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esp-idf/components/esp_driver_gptimer/README.md

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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.