hi fat16lib,
it is true that I would have a lot to learn in context switching if the goal for SCoop was to be the best os alternative for the Arduino comunity :).
Now, I feel that the result we get with SCoop is still better than what we get out of the box from other rtos for the following reason :
SCoop is designed for the users, (based on my personal experience on selling software and hardware solution for industry in the 90's).
it is not design for the features or for topmost performances; as an example there is no concept of priorities !
but then this is sometime better and let me do the demonstration on an example that you could reproduce easily.
just setup 3 tasks doing a single 32 bits count++ in a loop containing a yield. with 1 specific counter per task count1,2 and 3. nothing else.
then in the main loop, just put another count4++ and 20 calls to yield.
then use a basic test against the standard millis() to stop and print something after 10seconds. of execution. this test is not going to impact the overall timing as there are 20 yields above it, right.
just print the sum of the 4 counters. (I used only Arduino Uno for this example)
with scoop, the value is 1 086 746 , so in 10 seconds we were able to increment 32 bit counters more than 1 million time.
with chibiOS_AVR out of the box, I got 460 855
with chibiOS configured in cooperative mode with CHCONF = 0, I got 413 824
so you understand where the problem comes from : the yield function in chibiOS is switching almost imediately to next task. As each task contains a very basic sequences which probably represent 1 us, then the total time spent in the overhead scheduling is very high compared to the task themselves.
in SCoop, the default yield is more complex in this regards as it checks the total amount of time spent in the task (400us for AVR by default) before accepting a switch. result is obviously less time in switching compared to the time allocated to the task.
and then we get 2 time more CPU time for the task, as the total counter reach 1 million.
so, as you pointed, I m sure that cooperative mode is a good way forward for majority of arduino community and then we need to provide them with mechanisms which are optimized for their usage, from a user standpoint.
I d love to see feedbacks from users about our libraries so that we can improve their usability, but in the meantime lets continue guiding them with our both respective approach !