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| <div class="section" id="apache-mynewt-operating-system-kernel"> |
| <h1>Apache Mynewt Operating System Kernel<a class="headerlink" href="#apache-mynewt-operating-system-kernel" title="Permalink to this headline">¶</a></h1> |
| <div class="toctree-wrapper compound"> |
| </div> |
| <p>The Mynewt Core OS is a multitasking, preemptive real-time operating |
| system combining a scheduler with typical RTOS features such as mutexes, |
| semaphores, memory pools, etc. The Mynewt Core OS also provides a number |
| of useful utilities such as a task watchdog, networking stack memory |
| buffers and time management API. Each of these features is described in |
| detail in its own section of the manual.</p> |
| <p>A multitasking, preemptive operating system is one in which a number of |
| different tasks can be instantiated and assigned a priority, with higher |
| priority tasks running before lower priority tasks. Furthermore, if a |
| lower priority task is running and a higher priority task wants to run, |
| the lower priority task is halted and the higher priority task is |
| allowed to run. In other words, the lower priority task is preempted by |
| the higher priority task.</p> |
| <div class="section" id="why-use-an-os"> |
| <h2>Why use an OS?<a class="headerlink" href="#why-use-an-os" title="Permalink to this headline">¶</a></h2> |
| <p>You may ask yourself “why do I need a multitasking preemptive OS”? The |
| answer may indeed be that you do not. Some applications are simple and |
| only require a polling loop. Others are more complex and may require |
| that certain jobs are executed in a timely manner or before other jobs |
| are executed. If you have a simple polling loop, you cannot move on to |
| service a job until the current job is done being serviced. With the |
| Mynewt OS, the application developer need not worry about certain jobs |
| taking too long or not executing in a timely fashion; the OS provides |
| mechanisms to deal with these situations. Another benefit of using an OS |
| is that it helps shield application developers from other application |
| code being written; the developer does not have to worry (or has to |
| worry less) about other application code behaving badly and causing |
| undesirable behavior or preventing their code from executing properly. |
| Other benefits of using an OS (and the Mynewt OS in particular) is that |
| it also provides features that the developer would otherwise need to |
| create on his/her own.</p> |
| </div> |
| <div class="section" id="core-os-features"> |
| <h2>Core OS Features<a class="headerlink" href="#core-os-features" title="Permalink to this headline">¶</a></h2> |
| <ul class="simple"> |
| <li><p><a class="reference internal" href="context_switch/context_switch.html"><span class="doc">Scheduler/context switching</span></a></p></li> |
| <li><p><a class="reference internal" href="time/os_time.html"><span class="doc">Time</span></a></p></li> |
| <li><p><a class="reference internal" href="task/task.html"><span class="doc">Tasks</span></a></p></li> |
| <li><p><a class="reference internal" href="event_queue/event_queue.html"><span class="doc">Event queues/callouts</span></a></p></li> |
| <li><p><a class="reference internal" href="semaphore/semaphore.html"><span class="doc">Semaphores</span></a></p></li> |
| <li><p><a class="reference internal" href="mutex/mutex.html"><span class="doc">Mutexes</span></a></p></li> |
| <li><p><a class="reference internal" href="memory_pool/memory_pool.html"><span class="doc">Memory pools</span></a></p></li> |
| <li><p><a class="reference internal" href="heap/heap.html"><span class="doc">Heap</span></a></p></li> |
| <li><p><a class="reference internal" href="mbuf/mbuf.html"><span class="doc">Mbufs</span></a></p></li> |
| <li><p><a class="reference internal" href="sanity/sanity.html"><span class="doc">Sanity</span></a></p></li> |
| <li><p><a class="reference internal" href="callout/callout.html"><span class="doc">Callouts</span></a></p></li> |
| <li><p><a class="reference internal" href="porting/port_os.html"><span class="doc">Porting OS to other platforms</span></a></p></li> |
| </ul> |
| </div> |
| <div class="section" id="basic-os-application-creation"> |
| <h2>Basic OS Application Creation<a class="headerlink" href="#basic-os-application-creation" title="Permalink to this headline">¶</a></h2> |
| <p>Creating an application using the Mynewt Core OS is a relatively simple |
| task. The main steps are:</p> |
| <ol class="arabic simple"> |
| <li><p>Install the basic Newt Tool structure (build structure) for your |
| application.</p></li> |
| <li><p>Create your BSP (Board Support Package).</p></li> |
| <li><p>In your application <code class="docutils literal notranslate"><span class="pre">main()</span></code> function, call the <code class="docutils literal notranslate"><span class="pre">sysinit()</span></code> |
| function to initialize the system and packages, perform application |
| specific initialization, then wait and dispatch events from the OS |
| default event queue in an infinite loop. (See <a class="reference internal" href="../modules/sysinitconfig/sysinitconfig.html"><span class="doc">Compile-Time Configuration and Initialization</span></a> |
| for more details.)</p></li> |
| </ol> |
| <p>Initializing application modules and tasks can get somewhat complicated |
| with RTOS’s similar to Mynewt. Care must be taken that the API provided |
| by a task are initialized prior to being called by another (higher |
| priority) task.</p> |
