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| <section id="microchip-da-db-family"> |
| <h1>Microchip DA/DB family<a class="headerlink" href="#microchip-da-db-family" title="Permalink to this heading"></a></h1> |
| <p>This is an attempt to support AVR DA/DB family of MCUs</p> |
| <section id="supported-chips"> |
| <h2>Supported chips<a class="headerlink" href="#supported-chips" title="Permalink to this heading"></a></h2> |
| <p>The code was developed using AVR128DA28 MCU on a breadboard. Currently, |
| all testing was done with that chip. The chips in DA family are quite |
| similar, the main differences are pin count and flash size. (Pin count |
| also corresponds to supported peripherals, chips with more pins have |
| more instances of the same peripheral, eg. more USARTs.)</p> |
| <p>Chips in DB family are fairly similar to DA as well, |
| some peripherals are missing, some features are added.</p> |
| <p>This means that support for other chips is fairly easy to add, |
| all that is needed is to provide interrupt vector definitions |
| and similar data describing the chip. All architecture code should |
| otherwise be written in a way to automatically support the chip.</p> |
| <p>Currently, <code class="docutils literal notranslate"><span class="pre">AVR128DA64</span></code> and <code class="docutils literal notranslate"><span class="pre">AVR128DB64</span></code> chips are supported |
| this way (ie. definitions describing the chip are provided |
| but there is no board.)</p> |
| </section> |
| <section id="clock-configuration"> |
| <h2>Clock Configuration<a class="headerlink" href="#clock-configuration" title="Permalink to this heading"></a></h2> |
| <p>The chip features internal high frequency oscillator, its frequency |
| can be set in the Kconfig-based configuration. Clock speed in MHz |
| is then provided in CONFIG_AVRDX_HFO_CLOCK_FREQ</p> |
| </section> |
| <section id="system-timer"> |
| <h2>System Timer<a class="headerlink" href="#system-timer" title="Permalink to this heading"></a></h2> |
| <p>System timer is provided by RTC peripheral and takes over it. (In theory, |
| the Periodic Interrupt - PIT - component of it can be still used |
| but they share single clock.)</p> |
| <p>Tickless OS mode is supported in alarm mode. Configure it |
| in <span class="menuselection">RTOS Features ‣ Clocks and Timers ‣ Support tick-less OS</span> |
| <span class="menuselection">Tickless alarm</span> must be set, timer mode is not supported. |
| <span class="menuselection">System timer tick period (microseconds)</span> also needs to be |
| changed to value of at least 300. Higher value is recommended though, |
| 300us is not going to be precise at all.</p> |
| </section> |
| <section id="peripheral-support"> |
| <h2>Peripheral Support<a class="headerlink" href="#peripheral-support" title="Permalink to this heading"></a></h2> |
| <p>The following list indicates peripherals supported in NuttX:</p> |
| <table class="docutils align-default"> |
| <thead> |
| <tr class="row-odd"><th class="head"><p>Peripheral</p></th> |
| <th class="head"><p>Notes</p></th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr class="row-even"><td><p>GPIO</p></td> |
| <td><p>In board code</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>UART</p></td> |
| <td><p>See below</p></td> |
| </tr> |
| <tr class="row-even"><td><p>TWI</p></td> |
| <td><p>Master only, more below</p></td> |
| </tr> |
| </tbody> |
| </table> |
| <section id="gpio"> |
| <h3>GPIO<a class="headerlink" href="#gpio" title="Permalink to this heading"></a></h3> |
| <p>For the most part, there is no need for any specific support for GPIO |
| in architecture code. For example, NuttX button input driver should only |
| need functions defined in the board code to work.</p> |
| <p>The architecture code provides means to share single interrupt vector |
| if the board needs to have multiple peripherals connected to a single |
| I/O port. See gpio_intr_mux.rst for details and breadxavr board |
| for example usage.</p> |
| </section> |
| <section id="uart"> |
| <h3>UART<a class="headerlink" href="#uart" title="Permalink to this heading"></a></h3> |
| <p>UART is implemented using interrupts. The chip doesn’t support DMA. |
| From some initial testing done using simple echo (read/write) loop |
| it seems the driver cannot handle sustained data transmission |
| with baud rate higher than 57600 even with the chip running at its |
| highest speed. With baud rate 57600, performance was dependent |
| on read/write buffer size. With buffer size of 8 there were still |
| some missed bytes.</p> |
| <p>To be able to use standard serial driver, it is needed to enable |
| the peripheral in MCU-specific configuration in |
| <span class="menuselection">System Type ‣ AVR DA/DB Peripheral Selections</span> |
| UART peripherals are enabled using |
| <span class="menuselection">Enable serial driver for USARTn</span> options. When enabled, |
| additional option <span class="menuselection">Activate USART0 alternative pinout</span> |
| is provided. See the chip datasheet for pinout information.</p> |
| <p>Other UART settings are then configured in driver configuration |
| <span class="menuselection">Device Drivers ‣ Serial Driver Support</span> |
| For every enabled peripheral, there is a corresponding |
| <span class="menuselection">USARTn Configuration</span> section. RTS/CTS and DMA support |
| must NOT be enabled here, neither of those is supported.</p> |
| <p>Each enabled peripheral is automatically registered as <code class="docutils literal notranslate"><span class="pre">/dev/ttySn</span></code> |
| device file. File name corresponds to the peripheral related to it. |
| This for example means that <code class="docutils literal notranslate"><span class="pre">USART1</span></code> peripheral will always |
| be accessed through <code class="docutils literal notranslate"><span class="pre">/dev/ttyS1</span></code> regardless of what other <code class="docutils literal notranslate"><span class="pre">USART</span></code> |
| peripherals are enabled (if any.)</p> |
| </section> |
| <section id="twi"> |
| <h3>TWI<a class="headerlink" href="#twi" title="Permalink to this heading"></a></h3> |
| <p>Currently, only master is supported. Implementation details and quick |
| usage instructions can be found in <a class="reference internal" href="docs/twi.html"><span class="doc">Two Wire Interface in AVR DA/DB</span></a> document.</p> |
| </section> |
| </section> |
| <section id="supported-boards"> |
| <h2>Supported Boards<a class="headerlink" href="#supported-boards" title="Permalink to this heading"></a></h2> |
| <div class="toctree-wrapper compound"> |
| <ul> |
| <li class="toctree-l1"><a class="reference internal" href="boards/breadxavr/index.html">AVR128DA28 on breadboard</a></li> |
| </ul> |
| </div> |
| </section> |
| <section id="other-documents"> |
| <h2>Other documents<a class="headerlink" href="#other-documents" title="Permalink to this heading"></a></h2> |
| <div class="toctree-wrapper compound"> |
| <ul> |
| <li class="toctree-l1"><a class="reference internal" href="docs/gpio_intr_mux.html">GPIO interrupt multiplexer</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="docs/twi.html">Two Wire Interface in AVR DA/DB</a></li> |
| </ul> |
| </div> |
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