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| <h1 id="hal_spi">hal_spi</h1> |
| <p>SPI (Serial Peripheral Interface) is a synchronous 4-wire serial interface |
| commonly used to connect components in embedded systems.</p> |
| <p>For a detailed description of SPI, see <a href="https://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus">Wikipedia</a>.</p> |
| <h3 id="description">Description</h3> |
| <p>The Mynewt HAL interface supports the SPI master functionality with both blocking and non-blocking interface. SPI slave functionality is supported in non-blocking mode.</p> |
| <h3 id="definition">Definition</h3> |
| <p><a href="https://github.com/apache/incubator-mynewt-core/blob/master/hw/hal/include/hal/hal_spi.h">hal_spi.h</a></p> |
| <h3 id="hal_spi-theory-of-operation">HAL_SPI Theory Of Operation</h3> |
| <p>SPI is called a 4-wire interface because of the 4 signals, MISO, MOSI, CLK, |
| and SS. The SS signal (slave select) is an active low signal that activates |
| a SPI slave device. This is how a master "addresses" a particular slave |
| device. Often this signal is also referred to as "chip select" as it |
| selects particular slave device for communications.</p> |
| <p>The Mynewt SPI HAL has blocking and non-blocking transfers. Blocking means that the API call |
| to transfer a byte will wait until the byte completes transmissions before |
| the function returns. Blocking interface can be used for only the master slave SPI type. |
| Non-blocking means he function returns control to the execution environment immediately after the API call and a callback function is executed at the completion of the transmission. Non-blocking interface can be used for both master and slave SPI types.</p> |
| <p>The <code>hal_spi_config</code> method in the API above allows the SPI to be configured with appropriate settings for master or slave. It Must be called after the spi is initialized (i.e. after hal_spi_init is called) and when the spi is disabled (i.e. user must call hal_spi_disable if the spi has been enabled through hal_spi_enable prior to calling this function). It can also be used to reconfigure an initialized SPI (assuming it is disabled as described previously).</p> |
| <div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #A90D91">int</span> <span style="color: #000000">hal_spi_config</span>(<span style="color: #A90D91">int</span> <span style="color: #000000">spi_num</span>, <span style="color: #A90D91">struct</span> <span style="color: #3F6E75">hal_spi_settings</span> <span style="color: #000000">*psettings</span>); |
| </code></pre></div> |
| |
| <p>The SPI settings consist of the following:</p> |
| <div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #A90D91">struct</span> <span style="color: #3F6E75">hal_spi_settings</span> { |
| <span style="color: #A90D91">uint8_t</span> <span style="color: #000000">data_mode</span>; |
| <span style="color: #A90D91">uint8_t</span> <span style="color: #000000">data_order</span>; |
| <span style="color: #A90D91">uint8_t</span> <span style="color: #000000">word_size</span>; |
| <span style="color: #A90D91">uint32_t</span> <span style="color: #000000">baudrate</span>; <span style="color: #177500">/* baudrate in kHz */</span> |
| }; |
| </code></pre></div> |
| |
| <p>The Mynewt SPI HAL does not include built-in SS (Slave Select) signaling. It's up to the |
| hal_spi user to control their own SS pins. Typically applications will do |
| this with GPIO.</p> |
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