Commits on Jun 7, 2024

1. Tickless scheduler …

   This commit incorporates several changes:
   
   Timers are now not set for a regular tick, they are set when a thread
   may be preempted.  Specifically, the timer is set to the next timeout
   that will trigger a scheduling operation.  This avoids timers
   triggering a switch to the scheduler to do nothing (resume the currently
   running thread).
   
   This means that if a thread sleeps for ten ticks while another runs, we
   will get one timer interrupt ten ticks in the future, rather than ten
   interrupts one tick apart.
   
   This means that ticks are now calculated retroactively based on elapsed
   time, rather than counted on each context switch.
   
   This, in turn, necessitates some small API changes.  We previously
   conflated two things:
   
    - Sleep for N * (tick duration)
    - Yield and allow lower-priority threads to run for, at most, N * (tick
      duration)
   
   These are now deconflated by adding a second parameter to thread_sleep.
   Most sleeps are of the second form and so this is the default.
   
   This reduces the time taken to run the test suite on Sonata by around
   30% and in the Ibex SAFE simulator by 13%.

   

   davidchisnall committed Jun 7, 2024
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