PIC18F97J60+MRF24WB APPDEMO main loop

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(cooperatibe multitasking)

Once your program has been initialized, you should enter an infinite loop which will handle your application tasks. Within this loop, there are two functions that you must call regularly: StackTask and StackApplications. 

The StackTask function will perform any timed operations that the stack requires, and will handle transmission and reception of data packets. This function will also route any packets that have been received to the appropriate application protocol-level function to handle it. 

The StackApplications function will call loaded application modules. For example, if an application is using an HTTP2 server, StackApplications will automatically call the HTTPServer function to process any HTTP2 tasks that are queued. 

Most sub-tasks within StackTask and StackApplications are implemented as state-machine controlled cooperative multitasking functions. Since these sub-tasks consists of multiple steps (which may occur at varying times) this call-back system ensures that no single task will monopolize control of the processor. 

Within this main loop, you may also want to poll for any I/O changes in your application and call any application specific tasks that you've implemented. To avoid causing buffer overflows in your hardware or protocol timing violations you should try to implement your own application tasks in callback functions with timing-based triggers. A method to do this is described in the next topic. 

You must make one call to StackTask for each call of StackApplications but you aren't required to call these functions with any specific frequency. Calling StackTask too infrequently could limit your throughput, though, as each call of StackTask can retrieve one packet (at most) from the packet buffer. Similarly, application tasks that are time-dependant (like an ICMP ping response) may produce undesirable results if StackApplications is not called frequently enough. 

The amount of time that the main loop takes to complete one iteration depends on several factors. If data is ready to be transmitted, or if a packet of received data was received, the StackTask function will take more time than it would otherwise. Each additional protocol included in your application will cause the main loop to take additional time as well, with the amount of time for each varying from the length of the shortest state machine state in the task to the longest. 

Once your application is complete, you can set up a test case to determine the min/average/approximate maximum time that your loop will take to run. You can set your code up to use an internal timer to measure the duration of each iteration of the main loop, or you can set the code up to trigger an output pin each time the main loop completes, and use an oscilloscope to capture the network execution time. You can then provide application inputs or additional network traffic with a PC program (or other PICs) to simulate real-world operating conditions.