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doc: Add clarification to common execution contexts docs

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A couple paragraphs contain ambiguous verbs that are unclear.
(For example: Line 23. Does the kernel perform a busy-wait,
or does it merely permit a task or fiber to perform a busy-wait?)
Based on original, I guess the latter and attempted to correct this
in the docs.

Also fixed spelling error.

Change-Id: I0699835a9681c1a4873575fbf9a69bc6d854bee4
Signed-off-by: L.S. Cook <leonax.cook@intel.com>
This commit is contained in:
L.S. Cook 2016-02-22 11:36:51 -08:00 • committed by Gerrit Code Review
commit 32fd061e66
1 changed files with 25 additions and 24 deletions
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49
doc/kernel/common/common_contexts.rst
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@ -6,36 +6,36 @@ Execution Context Services
Concepts
********
Each kernel execution context has an associated *type*, which indicates whether
Every kernel execution context has an associated *type* that indicates whether
the context is a task, a fiber, or the kernel's interrupt handling context.
Task and fiber contexts also have an associated *thread identifier* value,
which is used to uniquely identify these threads.
Each task and fiber may also support a 32-bit *thread custom data* value.
This value is accessible only by the task or fiber itself, and can be used
by the application for any purpose. The default custom data value for a
task or fiber is zero.
All task and fiber contexts have a unique *thread identifier* value used to
uniquely identify them. Each task and fiber can also support a 32-bit *thread
custom data* value. This value is accessible only by the task or fiber itself,
and may be used by the application for any purpose. The default custom data
value for a task or fiber is zero.
.. note::
The custom data value is not available to ISRs, which operate in the shared
kernel interrupt handling context.
The custom data value is not available to ISRs because these operate
only within the shared kernel interrupt handling context.
The kernel allows a task or fiber to delay its processing for a specified time
period by performing a busy wait. This allows the delay to occur without
requiring the kernel to perform the context switching that occurs with its
more typical timer and timeout services.
The kernel permits a task or a fiber to perform a ``busy wait``, thus delaying
its processing for a specified time period. Such a delay occurs without
requiring the kernel to perform context switching, as it typically does with
timer and timeout services.
Purpose
*******
Use the kernel execution context services when writing code that needs to
operate differently when executed by different contexts.
Use kernel execution context services when writing code that should
operate differently when it is executed by different contexts.
Use the busy wait service when the required delay is too short to warrant
context switching to another task or fiber, or when performing a delay
as part of the nanokernel's background task (which is not allowed to
volutarily relinquish the CPU).
Use the ``busy wait`` service when the required delay is too short to
warrant context switching to another task or fiber. The ``busy wait``
service may also be used when performing a delay as part of the
nanokernel's background task in a nanokernel-only system; this task is
not allowed to voluntarily relinquish the CPU.
Usage
@ -51,10 +51,11 @@ support is disabled.
Example: Performing Execution Context-Specific Processing
=========================================================
This code shows how a routine can use a thread's custom data value
to limit the number of times a thread may call the routine.
Counting is not performed when the routine is called by an ISR, which does not
have a custom data value.
to limit the number of times a thread may call the routine. Note that
counting is not performed when the routine is called by an ISR; ISRs
do not have a custom data value.
.. note::
Obviously, only a single routine can use this technique
@ -83,8 +84,8 @@ have a custom data value.
APIs
****
The following kernel execution context APIs are provided by
:file:`microkernel.h` and by :file:`nanokernel.h`:
The following kernel execution context APIs are common to both
:file:`microkernel.h` and :file:`nanokernel.h`:
:c:func:`sys_thread_self_get()`