CS452 - Real-Time Programming - Spring 2010

Lecture 18 - Task Structure

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Anthropomorphic Programming

We all, most programmers included, have effective intuitions about human relations

Tasks are independent entities


Servers and Attendant Tasks

Why do servers need attendant tasks?

1. Proprietor with a Notifier

Proprietor `owns' a service, which usually means a resource.

Kernel is handling hardware in this example

Notifier Code for a UART

Proprietor/Notifier Code for a UART

Notes

  1. Notifier is usually of higher priority than server
  2. When, and how, do interrupts get turned on and/or cleared?
  3. Who coordinates hardware ownership?
  4. We have made the code

2. Using a Courier

Simplest is best

Notifier Code

Courier Code

Proprietor Code

Notes

This gets you through a bottleneck where no more than two events come too fast.

Remember that all the calls provide error returns. You can/should use them for error recovery

Another possible arrangement for initialization

Distributed gating


3. Using a Warehouse

Add a warehouse between the courier and the notifier.

Notifier Code

Warehouse Code

Courier Code

Proprietor Code

Note

This structure clears up problems when the notifier runs too fast for the server.

Two issues:

  1. Handles bottlenecks of all sizes.

    Define `bottleneck'.

  2. Server could be buffered on the other side

    Called a guard.

What this amounts to is

Server should be lean and hungry


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