If I recall correctly, I must not put code in vApplicationIdleHook() which might block, because there is no lower priority task to execute.

I did not realize until now that means I probably should not use xSemaphoreTake() with a time greater than 0. Can I use 0? Or maybe in the implementation, it is ok to use a higher block time. Docs say the reason IdleTask should not block is because there must always be a task ready to run. What if xSemaphoreTake only blocks while a higher priority is using the same resource?

The idle task is the low power task - if you wish it to be - by using it to place the processor into power save mode.

Using 0 for the block time should be fine, as the task will remain in a ready state.

Using none 0 would be ok provided you can guarantee that there is always at least one task that is able to run - which I think would be difficult to guarantee in most applications.

Regards.

Ok, it seems to work. The reason I could block IdleTask on the specific semaphore is because the highest priority task is the other one that takes it. Since that task does not block while having the semaphore, then it will only block after the semaphore is returned, at wich time IdleTask would be readied.

Or is there a flaw in that logic?

Seems to make sense - should work fine. Give it a go.

Regards.

I just realized that increasing from 0 would not serve any purpose, as IdleTask would never begin executing while the higher priority was still executing.

So with this design I don't even need IdleTask to check the semaphore!