Echelon FTXL - Manual (Page 88)

76 Developing an FTXL Application
o Future versions or fixes to the FTXL product might affect these
API files
Callbacks and Events
The FTXL LonTalk API uses two types of notifications for occurrences within the
system: callbacks and events.
The FTXL LonTalk API uses a
callback when the API needs a return value from
the application immediately. A callback can occur in one of the FTXL LonTalk
protocol stack contexts (tasks or threads).
When you implement a callback handler function to process a callback, you must
ensure that the function completes its work as quickly as possible. Generally, a
callback handler function must not call FTXL LonTalk API functions or perform
time-intensive operations.
The FTXL LonTalk API uses an
event to deliver a one-way notification to the
application. The protocol stack does not wait for the processing of the event to
complete before continuing.
The FTXL LonTalk protocol stack holds events in an internal queue for
processing. Thus, the application program must periodically call the
LonEventPump() function to process the event queue. This function also calls the
related event handler functions.
Because event processing in the event handler functions is not tied to the context
of the protocol stack, an event handler function can call FTXL LonTalk API
functions or perform time-intensive operations. An event handler function runs
within the same context (task or thread) as its caller (the LonEventPump()
function).
See Appendix D,
FTXL LonTalk API , on page 147, for a list of the callback
handler functions and event handler functions.
Integrating the Application with an Operating System
The FTXL LonTalk protocol stack requires an FTXL application to use an
operating system. The FTXL Developer’s Kit includes example applications that
use the Micrium μC/OS-II operating system, but you can use any embedded
operating system that meets your application’s requirements. Although the
μC/OS-II operating system is a real-time operating system, the FTXL LonTalk
protocol stack does not require the operating system to be a real-time operating
system.
To allow the FTXL LonTalk protocol stack to use any operating system, the FTXL
LonTalk protocol stack library is linked with the FTXL Operating System
Abstraction Layer (OSAL) files, FtxlOsal.h and FtxlOsal.c. The FTXL OSAL files
provide macros and C functions for general operating system functions, such as
creating semaphores and waiting for events. The FTXL OSAL functions also
include error handling and basic debug tracing for the operating system
functions.
Your FTXL application can call the FTXL OSAL functions when it needs to call
operating system functions, or it can call the operating system functions directly.
By calling FTXL OSAL functions, your FTXL application can be more easily
ported to another operating system, if needed.