## nRFx HAL

The HAL source files provided with these models implement
some modifications to [the real nRFx HAL](https://github.com/NordicSemiconductor/nrfx/)
needed due to the HW models peculiarities.
Its main purpose is to allow unmodified embedded code to run directly
using this repository HW models.

There is two main differences in this HAL compared to the real one:

* The peripherals base addresses point to the HW models register IF
  instead of to hardcoded HW addresses.<br>
  For example `NRF_PPI_BASE` is defined as `(&NRF_PPI_regs)`, where
  `NRF_PPI_regs` is the HW models structure containing the PPI model
  registers

* When a HW register with sideeffects is written, the appropriate
  HW model function is called to trigger that sideeffect.<br>
  A sideeffect should be understood as some activity beyond the modification
  of the register itself. For example, in real HW, writting a `1` to
  `NRF_RNG->TASKS_START` will start the random number generation.
  When using the HW models, doing this write in itself would only change
  that memory location content. To trigger the actual sideeffect the
  function `nrf_rng_regw_sideeffects_TASK_START()` needs to be called.
  This replacement HAL functions take care of that.

The original implementation of the HAL APIs from the real nrfx is included in
`nrf_hal_originals.c`.
All these functions are labelled as weak, so they can be replaced as needed with content
of `src/nrfx/hal/`. This removes the need for duplicating code.

Note that this replacement HAL only provides the necessary replacements for the subset of the
nRFx API corresponding to the peripherals included in these models.
Note also that for these, not necessarily all nRFx functions which could need replacing are
included. Though those used by Zephyr should be included.
It is certainly possible to expand it to cover the whole API.