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| <div class="section" id="drivers"> |
| <h1>Drivers<a class="headerlink" href="#drivers" title="Permalink to this headline">¶</a></h1> |
| <div class="toctree-wrapper compound"> |
| </div> |
| <div class="section" id="description"> |
| <h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2> |
| <p>Device drivers in the Mynewt context includes libraries that interface |
| with devices external to the CPU. These devices are connected to the CPU |
| via standard peripherals such as SPI, GPIO, I2C etc. Device drivers |
| leverage the base HAL services in Mynewt to provide friendly |
| abstractions to application developers.</p> |
| <div class="highlight-console notranslate"><div class="highlight"><pre><span></span><span class="go">+———————————————————————————+</span> |
| <span class="go">| app |</span> |
| <span class="go">+———————————————————————————+</span> |
| <span class="go">| (n)drivers |</span> |
| <span class="go">+———————————————————————————+</span> |
| <span class="go">| HAL | BSP |</span> |
| <span class="go">+—————————————+—————————————+</span> |
| </pre></div> |
| </div> |
| <ul class="simple"> |
| <li><p>The Board Support Package (BSP) abstracts board specific |
| configurations e.g. CPU frequency, input voltage, LED pins, on-chip |
| flash map etc.</p></li> |
| <li><p>The Hardware Abstraction Layer (HAL) abstracts architecture-specific |
| functionality. It initializes and enables components within a master |
| processor. It is designed to be portable across all the various MCUs |
| supported in Mynewt (e.g. Nordic’s nRF51, Nordic’s nRF52, NXP’s |
| MK64F12 etc.). It includes code that initializes and manages access |
| to components of the board such as board buses (I2C, PCI, PCMCIA, |
| etc.), off-chip memory (controllers, level 2+ cache, Flash, etc.), |
| and off-chip I/O (Ethernet, RS-232, display, mouse, etc.)</p></li> |
| <li><p>The driver sits atop the BSP and HAL. It abstracts the common modes |
| of operation for each peripheral device connected via the standard |
| interfaces to the processor. There may be multiple driver |
| implementations of differing complexities for a particular peripheral |
| device. For example, for an Analog to Digital Converter (ADC) |
| peripheral you might have a simple driver that does blocking ADC |
| reads and uses the HAL only. You might have a more complex driver |
| that can deal with both internal and external ADCs, and has chip |
| specific support for doing things like DMA’ing ADC reads into a |
| buffer and posting an event to a task every ’n’ samples. The drivers |
| are the ones that register with the kernel’s power management APIs, |
| and manage turning on and off peripherals and external chipsets, etc. |
| The Mynewt core repository comes with a base set of drivers to help |
| the user get started.</p></li> |
| </ul> |
| </div> |
| <div class="section" id="general-design-principles"> |
| <h2>General design principles<a class="headerlink" href="#general-design-principles" title="Permalink to this headline">¶</a></h2> |
| <ul class="simple"> |
| <li><p>Device drivers should have a consistent structure and unified |
| interface whenever possible. For example, we have a top-level |
| package, “adc”, which contains the interface for all ADC drivers, and |
| then we have the individual implementation of the driver itself. The |
| following source files point to this:</p> |
| <ul> |
| <li><p>high-level ADC API: <code class="docutils literal notranslate"><span class="pre">hw/drivers/adc/include/adc/adc.h</span></code></p></li> |
| <li><p>implementation of ADC for STM32F4: |
| <code class="docutils literal notranslate"><span class="pre">hw/drivers/adc/adc_stm32f4/src/adc_stm32f4.c</span></code> (As of the |
| 1.0.0-beta release, ADC for nRF51 and nRF52 are available at an |
| external |
| <a class="reference external" href="https://github.com/runtimeco/mynewt_nordic/tree/master/hw/drivers/adc">repo</a>. |
| They are expected to be pulled into the core repo on Apache Mynewt |
| after the license terms are clarified.). The only exported call in |
| this example is |
| <code class="docutils literal notranslate"><span class="pre">int</span> <span class="pre">stm32f4_adc_dev_init(struct</span> <span class="pre">os_dev</span> <span class="pre">*,</span> <span class="pre">void</span> <span class="pre">*)</span></code> which is |
| passed as a function pointer to <code class="docutils literal notranslate"><span class="pre">os_dev_create()</span></code> in |
| <code class="docutils literal notranslate"><span class="pre">hal_bsp.c</span></code>, when the adc device is created.</p></li> |
| </ul> |
| </li> |
| <li><p>Device drivers should be easy to use. In Mynewt, creating a device |
| initializes it as well, making it readily available for the user to |
| open, use (e.g. read, configure etc.) and close. Creating a device is |
| simple using |
