81a641d437
since the linker placement of the hal functions are controlled by the Kconfig in the driver component, we should create the linker.lf in the driver component, not in the hal component. |
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|---|---|---|
| .. | ||
| include/driver | ||
| gptimer_etm.c | ||
| gptimer_priv.c | ||
| gptimer_priv.h | ||
| gptimer.c | ||
| 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.