RAM 6.0 BUX II Series Betriebsanweisung PDF herunterladen (Seite 19)

7. Devices

or an In-Circuit Emulator. Emulator object file formats and operations are as varied

as the vendors that sell them. Contact Wind River for information on appropriate

combinations.

The initial goal should be to get serial line activity. Start small. Build a simple

polled serial driver and build up from there. Take advantage of any LEDs that can

be blinked as checkpoints in the code are passed. Use an oscilloscope to see that

interrupts are occurring and being acknowledged correctly.

See the VxWorks BSP Developer’s Guide for more information on strategies for

dealing with the initial startup of a new BSP.

7. Devices

Devices should support both read and write access; it is both expensive and error

prone for software to keep copies of registers or other data written to a device.

Devices that have mandatory access timing requirements should not expect

software to delay between accesses. This is both error prone and non-portable.

Instead, they should automatically suspend the next access.

The rest of this section discusses more specific areas of concern for devices that

may be used in your real-time system.

Interrupts

Interrupts are a major consideration in any real-time system. The issue of interrupt

latency can have major influence on system design. The interrupt handler

mechanism in VxWorks is designed to provide minimum interference between the

interrupt event and the execution of the interrupt handler routine. A minimum

response time is published in the benchmarks.

All of this effort could go to waste if the hardware interrupt circuits are designed

in a way that makes interrupt handling cumbersome or inefficient. This is one

reason why certain hardware is not suited to real-time systems design.

Another important fact is that the device drivers are often intentionally written to

disable interrupts for a brief period of time. This is done to guard data variables

that are shared (between task level code and the interrupt handler) from

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RAM 6.0 BUX II Series Betriebsanweisung Seite 19