| <p>For example, take a simple application with two tasks (tasks 1 and 2, |
| with task 1 higher priority than task 2). Task 2 provides an API which |
| has a semaphore lock and this semaphore is initialized by task 2 when |
| the task handler for task 2 is called. Task 1 is expected to call this |
| API.</p> |
| <p>Consider the sequence of events when the OS is started. The scheduler |
| starts running and picks the highest priority task (task 1 in this |
| case). The task handler function for task 1 is called and will keep |
| running until it yields execution. Before yielding, code in the task 1 |
| handler function calls the API provided by task 2. The semaphore being |
| accessed in the task 2 API has yet to be initialized since the task 2 |
| handler function has not had a chance to run! This will lead to |
| undesirable behavior and will need to be addressed by the application |
| developer. Note that the Mynewt OS does guard against internal API being |
| called before the OS has started (they will return error) but it does |
| not safeguard application defined objects from access prior to |
| initialization.</p> |
| </div> |
| <div class="section" id="example"> |
| <h2>Example<a class="headerlink" href="#example" title="Permalink to this headline">¶</a></h2> |
| <p>One way to avoid initialization issues like the one described above is |
| for the application to initialize the objects that are accessed by |
| multiple tasks before it initializes the tasks with the OS.</p> |
| <p>The code example shown below illustrates this concept. The application |
| initializes system and packages, calls an application specific “task |
| initialization” function, and dispatches events from the default event |
| queue. The application task initialization function is responsible for |
| initializing all the data objects that each task exposes to the other |
| tasks. The tasks themselves are also initialized at this time (by |
| calling <a class="reference internal" href="task/task.html#c.os_task_init" title="os_task_init"><code class="xref c c-func docutils literal notranslate"><span class="pre">os_task_init()</span></code></a>).</p> |
| <p>In the example, each task works in a ping-pong like fashion: task 1 |
| wakes up, adds a token to semaphore 1 and then waits for a token from |
| semaphore 2. Task 2 waits for a token on semaphore 1 and once it gets |
| it, adds a token to semaphore 2. Notice that the semaphores are |
| initialized by the application specific task initialization functions |
| and not inside the task handler functions. If task 2 (being lower in |
| priority than task 1) had called <a class="reference internal" href="semaphore/semaphore.html#c.os_sem_init" title="os_sem_init"><code class="xref c c-func docutils literal notranslate"><span class="pre">os_sem_init()</span></code></a> for task2_sem inside |
| task2_handler(), task 1 would have called <a class="reference internal" href="semaphore/semaphore.html#c.os_sem_pend" title="os_sem_pend"><code class="xref c c-func docutils literal notranslate"><span class="pre">os_sem_pend()</span></code></a> using |
| task2_sem before task2_sem was initialized.</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">os_sem</span><span class="w"> </span><span class="n">task1_sem</span><span class="p">;</span> |
| <span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">os_sem</span><span class="w"> </span><span class="n">task2_sem</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="cm">/* Task 1 handler function */</span> |
| <span class="w"> </span><span class="kt">void</span> |
| <span class="w"> </span><span class="nf">task1_handler</span><span class="p">(</span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">arg</span><span class="p">)</span> |
| <span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="cm">/* Release semaphore to task 2 */</span> |
| <span class="w"> </span><span class="n">os_sem_release</span><span class="p">(</span><span class="o">&</span><span class="n">task1_sem</span><span class="p">);</span> |
| |
| <span class="w"> </span><span class="cm">/* Wait for semaphore from task 2 */</span> |
| <span class="w"> </span><span class="n">os_sem_pend</span><span class="p">(</span><span class="o">&</span><span class="n">task2_sem</span><span class="p">,</span><span class="w"> </span><span class="n">OS_TIMEOUT_NEVER</span><span class="p">);</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="w"> </span><span class="p">}</span> |
| |
| <span class="w"> </span><span class="cm">/* Task 2 handler function */</span> |
| <span class="w"> </span><span class="kt">void</span> |
| <span class="w"> </span><span class="nf">task2_handler</span><span class="p">(</span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">arg</span><span class="p">)</span> |
| <span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">os_task</span><span class="w"> </span><span class="o">*</span><span class="n">t</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="cm">/* Wait for semaphore from task1 */</span> |
| <span class="w"> </span><span class="n">os_sem_pend</span><span class="p">(</span><span class="o">&</span><span class="n">task1_sem</span><span class="p">,</span><span class="w"> </span><span class="n">OS_TIMEOUT_NEVER</span><span class="p">);</span> |
| |
| <span class="w"> </span><span class="cm">/* Release task2 semaphore */</span> |
| <span class="w"> </span><span class="n">os_sem_release</span><span class="p">(</span><span class="o">&</span><span class="n">task2_sem</span><span class="p">);</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="w"> </span><span class="p">}</span> |
