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<h1 id="hal_gpio">hal_gpio</h1>
<p>This is the hardware independent GPIO (General Purpose Input Output) Interface for Mynewt.</p>
<h3 id="description">Description</h3>
<p>Contains the basic operations to set and read General Purpose Digital I/O Pins
within a Mynewt system.</p>
<p>Individual GPIOs are referenced in the APIs as <code>pins</code>. However, in this interface the <code>pins</code> are virtual GPIO pins. The MCU header file maps these virtual <code>pins</code> to the physical GPIO ports and pins.</p>
<p>Typically, the BSP code may define named I/O pins in terms of these virtual <code>pins</code> to describe the devices attached to the physical pins.</p>
<p>Here's a brief example so you can get the gist of the translation.</p>
<p>Suppose my product uses the stm32F4xx processor. There already exists support for this processor within Mynewt. The processor has N ports (A,B,C..) of 16 GPIO pins per port. The MCU hal_gpio driver maps these to a set of virtual pins 0-N where port A maps to 0-15, Port B maps to 16-31, Port C maps to 32-47 and so on. The exact number of physical port (and virtual
port pins) depends on the specific variant of the stm32F4xx. </p>
<p>So if I want to turn on port B pin 3, that would be virtual pin 1*16 + 3 = 19.
This translation is defined in the MCU implementation of
<a href="https://github.com/apache/incubator-mynewt-core/blob/master/hw/mcu/stm/stm32f4xx/src/hal_gpio.c">hal_gpio.c</a>
for the stmf32F4xx. Each MCU will typically have a different translation method
depending on its GPIO architecture.</p>
<p>Now, when writing a BSP, it's common to give names to the relevant port pins that you are using. Thus, the BSP may define a mapping between a function and a virtual port pin in the <code>bsp.h</code> header file for the BSP. For example,</p>
<div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code>#define SYSTEM_LED (37)
#define FLASH_SPI_CHIP_SELECT (3)
</code></pre></div>
<p>would map the system indicator LED to virtual pin 37 which on the stm32F4xx would be Port C pin 5 and the chip select line for the external SPI flash to virtual pin 3 which on the stm32F4xxis port A pin 3.</p>
<p>Said another way, in this specific system we get</p>
<div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code>SYSTEM_LED --&gt; hal_gpio virtual pin 37 --&gt; port C pin 5 on the stm34F4xx
</code></pre></div>
<h3 id="definition">Definition</h3>
<p><a href="https://github.com/apache/incubator-mynewt-core/blob/master/hw/hal/include/hal/hal_gpio.h">hal_gpio.h</a></p>
<h3 id="examples">Examples</h3>
<h4 id="blinky">Blinky</h4>
<p>Blinky uses the hal_gpio to blink the system LED. The blinky source code is available in the
<a href="https://github.com/apache/incubator-mynewt-blinky/blob/master/apps/blinky/src/main.c">blinky repo</a>.
Examine how <code>blinky_task_handler</code> initializes and toggles the GPIO to control the LED.</p>
<p><br></p>
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