Serial and systick events handling about xmc-for-arduino HOT 8 CLOSED

/* Includes Co-operative Scheduler for XMC-for-Arduino

   Using COMPILE time scheduling table 

Version V1.00
Author: Paul Carpenter, PC Services, <[email protected]>
Date    March 2018

Co-operative scheduler library that has some support functions and main 
schedule function meant to be run as the Systick scheduler event handler, the 
support functions should be used to get status on, start, stop, or configure tasks.

The schedule code is designed for MINIMAL overhead and SPEED.

The time interval of calling the schedule loop is determined by Systick timer 
interval currently 1 ms, and calls a selection of tasks determined by two
parameters for each task

    callback    function address
    parameter   INTEGER to pass to function
    
From this we get TWO types of function calls when a task event happens

1/ callback and parameter are set gives a function call of

    int callback( int ID, int16_t param )
            function to use as this task that accepts TWO integer parameters
            and MUST return an integer

   (even if parameter not set it is initialised to task_id AT compile TIME)
    
2/ Special case if ANY task has its callback set to NULL a special variable
   in wiring_time is set to TRUE. This enables the delay() function to work
   for ms delays. As a side effect it stops runaway tasks for callback set to 
   NULL. 
                            
Callback functions in list
--------------------------
    For different processors speeds it is suggested to keep the number of 
    total tasks (callback functions) to following limits -
    
    Speed               Max Tasks
    < 50 MHz            8
    > 50 MHz < 100 MHz  12
    > 100 MHz           16

Callback function structure
---------------------------
    Task is actually calling a function that should be defined as 
    function that returns int and takes TWO integer parameter

    e.g.    int func( int TaskId, (int16_t Parameter )
    First parameter is TaskId,
    Second parameter is user defined parameter (int16_t)

    If interval of a task has to change call setInterval during task execution
    NOT to STOP task use return code

Callback functions Contents
---------------------------
    Callback functions are effectively interrupt routines so care should be taken 
    about which variables and flags set in these functions are volatiles.
    
    Functions MUST be VERY SMALL as many tasks have to run in less than 1 ms as 
    well as the main code.
    
    Do NOT use blocking or slow callbacks that use AT LEAST the following Ardunio
    functions
        delay           (this would become recursive)
        .print, .write, println on Serial or Liquid Crystal
        analogread
        PulseIn
        Liquid Crystal  ANY function
        I2C or SPI      ANY function
        SD/MMC          ANY function

    All of these and maybe others are SLOW, block waiting for I/O or time
    delays often MUCH longer than 1 ms

Callback Function Return value
------------------------------
    The returned value is the NEW status for that task which tells scheduler
    what to do next time. Values are

      < 0 User error status (stops task execution)
        0  Task stopped (if needed to be run will have to be started by Start)
      > 0 Next status this can be used by call back function for state machines
          Task runs again at the interval set

Scheduling Functions
--------------------
setInterval Set a task's NEW interval and schedule new time from now if not
            already running
getInterval Get a task's interval
setParam    Set a task's callback function parameter (signed int16_t)
getParam    Get a task's callback function parameter (signed int16_t)
getTime     Get a task's next time to execute
getStatus   Get a particular task status word
StartTask   Start a task (if not already running)
FindID      get ID of first task from task address
*/