REAL-TIME OPERATING SYSTEMS AND STANDARDS - Hard Real-Time Computing Systems: Predictable Scheduling Algorithms and Applications - page 445

hard task soft task

QoS Mapper Module 1

soft
model

Internal data
structures

Specific

Generic
Model Mapper

algorithm

hard

model

QoS Mapper Module 2

Internal data
structures

Specific

algorithm

Figure 12.3 The interaction between the Model Mapper and the QOS Mapper.

the scheduling queues of the base scheduling algorithm. Again, the modularity of the
architecture hides this mechanism with the task models: an aperiodic server must use
a task model to insert his tasks into the Host Module. In this way, the Guest Module
does not have to rely on the implementation of the Host Module.

The Model Mapper distributes the tasks to the registered modules according to the task
models the set of modules can handle. For this reason, the task descriptor includes an
additional field ( task level ), which points to the module that is handling the task.

When the Generic Kernel has to perform a scheduling decision, it asks the modules
for the task to schedule, according to fixed priorities: First, it invokes a scheduling
decision to the highest priority module, then (if the module does not manage any task
ready to run) it asks the next high priority module, and so on. In this way, each module
manages its private ready task list, and the Generic Kernel schedules the first task of
the highest priority non empty module's queue.

The interface functions provided by a scheduling module can be grouped in three
classes: Level Calls, Task Calls and Guest Calls.