Chapter 180. Overview

Introduction

The Common Clock package (CYGPKG_CLOCK_COMMON) provides a centralized management interface for system time, also known as calendar time, which corresponds to the real time of day. System time is distinct from other clock-related concepts such as the kernel "real time clock" which drives the kernel scheduler, or hardware timers.

The purpose of this package is primarily to keep system time management and related functionality focused in a central location to ensure a consistent and coherent approach to time management across all eCos packages, and to avoid duplication. It is used by the C library and by the POSIX compatibility layer for underlying time support, and also provides interfaces to manipulate time which may be used by services such as NTP, as well as to the user. It encapsulates the underlying eCos wallclock driver layer.

At the present time, it only operates when using the eCos kernel package, as it uses a dedicated thread to perform time management functions.

It has been verified safe for use past year 2038 - the so-called Year 2038 problem refers to the overflow of signed 32-bit representations of time in seconds since 1970-01-01 00:00:00 UTC.

2017-02-09
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