Realtime

Digital UNIX Version 4.0 supports a realtime user and programming environment, developed by Digital and shipped as an optional realtime subset. The Digital UNIX Version 4.0 realtime programming environment conforms to the POSIX 1003.1b-1993 standard for realtime which allows you to develop and run portable realtime applications in a POSIX environment. The realtime interfaces are collected in the static and shared libraries /usr/ccs/lib/librt.a and /usr/shlib/librt.so, respectively.

If you enable kernel preemption, a higher-priority process can preempt a lower-priority process regardless of whether it is running in kernel mode or user mode. With this fully preemptive kernel, the Process Preemption Latency (the amount of time it takes to preempt a lower-priority process) is minimized.

In addition to a preemptive kernel, the Digital UNIX Version 4.0 realtime programming environment supports the following POSIX 1003.1b features:

• Realtime clocks and timers

• Realtime Queued Signals

• Fixed priority scheduling policies

• Realtime scheduler priority levels

• Counting Semaphores

• Shared memory

• Process memory locking

• Asynchronous I/O

• Synchronized I/O

• Message-passing interfaces

• Thread-safe implementation of realtime libraries

For more information on the realtime programming environment, see the Guide to Realtime Programming. For information on configuring the realtime kernel, see the System Administration guide.