OS Integration

The ARXF-CP has been adapted to AUTOSAR compatible Operating System.

Message Queues

The AUTOSAR OS supports no message queue, but the ARXF-CP uses an event queue per task which operates as a FIFO mechanism. Events are allocated in the static memory pools, allocated per SW-C instance. When one object sends a UML event to another object, only the pointer to the event is sent. Moreover, the message queue is implemented as a head and a tail pointer; it can grow dynamically and is not allocated as such.

Task

For each active class, an OS task is used. All sequential classes run in the so-called swc task. See Concurrency

Task details including stack and priority are specified in an AUTOSAR tool as part of the Basic Software or BSW. OS tasks are configured statically: tasks are not created at runtime when an active class is created.

The properties CG::Class::ActiveMessageQueueSize and CG::Class::ActiveStackSize are not used in ARXF_CP_V8.0.1.

Critical Region Handler

By default, the ARXF-CP uses the AUTOSAR mechanism of an exclusive area for critical region handlers: the RTE will generate a entry- and exit function for each exclusive area defined.

An exclusive area must be specified at the AUTOSAR level per SWC. Code generation for composing RTE function pointers require:

the stereotype CpExclusiveArea on the exclusive area attribute of an SWC
an exclusiveAreaAccess stereotyped dependency between a runnable and this exclusive area. See Profiles.

The enter- and exit functions are generated by the RTE: within the RTE configuration it is defined which interrupts are blocked: this is ALL_INTERRUPT_BLOCKING or OS_INTERRUPT_BLOCKING, but also the BSW scheduler configuration and OS task types are of influence.

The ARXF-CP requires at least three exclusive areas:

one for manipulating the static allocated memory pools
This list is maintained globally per SW-C instance or prototype.
one for manipulating the static allocated timer list
This list is maintained globally per SW-C instance or prototype.
one for manipulating the static allocated event list for the swc task
This list is maintained globally per SW-C instance or prototype.
one for manipulating the static allocated event list for each active class.
This list is maintained globally per SW-C instance or prototype where the class is part of.

When the ARXF-CP is initialized, usually at SW-C initialization time, a call to RXF_SWC_Init() is performed, passing the function pointers to the RTE generated entry- and exit functions as arguments.

It is possible to safeguard critical regions yourselves:

at the AUTOSAR level, an exclusive area must be configured.
The RTE will generate a contract for your SW-C: this will be Rte_<swc>.h
at the Rhapsody level, you will see such exclusive area when you import ArXML with the Software Component Description
the RTE will generate an entry- and exit function for that exclusive area, which act like a critical region handler.

You can also use the properties to specify your own critical region handler. This is done via properties set on the Code Generation tab of the ARXF-CP Configuration.

Timer

The ARXF-CP does not set any timer, but it does need a regular heartbeat. In the Getting Started examples, the runnable <swc>_eventDispatcherSwc is used, which is called by the RTE every 10 msec.

The timer granularity must match the value of RXF_MS_PER_TICK, see List of Defines

The ARXF-CP uses a global counter which is local per SW-C instance. This counter needs to be incremented. The resolution determines the timeouts you can effectively specify in your model: if the runnable is called every 100 msec, specifying tm(10) makes no sense..
See Realtime behavior for further details.

sample code snippet taken from a <swc>_eventDispatcherSwc:

Explanation:

first, a pointer to an ARXF-CP task pointer is retrieved.
For this, the task pointer to that object has been stored during initialization of the SW-C into an inter-runnable, for which the RTE has generated a setter and getter.
we test if this is a NULL pointer (the RTE has not stored yet our task pointer) or our SWC instance has not been initialized yet: <swc>_init() has not been called yet.
the task pointer points to an ARXF-CP SWC structure or actually instance
the timer ticks for this SW-C instance is incremented.
the UML event queue is processed. The function RXF_Active_execute() returns when there are no more events in the queue or a maximum number has been processed.