| |
| |
| <span class="w"> </span><span class="cm">/* Initialize task 1 exposed data objects */</span> |
| <span class="w"> </span><span class="kt">void</span> |
| <span class="w"> </span><span class="nf">task1_init</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> |
| <span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="cm">/* Initialize task1 semaphore */</span> |
| <span class="w"> </span><span class="n">os_sem_init</span><span class="p">(</span><span class="o">&</span><span class="n">task1_sem</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">);</span> |
| <span class="w"> </span><span class="p">}</span> |
| |
| <span class="w"> </span><span class="cm">/* Initialize task 2 exposed data objects */</span> |
| <span class="w"> </span><span class="kt">void</span> |
| <span class="w"> </span><span class="nf">task2_init</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> |
| <span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="cm">/* Initialize task1 semaphore */</span> |
| <span class="w"> </span><span class="n">os_sem_init</span><span class="p">(</span><span class="o">&</span><span class="n">task2_sem</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">);</span> |
| <span class="w"> </span><span class="p">}</span> |
| |
| <span class="w"> </span><span class="cm">/**</span> |
| <span class="cm"> * init_app_tasks</span> |
| <span class="cm"> *</span> |
| <span class="cm"> * This function performs initializations that are required before tasks run.</span> |
| <span class="cm"> *</span> |
| <span class="cm"> * @return int 0 success; error otherwise.</span> |
| <span class="cm"> */</span> |
| <span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kt">int</span> |
| <span class="w"> </span><span class="nf">init_app_tasks</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> |
| <span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="cm">/*</span> |
| <span class="cm"> * Call task specific initialization functions to initialize any shared objects</span> |
| <span class="cm"> * before initializing the tasks with the OS.</span> |
| <span class="cm"> */</span> |
| <span class="w"> </span><span class="n">task1_init</span><span class="p">();</span> |
| <span class="w"> </span><span class="n">task2_init</span><span class="p">();</span> |
| |
| <span class="w"> </span><span class="cm">/*</span> |
| <span class="cm"> * Initialize tasks 1 and 2 with the OS.</span> |
| <span class="cm"> */</span> |
| <span class="w"> </span><span class="n">os_task_init</span><span class="p">(</span><span class="o">&</span><span class="n">task1</span><span class="p">,</span><span class="w"> </span><span class="s">"task1"</span><span class="p">,</span><span class="w"> </span><span class="n">task1_handler</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span><span class="p">,</span><span class="w"> </span><span class="n">TASK1_PRIO</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">OS_WAIT_FOREVER</span><span class="p">,</span><span class="w"> </span><span class="n">task1_stack</span><span class="p">,</span><span class="w"> </span><span class="n">TASK1_STACK_SIZE</span><span class="p">);</span> |
| |
| <span class="w"> </span><span class="n">os_task_init</span><span class="p">(</span><span class="o">&</span><span class="n">task2</span><span class="p">,</span><span class="w"> </span><span class="s">"task2"</span><span class="p">,</span><span class="w"> </span><span class="n">task2_handler</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span><span class="p">,</span><span class="w"> </span><span class="n">TASK2_PRIO</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">OS_WAIT_FOREVER</span><span class="p">,</span><span class="w"> </span><span class="n">task2_stack</span><span class="p">,</span><span class="w"> </span><span class="n">TASK2_STACK_SIZE</span><span class="p">);</span> |
| |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span> |
| <span class="w"> </span><span class="p">}</span> |
| |
| <span class="w"> </span><span class="cm">/**</span> |
| <span class="cm"> * main</span> |
| <span class="cm"> *</span> |
| <span class="cm"> * The main function for the application. This function initializes the system and packages,</span> |
| <span class="cm"> * calls the application specific task initialization function, then waits and dispatches</span> |
| <span class="cm"> * events from the OS default event queue in an infinite loop.</span> |
| <span class="cm"> */</span> |
| <span class="w"> </span><span class="kt">int</span> |
| <span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">**</span><span class="n">arg</span><span class="p">)</span> |
| <span class="w"> </span><span class="p">{</span> |
| |
| <span class="w"> </span><span class="cm">/* Perform system and package initialization */</span> |
| <span class="w"> </span><span class="n">sysinit</span><span class="p">();</span> |
| |
| <span class="w"> </span><span class="cm">/* Initialize application specific tasks */</span> |
| <span class="w"> </span><span class="n">init_app_tasks</span><span class="p">();</span> |
| |
| <span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="n">os_eventq_run</span><span class="p">(</span><span class="n">os_eventq_dflt_get</span><span class="p">());</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="w"> </span><span class="cm">/* main never returns */</span> |
| <span class="p">}</span> |
| </pre></div> |
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