Clock, system

The system clock is used for timekeeping functions as well as to schedule context switches in the kernel.

PIT-based system clock

SVR5 and SCO OpenServer Release 5.0.5 and earlier use a system clock based on the enhanced 8254 PIT (Programmed Interrupt Timer) that is included on 386/486 machines.

High-precision system clock (SCO OpenServer 5 only)

Beginning with SCO OpenServer Release 5.0.6, SCO OpenServer 5 uses a new high-precision system clock, documented on the clock(HW) manual page. The new timekeeping and alarm subsystem offers microsecond-precision, replacing the old 10-millisecond-precision clock.

The high-precision system clock has the largest impact on heavily clock dependent applications such as animation, audio/video recording and playback, and motor controls. Most application programs and drivers do not need to be modified or recompiled to take advantage of the new functionality but will perform better when run on a system that uses the high-precision system clock.

Drivers that are heavily clock dependent can avail themselves of the following capabilities in ODDI version 6 and later drivers:

• The nano_timeout(D3oddi) function accesses a nanosecond-precision alarm timer within the kernel.

• The suspend(D3oddi) kernel function provides alarm timers with full microsecond-precision.