Extended Timestamp Counter Using Rollover Tracking

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Solution Overview

Problem

Existing hardware timers in computing devices, such as ASICs and CPUs, provide timestamps with shorter bit lengths that rollover frequently, preventing the generation of longer time values needed for precise timing applications like IEEE 1588v2 Precision Time Protocol (PTP), which requires 64-bit nanosecond precision timestamps.

Innovation Solution

A mechanism to extend the bit length of timestamps by using a rollover counter in conjunction with the hardware TOD counter, incrementing the rollover counter based on detected rollovers and combining it with the hardware counter value to generate extended timestamps, accessible to both kernel and user space processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If shorter length hardware counters are used, then device complexity is reduced, but the duration of action is limited due to rollover resets

Engineering Contradiction:

Improvehardware counter complexityVSAvoidtimer duration before rollover

Core Design Contradiction:

Device complexityVSDuration of action of moving object

Solution Approach 1:

The extended timestamp is segmented into two parts: the original hardware counter value (lower bits) and the rollover counter value (upper bits). The hardware counter continues to operate independently with its original bit length, while the rollover counter tracks the number of rollovers. This segmentation allows the system to maintain simple hardware while achieving extended time duration through software combination of the two counters.

Inventive Principle:

Principle #1Segmentation

2Measurement precision

If longer timestamp values are required, then precision timing capability is improved, but device complexity increases due to need for extended counters

Engineering Contradiction:

Improvetimestamp precision and rangeVSAvoidcounter extension complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The rollover counter acts as an intermediary that bridges the gap between the limited hardware counter and the desired extended timestamp. Instead of modifying the hardware counter itself, the rollover counter mediates by tracking rollover events and combining its value with the hardware counter value to produce the extended timestamp, thus achieving longer timestamp range without increasing hardware complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If hardware counters are reset at intervals, then device complexity is reduced, but loss of information occurs regarding total elapsed time

Engineering Contradiction:

Improvecounter management complexityVSAvoidtotal elapsed time information

Core Design Contradiction:

Device complexityVSLoss of information

Solution Approach 1:

The rollover counter performs preliminary action by tracking and storing the number of rollover events before they occur. Each time the hardware counter rolls over, the rollover counter is incremented, preserving the information about total elapsed time in advance. This allows the system to reconstruct the full extended timestamp even though the hardware counter itself is reset at intervals.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS12627390B2Providing arbitrarily long timer from shorter underlying hardware counter

Publication Date: 2026.05.12 ARISTA NETWORKS INC

AI summary

Systems and methods for extending an original bit length counter maintained by hardware of a network device to generate an extended length timestamp of a longer bit length are disclosed. The extension of the original bit length counter is based on a rollover counter, where the rollover counter is incremented based on the detection of rollovers of the original bit length counter.