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 Kernel Products
smx++ ™
smx++ is a C++ interface to the smx multitasking kernel. It is a class library that implements most kernel services. It is recommended for C++ projects.
Most classes correspond directly to smx objects, and most class methods correspond directly to smx functions. Class Hierarchy
This interface opens up the world of context sensitivity, function overloading, virtual functions, modularity, and inheritance to the embedded system programmer. It is more than a C++ wrapper — it is an environment.
For example, the user may create a unique object derived from the smx_Task class. It would include all smx++ objects which are associated with the task. The derived task is completely modular and includes all data and methods which are required by the task. For example, a serial communications task object might include an interrupt service routine, an smx_LSR object, an smx_Pipe object, and an smx_MsgXchg object.
For existing smx C applications, smx++ allows an easy transition to C++. Since smx underlies smx++, direct calls to smx C APIs are still possible, permitting a mixture of C and C++ usage. This evolutionary approach allows incrementally migrating to C++. New functionality can be added using the smx++ API, and old functionality can be gradually converted, as convenient.
More Than a Wrapper
C++ experts might be tempted to develop their own C++ API for smx. We recommend smx++ for C++ programmers from expert to novice because it is more than just a wrapper:
- this support: C++ compilers do not assume a multitasking environment. When a task is created it is not in its own environment. Hence its this pointer must be captured and saved in its TCB. When the task runs, its this pointer is restored. (Where, depends upon C++ compiler internals.)
- When used as intended, C++ code does frequent object creations and deletions via the new() and delete() operators. C++ compilers implement these via the heap functions, malloc() and free(). This can lead to severe heap fragmentation and slow, indeterminate allocations. These are unacceptable in embedded systems which have limited RAM and require fast, deterministic operation. To overcome this problem, smx++ permits overloading new() and delete() with raw block pools. Overloading may be done on a class by class basis to permit exact-size blocks or on a class group basis to reduce pools. Since raw blocks also do not have associated control blocks, very efficient memory utilization can be achieved.
- TimerLSR object: Integrates the smx timer and LSR into a single object.
- Task object: Has integrated main function and hooked exit/entry routines that make tasks easier to use than with the C API for smx. Also adds numerous methods to perform operations that would otherwise require directly accessing TCB fields.
- Message object: Goes far beyond the capabilities of the MCB. Tracks size and other details automatically. Also adds extra error checking abilities. This is a container rather than a wrapper and has the benefits of a container.
- Copy constructors allow the user to easily make copies of complex objects such as multi-level queues.
- Global C++ object support: Initialization, creation, and destruction.
Class Hierarchy Chart (PDF)
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