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发信人: zpw (zhao), 信区: Programming
标  题: FAQ for VXD(之五)
发信站: 紫丁香 (Tue Jul 28 14:13:17 1998), 转信

Can I use Windows as a real-time operating system?
     Can you say semi-real-time?� Microsoft Windows is not designed as a real
     time operating system. In other words, there are no guarantees of real
     time performance. Let me repeat that. There are NO GUARANTEES for real
     time latency under any version of Microsoft Windows. If your application
     requires absolutely guaranteed real-time response, otherwise a plane will
     crash, a nuclear reactor will melt down, or a patient may die, then DO NOT
     use Windows as a platform. On the other hand, if you can design you
     application (hardware/software) to accommodate some delays, you will find
     that in most cases, Windows can provide excellent average latencies.

     For example, experiments run on a 486/66 system with no other programs
     running suggest that a VxD can handle over 10,000 interrupts per second
     without losing any of them. However, as soon as other software is loaded,
     interrupts begin to be dropped.

     Windows is an open system� in the sense that applications and drivers can
     disable interrupts at will. If one device driver disables interrupts for a
     long period of time, no interrupt servicing will be performed. While new
     drivers tend to keep interrupts disabled for very short periods, older
     drivers and applications sometimes poll hardware devices and keep
     interrupts disabled for unpredictable amounts of time.

     Of course, you can write a driver that disables interrupts and polls YOUR
     hardware. The mouse and keyboard will not respond, and other device driver
     developers will grumble and curse if your driver happens to running on a
     system where THEY want to do real-time-like operations. However, this may
     be an acceptable alternative for in-house projects, or on well controlled
     systems.

     The only real answer is to test your driver with a wide variety of software
     and hardware installed and gather empirical evidence. If you have the
     luxury to control the design of the hardware, build in buffering to
     accommodate worst-case latency situations.

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※ 来源:．紫丁香 bbs.hit.edu.cn．[FROM: yaoyu.hit.edu.cn]

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