Module: xenomai-forge
Branch: master
Commit: 331d69476ea89e5d92e4b2c2ef8ba6e0aaad5f1b
URL:    
http://git.xenomai.org/?p=xenomai-forge.git;a=commit;h=331d69476ea89e5d92e4b2c2ef8ba6e0aaad5f1b

Author: Philippe Gerum <r...@xenomai.org>
Date:   Sun Sep 28 17:03:44 2014 +0200

alchemy/timer: drop TSC reading and conversion ops from the API

Due to the accumulation of rounding errors, using raw TSC counts for
measuring long timespans may yield (increasingly) wrong results.

In short, either we guarantee stable computations with counts of
nanoseconds, or with TSC instead, regardless of the clock source
frequency, but we can't provide such guarantee for both. From an API
standpoint, the nanosecond unit is definitely the best option as the
meaning won't vary between clock sources.

Avoiding the overhead of the tsc->ns conversion as a justification to
use raw TSC counts does not fly anymore, as all architectures
implement fast arithmetics for this operation over Cobalt, and
Mercury's (virtual) TSC is actually mapped over CLOCK_MONOTONIC.

Therefore, all TSC reading and ns<->tsc conversion services are
removed from the Alchemy API to prevent misleading results. Users
should measure timespans (or get timestamps) as counts of nanoseconds
as returned by rt_timer_read() instead.

The following calls are dropped from the API:

- rt_timer_tsc()
- rt_timer_ns2tsc()
- rt_timer_tsc2ns()

In addition, rt_timer_inquire() does not return the TSC count anymore.

---

 include/alchemy/timer.h |   39 ++++++---------------------------------
 lib/alchemy/timer.c     |    9 ++++-----
 2 files changed, 10 insertions(+), 38 deletions(-)

diff --git a/include/alchemy/timer.h b/include/alchemy/timer.h
index 5c1cc08..7b3837b 100644
--- a/include/alchemy/timer.h
+++ b/include/alchemy/timer.h
@@ -38,8 +38,8 @@ typedef sticks_t SRTIME;
  * @brief Timer status descriptor
  * @anchor RT_TIMER_INFO
  *
- * This structure reports various static and runtime information about
- * the timer, returned by a call to rt_timer_inquire().
+ * This structure reports information about the Alchemy clock,
+ * returned by a call to rt_timer_inquire().
  */
 typedef struct rt_timer_info {
        /**
@@ -47,22 +47,10 @@ typedef struct rt_timer_info {
         */
        RTIME period;
        /**
-        * Current time stamp counter value. The source of this
-        * information is hardware-dependent, and does not depend on
-        * the per-process clock settings. Consecutive readings from a
-        * single CPU are guaranteed to be monotonically incrementing,
-        * however readings may not be synchronized on multi-core
-        * hardware if the time stamp counter is local to each CPU.
-        * Therefore, whether consecutive readings from different CPUs
-        * are consistent and monotonically incrementing depends on
-        * the underlying TSC source.
-        */
-       RTIME tsc;
-       /**
-        * Current monotonic date, based on the time stamp counter
-        * value. The date is expressed in clock ticks, therefore
-        * depends on the Alchemy clock resolution applicable to the
-        * current process.
+        * Current monotonic date expressed in clock ticks. The
+        * duration of a tick depends on the Alchemy clock resolution
+        * for the process (see --alchemy-clock-resolution option,
+        * defaults to 1 nanosecond).
         */
        RTIME date;
 } RT_TIMER_INFO;
@@ -118,21 +106,6 @@ static inline RTIME rt_timer_read(void)
        return clockobj_get_time(&alchemy_clock);
 }
 
-static inline RTIME rt_timer_tsc(void)
-{
-       return clockobj_get_tsc();
-}
-
-static inline SRTIME rt_timer_ns2tsc(SRTIME ns)
-{
-       return clockobj_ns_to_tsc(ns);
-}
-
-static inline SRTIME rt_timer_tsc2ns(SRTIME tsc)
-{
-       return clockobj_tsc_to_ns(tsc);
-}
-
 SRTIME rt_timer_ns2ticks(SRTIME ns);
 
 SRTIME rt_timer_ticks2ns(SRTIME ticks);
diff --git a/lib/alchemy/timer.c b/lib/alchemy/timer.c
index d37a9d7..7c08233 100644
--- a/lib/alchemy/timer.c
+++ b/lib/alchemy/timer.c
@@ -76,12 +76,12 @@ SRTIME rt_timer_ticks2ns(SRTIME ticks)
 
 /**
  * @fn void rt_timer_inquire(RT_TIMER_INFO *info)
- * @brief Inquire about the Xenomai core timer.
+ * @brief Inquire about the Alchemy clock.
  *
- * Return status information of the Xenomai core timer.
+ * Return status information about the Alchemy clock.
  *
- * @param info The address of a structure the status data will be
- * written to.
+ * @param info The address of a @ref RT_TIMER_INFO "structure" to fill
+ * with the clock information.
  *
  * @apitags{unrestricted}
  */
@@ -89,7 +89,6 @@ void rt_timer_inquire(RT_TIMER_INFO *info)
 {
        info->period = clockobj_get_resolution(&alchemy_clock);
        info->date = clockobj_get_time(&alchemy_clock);
-       info->tsc = clockobj_get_tsc();
 }
 
 /**


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