richard_damon wrote on Monday, March 27, 2017:
A semaphoretake inside an ISR does NOT block the ISR to wait for the semaphore to be raised, it just returns an error code that the take failed (note, the FromISR routines do NOT take a timeout parameter, but a pointer to a variable to indicate if they woke up a task),
If you need to protect a data structure from an ISR, then you need to use a critical secton. This is what FreeRTOS does internally. These critical sections should be kept very short to avoid excessive interfearance with interrupt activity. If the access needs to be more complicated, so you need to use a semaphore (or better a mutex) to protect the update, then you should rework the ISR to trigger a task or call back hook via the service task to perform the update for the ISR and the ISR do the minimal work to provide that task with the data it needs.