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esp-idf/components/driver/gptimer/README.md
morris 2d52334e5d gptimer: fix race condition between start and stop 
Added state transition in gptimer_start/stop functions.
So that it's not possible to make a stopped timer continue to run
because of race condition.
2023-03-10 23:27:29 +08:00

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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.