Sporadic scheduling of NuttX does not work for multiple threads

[JanStaschulat]

Created an issue at apache/nuttx#2935

Link to example

NuttX example for sporadic scheduling in testing/ostest

Test setup:

• sporadic thread 1 configuration: 20ms/100ms budget/period
• sporadic thread 2 configuration 10ms/100ms budget/period
• the callback function increments a counter every millisecond.
• wait for 10 seconds
• output the number of ms-counters for every sporadic thread

Observation:

• When I configure the application with one sporadic thread and one FIFO thread (with lower priority and 100% CPU utilization), budget enforcement works well.
• When I configure the application with two sporadic threads and one FIFO thread (with lower priority and 100% CPU utilization) budget enforcement does not work any more. I tested the sporadic scheduling with different budget/period configurations: 10ms/100ms and 1second/10seconds (the internal tick - conversion was correct).
• I saw also somewhere the requirement that the buget shall be at most half of the period, so I configured the budget always smaller then half of the period for all individual threads:
  • thread 1: 20ms/100ms
  • thread 2: 10ms/100ms

Problem description
I came to the conclusion, that budget enforcement of the NuttX sporadic scheduling only works for one sporadic thread.
For real applications, I would like to use multiple threads with sporadic scheduling.