Detailed Description

Hardware Abstraction Layer.

Under ChibiOS the set of the various device driver interfaces is called the HAL subsystem: Hardware Abstraction Layer. The HAL is the abstract interface between ChibiOS applications and hardware.

HAL Device Drivers Architecture

The HAL contains several kind of modules:

Normal Device Drivers
Complex Device Drivers
Interfaces
Inner Code

HAL Normal Device Drivers

Normal device are meant to interface the application to the underlying hardware through an high level API. Normal Device Drivers are split in two layers:

High Level Device Driver (HLD). This layer contains the definitions of the driver's APIs and the platform independent part of the driver.
An HLD is composed by two files:
- <driver>.c, the HLD implementation file. This file must be included in the Makefile in order to use the driver.
- <driver>.h, the HLD header file. This file is implicitly included by the HAL header file hal.h.
Low Level Device Driver (LLD). This layer contains the platform dependent part of the driver.
A LLD is composed by two files:
- <driver>_lld.c, the LLD implementation file. This file must be included in the Makefile in order to use the driver.
- <driver>_lld.h, the LLD header file. This file is implicitly included by the HLD header file.

Diagram

HAL Complex Device Drivers

It is a class of device drivers that offer an high level API but do not use the hardware directly. Complex device drivers use other drivers for accessing the machine resources.

HAL Interfaces

An interface is a binary structure allowing the access to a service using virtual functions. This allows to create drivers that can be accessed using a common interface. The concept of interface is commonly found in object-oriented languages like Java or C++, their meaning in ChibiOS/HAL is exactly the same.

HAL Inner Code

Some modules are shared among multiple device drivers and are not necessarily meant to be used by the application layer.

Modules
	Configuration
	HAL Configuration.

	Normal Drivers
	HAL Normal Drivers.

	Complex Drivers
	HAL Complex Drivers.

	Interfaces and Classes
	HAL Interfaces and Classes.

	Inner Code
	HAL Inner Code.

	Support Code
	HAL Support Code.

	OSAL
	Operating System Abstraction Layer.