| Creating New HAL Interfaces |
| =========================== |
| |
| HAL API |
| ------- |
| |
| A HAL always includes header file with function declarations for the HAL |
| functionality in ``/hw/hal/include/hal``. The first argument of all |
| functions in the interface typically include the virtual device\_id of |
| the device you are controlling. |
| |
| For example, in |
| ```hal_gpio.h`` <https://github.com/apache/incubator-mynewt-core/blob/master/hw/hal/include/hal/hal_gpio.h>`__ |
| the device enumeration is the first argument to most methods and called |
| ``pin``. |
| |
| .. code-block:: console |
| |
| void hal_gpio_write(int pin, int val); |
| |
| The device\_id (in this case called ``pin``) is not a physical device |
| (actual hardware pin), but a virtual pin which is defined by the |
| implementation of the HAL (and documented in the implementation of the |
| HAL). |
