42ef2887f4
fix(esp_driver_gptimer): do gptimer retention by timer unit rather than timer group (v5.3) See merge request espressif/esp-idf!35358
GPTimer Driver Design
State Transition
State transition is achieved by using the primitives provided by
<stdatomic.h>.
Other functions won't change the driver state. The functions above labeled with * are allowed to be used in the interrupt context.
Concurrency
There might be race conditions when the user calls the APIs from a thread and interrupt at the same time. e.g. a Task is just running the gptimer_start, and suddenly an interrupt occurs, where the user calls gptimer_stop for the same timer handle. Which is possible to make a "stopped" timer continue to run if the interrupt is returned before the Task.
By introducing a "middle" state like run_wait and enable_wait, we make sure that the timer is in a safe state before we start/stop it. And if the state is invalid, it can return an error code to the user.