wangchdo opened a new pull request, #17517:
URL: https://github.com/apache/nuttx/pull/17517
## Summary
Per @xiaoxiang781216's suggestion, I have Split #17489 into two parts:
Part 1: Add hrtimer only — this PR.
Part 2: Add hrtimer along with scheduler support — the original PR #17489.
**So the summary of this PR can be(borrowed from #17489 ):**
- Introduce a high-resolution timer (hrtimer) module to NuttX, providing
timers with nanosecond-level resolution.
- Provide three new hrtimer APIs:
1. hrtimer_init() – Initialize a high-resolution timer instance.
2. hrtimer_start() – Start a high-resolution timer in absolute or relative
mode.
3. hrtimer_cancel() – Cancel a pending high-resolution timer.
Per @xiaoxiang781216’s comments, I have updated the critical section
protection for hrtimer to use a spinlock to improve performance.
However, to prevent potential issues where hrtimer_cancel() might cancel a
running timer and the timer instance could be freed prematurely, I have
introduced a state machine for hrtimer:
```
INACTIVE
|
| start
v
ARMED -------- cancel --------> CANCELED
| ^
| expire |
v |
RUNNING -------- cancel ----------+
|
| return
v
INACTIVE
```
**Key points:**
1. hrtimer_cancel() remains non-blocking.
2. If the timer callback is currently executing, it is allowed to complete.
3. After cancellation, the callback will not be invoked again.
4. The caller must ensure that timer-related resources are not freed until
the callback has returned.
## Impact
Add a new high-resolution timer (hrtimer) module to NuttX.
## Testing
**ostest passed on a2g-tc397-5v-tft with hrtimer enalbed**
```
nsh> uname -a
NuttX 0.0.0 169028d7be Dec 16 2025 10:39:58 tricore a2g-tc397-5v-tft
nsh>
nsh> ostest
(...)
user_main: hrtimer test
End of test memory usage:
VARIABLE BEFORE AFTER
======== ======== ========
arena 28dfc 28dfc
ordblks 6 6
mxordblk 1f8a8 1f8a8
uordblks 555c 555c
fordblks 238a0 238a0
Final memory usage:
VARIABLE BEFORE AFTER
======== ======== ========
arena 28dfc 28dfc
ordblks 1 6
mxordblk 24220 1f8a8
uordblks 4bdc 555c
fordblks 24220 238a0
user_main: Exiting
ostest_main: Exiting with status 0
```
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