| .. | ||
| include | ||
| src | ||
| test_apps | ||
| CMakeLists.txt | ||
| Kconfig | ||
| linker.lf | ||
| README.md | ||
GPTimer Driver Design
State Transition
State transition is achieved by using the primitives provided by
<stdatomic.h>.
stateDiagram-v2
[*] --> init: gptimer_new_timer
init --> enable: gptimer_enable
enable --> init: gptimer_disable
enable --> run: gptimer_start*
run --> enable: gptimer_stop*
init --> [*]: gptimer_del_timer
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.
stateDiagram-v2
state Race-Condition {
Thread --> gptimer_start
state gptimer_start {
state is_enabled <<choice>>
[*] --> is_enabled: Enabled?
is_enabled --> run_wait: yes
is_enabled --> [*] : no
run_wait --> run: call HAL/LL functions to start timer
}
--
Interrupt --> gptimer_stop
state gptimer_stop {
state is_running <<choice>>
[*] --> is_running: Running?
is_running --> enable_wait: yes
is_running --> [*] : no
enable_wait --> enable: call HAL/LL functions to stop timer
}
}
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.