# LiteOS Cortex-A
- [Introduction](#section11660541593)
- [Directory Structure](#section161941989596)
- [Constraints](#section119744591305)
- [Usage](#section741617511812)
- [Preparations](#section1579912573329)
- [Source Code Acquisition](#section11443189655)
- [Compilation and Building](#section2081013992812)
- [Repositories Involved](#section1371113476307)
## Introduction
The OpenHarmony LiteOS Cortex-A is a new-generation kernel developed based on the Huawei LiteOS kernel. Huawei LiteOS is a lightweight operating system \(OS\) built for the Internet of Things \(IoT\) field. With the rapid development of the IoT industry, OpenHarmony LiteOS Cortex-A brings small-sized, low-power, and high-performance experience and builds a unified and open ecosystem for developers. In addition, it provides rich kernel mechanisms, more comprehensive Portable Operating System Interface \(POSIX\), and a unified driver framework, Hardware Driver Foundation \(HDF\), which offers unified access for device developers and friendly development experience for application developers. [Figure1](#fig27311582210) shows the architecture of the OpenHarmony LiteOS Cortex-A kernel.
**Figure 1** Architecture of the OpenHarmony LiteOS Cortex-A kernel
## Directory Structure
```
/kernel/liteos_a
├── apps # User-space init and shell application programs
├── arch # System architecture, such as ARM
│ └── arm # Code for ARM architecture
├── bsd # Code of the driver and adaptation layer module related to the FreeBSD, such as the USB module
├── compat # Kernel API compatibility
│ └── posix # POSIX APIs
├── drivers # Kernel driver
│ └── char # Character device
│ ├── mem # Driver for accessing physical input/output (I/O) devices
│ ├── quickstart # APIs for quick start of the system
│ ├── random # Driver for random number generators
│ └── video # Framework of the framebuffer driver
├── fs # File system module, which mainly derives from the NuttX open-source project
│ ├── fat # FAT file system
│ ├── jffs2 # JFFS2 file system
│ ├── include # Header files exposed externally
│ ├── nfs # NFS file system
│ ├── proc # proc file system
│ ├── ramfs # RAMFS file system
│ └── vfs # VFS layer
├── kernel # Kernel modules including the process, memory, and IPC modules
│ ├── base # Basic kernel modules including the scheduling and memory modules
│ ├── common # Common components used by the kernel
│ ├── extended # Extended kernel modules including the dynamic loading, vDSO, and LiteIPC modules
│ ├── include # Header files exposed externally
│ └── user # Init process loading
├── lib # Kernel library
├── net # Network module, which mainly derives from the lwIP open-source project
├── platform # Code for supporting different systems on a chip (SOCs), such as Hi3516D V300
│ ├── hw # Logic code related to clocks and interupts
│ ├── include # Header files exposed externally
│ └── uart # Logic code related to the serial port
├── platform # Code for supporting different systems on a chip (SOCs), such as Hi3516D V300
├── security # Code related to security features, including process permission management and virtual ID mapping management
├── syscall # System calling
└── tools # Building tools as well as related configuration and code
```
## Constraints
- Programming languages: C and C++
- Applicable development boards: Hi3518E V300 and Hi3516D V300
- Hi3518E V300 uses the JFFS2 file system by default, and Hi3516D V300 uses the FAT file system by default.
## Usage
OpenHarmony LiteOS Cortex-A supports the [Hi3518E V300](https://gitee.com/openharmony/docs/blob/master/docs-en/quick-start/introduction-to-the-hi3518-development-board.md) and [Hi3516D V300](https://gitee.com/openharmony/docs/blob/master/docs-en/quick-start/introduction-to-the-hi3516-development-board.md). You can develop and run your applications based on both development boards.
### Preparations
You need to set up the compilation environment on Linux.
- For Hi3518E V300, see [Setting Up the Hi3518 Development Environment](https://gitee.com/openharmony/docs/blob/master/docs-en/quick-start/setting-up-the-hi3518-development-environment.md).
- For Hi3516D V300, see [Setting Up the Hi3516 Development Environment](https://gitee.com/openharmony/docs/blob/master/docs-en/quick-start/setting-up-the-hi3516-development-environment.md).
### Source Code Acquisition
Download and decompress a set of source code on a Linux server to acquire the [source code](https://repo.huaweicloud.com/harmonyos/os/1.0/code-1.0.tar.gz). For more acquisition methods, see [Source Code Acquisition](https://gitee.com/openharmony/docs/blob/master/docs-en/get-code/source-code-acquisition.md).
### Compilation and Building
For details about how to develop the first application, see:
- [Developing the First Example Program Running on Hi3518](https://gitee.com/openharmony/docs/blob/master/docs-en/quick-start/developing-the-first-example-program-running-on-hi3518.md)
- [Developing the First Example Program Running on Hi3516](https://gitee.com/openharmony/docs/blob/master/docs-en/quick-start/developing-the-first-example-program-running-on-hi3516.md)
## Repositories Involved
[drivers\_liteos](https://gitee.com/openharmony/drivers_liteos)
**[kernel\_liteos\_a](https://gitee.com/openharmony/kernel_liteos_a)**