| <code class="docutils literal notranslate"><span class="pre">os_dev_create(struct</span> <span class="pre">os_dev</span> <span class="pre">*dev,</span> <span class="pre">char</span> <span class="pre">*name,</span> <span class="pre">uint8_t</span> <span class="pre">stage,</span> <span class="pre">uint8_t</span> <span class="pre">priority,</span> <span class="pre">os_dev_init_func_t</span> <span class="pre">od_init,</span> <span class="pre">void</span> <span class="pre">*arg)</span></code>. |
| The <code class="docutils literal notranslate"><span class="pre">od_init</span></code> function is defined within the appropriate driver |
| directory e.g. <code class="docutils literal notranslate"><span class="pre">stm32f4_adc_dev_init</span></code> in |
| <code class="docutils literal notranslate"><span class="pre">hw/drivers/adc/adc_stm32f4/src/adc_stm32f4.c</span></code> for the ADC device |
| initialization function.</p></li> |
| <li><p>The implementation should allow for builds optimized for minimal |
| memory usage. Additional functionality can be enabled by writing a |
| more complex driver (usually based on the simple implementation |
| included by default in the core repository) and optionally compiling |
| the relevant packages in. Typically, only a basic driver that |
| addresses a device’s core functionality (covering ~90% of use cases) |
| is included in the Mynewt core repository, thus keeping the footprint |
| small.</p></li> |
| <li><p>The implementation should allow a user to be able to instantiate |
| multiple devices of a certain kind. In the Mynewt environment the |
| user can, for example, maintain separate contexts for multiple ADCs |
| over different peripheral connections such as SPI, I2C etc. It is |
| also possible for a user to use a single peripheral interface (e.g. |
| SPI) to drive multiple devices (e.g. ADC), and in that case the |
| device driver has to handle the proper synchronization of the various |
| tasks.</p></li> |
| <li><p>Device drivers should be MCU independent. In Mynewt, device creation |
| and operation functions are independent of the underlying MCU.</p></li> |
| <li><p>Device drivers should be able to offer high-level interfaces for |
| generic operations common to a particular device group. An example of |
| such a class or group of devices is a group for sensors with generic |
| operations such as channel discovery, configure, and read values. The |
| organization of the driver directory is work in progress - so we |
| encourage you to hop on the dev@ mailing list and offer your |
| insights!</p></li> |
| <li><p>Device drivers should be searchable. The plan is to have the newt |
| tool offer a <code class="docutils literal notranslate"><span class="pre">newt</span> <span class="pre">pkg</span> <span class="pre">search</span></code> capability. This is work in |
| progress. You are welcome to join the conversation on the dev@ |
| mailing list!</p></li> |
| </ul> |
| </div> |
| <div class="section" id="example"> |
| <h2>Example<a class="headerlink" href="#example" title="Permalink to this headline">¶</a></h2> |
| <p>The Mynewt core repo includes an example of a driver using the HAL to |
| provide extra functionality - the UART driver. It uses HAL GPIO and UART |
| to provide multiple serial ports on the NRF52 (but allowed on other |
| platforms too.)</p> |
| <p>The gist of the driver design is that there is an API for the driver |
| (for use by applications), and then sub-packages to that driver that |
| implement that driver API using the HAL and BSP APIs.</p> |
| </div> |
| <div class="section" id="implemented-drivers"> |
| <h2>Implemented drivers<a class="headerlink" href="#implemented-drivers" title="Permalink to this headline">¶</a></h2> |
| <p>Drivers live under <code class="docutils literal notranslate"><span class="pre">hw/drivers</span></code>. The current list of supported drivers |
| includes:</p> |
| <table class="docutils align-default"> |
| <colgroup> |
| <col style="width: 61%" /> |
| <col style="width: 39%" /> |
| </colgroup> |
| <thead> |
| <tr class="row-odd"><th class="head"><p>Driver</p></th> |
| <th class="head"><p>Description</p></th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">adc</span></code></p></td> |
| <td><p>TODO: ADC driver.</p></td> |
| </tr> |
| <tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">flash</span></code></p></td> |
| <td><p>SPI/I2C flash drivers.</p></td> |
| </tr> |
| <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">lwip</span></code></p></td> |
| <td><p>TODO: LWIP.</p></td> |
| </tr> |
| <tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">mmc</span></code></p></td> |
| <td><p>MMC/SD card driver.</p></td> |
| </tr> |
| <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">sensors</span></code></p></td> |
| <td><p>TODO: sensors.</p></td> |
| </tr> |
| <tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">uart</span></code></p></td> |
| <td><p>TODO: UART driver.</p></td> |
| </tr> |
| <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">chg_ctrl</span></code></p></td> |
| <td><p>Charge control drivers.</p></td> |
| </tr> |
| </tbody> |
| </table> |
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