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  • Author Author: loucovey
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Microcontrollers with real-time advantages

loucovey


BY JIM HARRISON

Electronic Products West Coast Editor

You can make the most powerful CPU possible, but if you can’t connect to the outside world efficiently, it’s all for naught. This is especially true for real-time systems that can’t afford to wait around to get bytes out.

Some processor folks have implemented what’s often called event management This takes the communication load off of the CPU, normally driven by an interrupt. That interrupt usually takes on the order of 20 to 50 clock cycles; by the time the processor saves the context for a limited number of registers, accesses a peripheral, saves the data, restores the context, and perhaps deals with a pipeline flush.

Read more on MCUs with event management at ElectronicProducts.com

  • Since I began working with computers in the early 1970's, I/O has always slowed down realtime computing issues.  When I started to model systems, I would usually find that the processors were only loaded to about 50% for real applications.  The I/O and context switching ate up the rest of the time.

    You also have to be careful with DMA, those CPU cyles are not "free", they cost the processor time.  I made a good living modelling computer architectures and networks to show people that they either had too little or too much processing capacity, depending upon their application.

    Even storing the data in memory and using buffers only buys you so much.  In highly reactive systems even those implementation may not be enough.

    So make sure that you carefully analyze your system threads and the components selected to interface to the real world.  You will usually find a surprise issue that impairs your performance under certain opperating scenarios.

     

    Thanks

    DAB