From b7bcec2d8c06ce8f1797a24d21229bc4b0dc1d28 Mon Sep 17 00:00:00 2001
From: Lorenz Meier <lorenz@px4.io>
Date: Sun, 20 Jan 2019 16:11:52 +0100
Subject: [PATCH] HRT: Create new separate call for atomic HRT elapsed time
calculation This call rarely needs to be truly atomic and the involved CPU
overhead in making it atomic was unnecessary and introduces a lot of IRQ
jitter with no value-add. The call has been moved to be non-atomic and the
codebase will be inspected and changed in follow-up commits for the few
instances where it is truly needed.
---
src/drivers/drv_hrt.h | 10 +++++++++-
src/drivers/stm32/drv_hrt.c | 11 +++++++++++
2 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/src/drivers/drv_hrt.h b/src/drivers/drv_hrt.h
index 19e2456b12..17fe4ba107 100644
--- a/src/drivers/drv_hrt.h
+++ b/src/drivers/drv_hrt.h
@@ -92,6 +92,14 @@ __EXPORT extern hrt_abstime ts_to_abstime(const struct timespec *ts);
*/
__EXPORT extern void abstime_to_ts(struct timespec *ts, hrt_abstime abstime);
+/**
+ * Compute the delta between a timestamp taken in the past
+ * and now.
+ *
+ * This function is not interrupt save.
+ */
+__EXPORT extern hrt_abstime hrt_elapsed_time(const volatile hrt_abstime *then);
+
/**
* Compute the delta between a timestamp taken in the past
* and now.
@@ -99,7 +107,7 @@ __EXPORT extern void abstime_to_ts(struct timespec *ts, hrt_abstime abstime);
* This function is safe to use even if the timestamp is updated
* by an interrupt during execution.
*/
-__EXPORT extern hrt_abstime hrt_elapsed_time(const volatile hrt_abstime *then);
+__EXPORT extern hrt_abstime hrt_elapsed_time_atomic(const volatile hrt_abstime *then);
/**
* Store the absolute time in an interrupt-safe fashion.
diff --git a/src/drivers/stm32/drv_hrt.c b/src/drivers/stm32/drv_hrt.c
index 6fcbbf8e36..f44ad15245 100644
--- a/src/drivers/stm32/drv_hrt.c
+++ b/src/drivers/stm32/drv_hrt.c
@@ -720,6 +720,17 @@ abstime_to_ts(struct timespec *ts, hrt_abstime abstime)
*/
hrt_abstime
hrt_elapsed_time(const volatile hrt_abstime *then)
+{
+ hrt_abstime delta = hrt_absolute_time() - *then;
+
+ return delta;
+}
+
+/**
+ * Compare a time value with the current time as atomic operation
+ */
+hrt_abstime
+hrt_elapsed_time_atomic(const volatile hrt_abstime *then)
{
irqstate_t flags = px4_enter_critical_section();
--
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