REACT (tm) in IRIX (tm) Version 5

Real-Time Extensions In IRIX (tm) Version 5 For CHALLENGE (tm) And Onyx (tm)

IRIX is Silicon Graphics' implementation of UNIX (r) System V, Release 4 (SVR4). The REACT extensions to SVR4 enable users to configure their system to deliver deterministic responses to external events. The REACT extensions are an integral part of IRIX, and are included in every copy.

When running on a multiprocessor CHALLENGE server or Onyx graphics system, IRIX with REACT provides a powerful solution for real-time simulation, data acquisition and telemetry applications. Simulation applications include flight and vehicle simulators, power plant simulators, and hardwarein-the-loop test simulators.

Features

Fast, Deterministic System Response

On a properly configured multiprocessor system, total interrupt response time is less than 200 us, from occurrence of the interrupt to initiation of the user's application process.

Full Control Over Real-Time Processors

By allocating one processor of a multiprocessor system to handle UNIX system functions, the remaining processors can be exempt from all system overhead, including scheduler activity. Real-time processes have full control over these processors. The user can precisely specify assignment of processes to processors, process priority, and routing of interrupts to processors.

Standard UNIX

IRIX conforms to numerous application programming interface standards, including POSIX 1003.1a, FIPS 151-1, SVID3 and XPG3. In addition, it includes important functionality specified in POSIX 1003.4, and in upcoming releases will become fully compliant with this standard.

Periodic Scheduling

Internal timers can be used to initiate frames in simulation applications. Scheduling of processes on any subset of processors can be synchronized to a frame. Multiple independent frame rates can be maintained concurrently.

Sub-Microsecond Accuracy Timers

On CHALLENGE and Onyx systems, each processor includes an interval timer with submicrosecond accuracy. Each timer can be set to interrupt its processor at intervals ranging from 400 ((***))) to 200 hours. Interrupts can be either one shot or repetitive. Each processor also has access to a free-running timer that can be used to measure elapsed time with sub-microsecond accuracy.

Queued Signals

Queued signals, as outlined in POSIX 1003.4, guarantee that the number of signals received by a process is identical to the number sent to that process. IRIX supports 64 queued signal levels, including 32 reserved for real time. The 32 realtime signals each have a separate prio rity level. Queued real-time signals are delivered in order of their priority.

High-Level Language Support

Support for Fortran, Ada, C and C++ enable efficient development of highquality, real-time application software.

CHALLENGE And Onyx Hardware Features

Scalable, Shared Memory, Symmetric Multiprocessing

A cache-coherent, shared-memory architecture simplifies programming and communication among processors. Scalable processor, memory, and l/O configurations can be matched to an application, then later expanded in the field, if needed.

High-Performance VME Buses

Base configurations include a VME64 I/O bus capable of sustaining transfer rates of over 50 MB/Sec. VME capability can be expanded up to 5 VME64 buses, with 25 slots in CHALLENGE and 23 slots in Onyx. All slots are fully compatible with 32-bit VME boards.

VME DMA Controller

Each VME bus controller includes a general-purpose, block-mode DMA controller. This enables applications to move data using high-speed DMA transfers between system memory and VME boards, which support only slave-mode operations. The DMA control registers are mapped into the user's address space, eliminating the overhead of a system call when initiating a DMA transfer.

Standard Computing Platform

Real-time applications can use the same Silicon Graphics models that are currently in use in thousands of technical computing installations. The performance, cost effectiveness and rapid pace of technological improvement of these products are unmatched by proprietary real-time computer systems.

Fast, Deterministic UNIX

IRIX with REACT includes the following extensions to UNIX, which result in a fully deterministic multiprocessor system that is suitable for de manding realtime applications.

Precise Priority Control

Users can assign a process to one of three priority bands: above, equal to, or below normal UNIX processes. Within each band, processes can be as signed to one of at least nine priority levels.

Non-Degrading Priority

Users can prevent the UNIX scheduler's aging mechanism from decreasing the priority of a process as its run time accumulates. This freezes the proc ess priority at the assigned level.

Memory Page Locking

Users can lock a process into memory, ensuring that it will never incur a page fault.

Process-To-Processor Locking

On a multiprocessor system, processes can be locked onto or off of a processor, and interrupts can be directed to specific processors.

Processor Isolation

On a multiprocessor system, processors can be isolated from interprocessor interrupts associated with cache and memory management. Isolated processors can communicate with any other processors via shared memory.

Disabling The UNIX Scheduler

If total user control over a subset of processors is desired, the user can exempt those processors from being controlled by the UNIX scheduler. This ensures that the current user process will never be preempted (except to handle interrupts), and eliminates the overhead of cycles spent running the scheduler. Scheduler services remain available to run the next-highest priority process if the currently running process yields.

Commitment To The Real-Time Market

Silicon Graphics was the first manufacturer of general pu rpose UNIX workstations and servers to offer a solution to demanding real-time applications.

Silicon Graphics is committed to expanding its leadership role in offering standards-based sol utions for applications such as real-time simulation, data acquisition and telemetry. Key elements of this commitment include continuing enhancements of IRlX's real- time features and tools, conformance to standards such as POSIX 1003.4, and strong partnerships with third-party VME suppliers.