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authorSebastian Huber <sebastian.huber@embedded-brains.de>2017-01-30 14:22:14 +0100
committerSebastian Huber <sebastian.huber@embedded-brains.de>2017-01-30 14:22:14 +0100
commit1161ed179c0be212b7909d6a761bfc31cacf4ca3 (patch)
tree3dfc2e393426be12060bb00fbc508058b32d9537 /c-user/timer_manager.rst
parenta17535d222a1268542e97c7e6c1b2fdf045e46d8 (diff)
downloadrtems-docs-1161ed179c0be212b7909d6a761bfc31cacf4ca3.tar.bz2
c-user: Update timer manager
Update #2554.
Diffstat (limited to 'c-user/timer_manager.rst')
-rw-r--r--c-user/timer_manager.rst24
1 files changed, 16 insertions, 8 deletions
diff --git a/c-user/timer_manager.rst b/c-user/timer_manager.rst
index 000348d..1e29add 100644
--- a/c-user/timer_manager.rst
+++ b/c-user/timer_manager.rst
@@ -65,9 +65,10 @@ Timer Server
------------
The Timer Server task is responsible for executing the timer service routines
-associated with all task-based timers. This task executes at a priority higher
-than any RTEMS application task, and is created non-preemptible, and thus can
-be viewed logically as the lowest priority interrupt.
+associated with all task-based timers. This task executes at a priority
+specified by :ref:`rtems_timer_initiate_server() <rtems_timer_initiate_server>`
+and it may have a priority of zero (the highest priority). In uni-processor
+configurations, it is created non-preemptible.
By providing a mechanism where timer service routines execute in task rather
than interrupt space, the application is allowed a bit more flexibility in what
@@ -75,9 +76,10 @@ operations a timer service routine can perform. For example, the Timer Server
can be configured to have a floating point context in which case it would be
safe to perform floating point operations from a task-based timer. Most of the
time, executing floating point instructions from an interrupt service routine
-is not considered safe. However, since the Timer Server task is
-non-preemptible, only directives allowed from an ISR can be called in the timer
-service routine.
+is not considered safe. The timer service routines invoked by the Timer Server
+may block, however, since this blocks the Timer Server itself, other timer
+service routines that are already pending do not run until the blocked timer
+service routine finished its work.
The Timer Server is designed to remain blocked until a task-based timer fires.
This reduces the execution overhead of the Timer Server.
@@ -227,7 +229,12 @@ DESCRIPTION:
local TMCB free pool and initializes it.
NOTES:
- This directive will not cause the calling task to be preempted.
+ This directive will obtain the allocator mutex and may cause the calling
+ task to be preempted.
+
+ In SMP configurations, the processor of the currently executing thread
+ determines the processor used for the created timer. During the life-time
+ of the timer this processor is used to manage the timer internally.
.. raw:: latex
@@ -337,7 +344,8 @@ DESCRIPTION:
by RTEMS.
NOTES:
- This directive will not cause the running task to be preempted.
+ This directive will obtain the allocator mutex and may cause the calling
+ task to be preempted.
A timer can be deleted by a task other than the task which created the
timer.