements and other applications. In one embodiment, the calculated actual interrupt timer frequency, as well as other related information such as time and date of the latest calculation, is presented on a user display device.


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