# LiteOS Cortex-A ## Overview ### Porting Scenario LiteOS Cortex-A supports the ARMv7-a instruction set architecture. If you are porting the kernel to a chipset that uses ARMv7-a, you can directly perform basic adaptation. Otherwise, you need to add support for the architecture used by the chipset. This process is complex and not covered in this document. ### Directory Specifications For details about the LiteOS Cortex-A directory specifications, see [LiteOS Cortex-A Overview](https://gitee.com/openharmony/kernel_liteos_a). ## Adaptation Process LiteOS Cortex-A provides the system initialization process and custom configuration options required for system running. During porting, pay attention to the functions related to hardware configuration in the initialization process. The LiteOS Cortex-A initialization process consists of seven steps: 1. Add the **target\_config.h** file and compile the macros **DDR\_MEM\_ADDR** and **DDR\_MEM\_SIZE**, which indicate the start address and length of the board memory, respectively. The prelinker script **board.ld.S** creates the linker script **board.ld** based on the two macros. 2. Define **g\_archMmuInitMapping**, the global array of MMU mappings, to specify the memory segment attributes and the virtual-to-physical address mappings. The memory mapping will be established based on this array during kernel startup. 3. If there are multiple cores, define **struct SmpOps**, the handle to the slave core operation function. The **SmpOps-\>SmpCpuOn** function needs to implement the feature of waking up a slave core. Then, define the **SmpRegFunc** function and call the **LOS\_SmpOpsSet** interface to register the handle. The registration process is completed by starting the framework using **LOS\_MODULE\_INIT\(SmpRegFunc, LOS\_INIT\_LEVEL\_EARLIEST\)**. 4. Create a kernel image based on the linker script **board.ld**. 5. Perform operations such as initialization of the interrupt vector table and MMU page table are performed in the assembly files: **reset\_vector\_up.S** and **reset\_vector\_mp.S**, from which a single-core CPU and a multi-core CPU start, respectively. 6. Enable the assembly code in **reset\_vector.S** to jump to the **main** function of the C programming language to initialize the hardware clock, software timer, memory, and tasks. This process depends on the feature macro configuration in **target\_config.h**. Then, create the **SystemInit** task to be implemented in the board code, with **OsSchedStart\(\)** enabled for task scheduling. 7. Call the **DeviceManagerStart** function to initialize the HDF driver. This process is implemented by calling the driver configuration file **hdf.hcs** and drivers source code in the board code. The figure below shows the overall initialization process. **Figure 1** Overall initialization process ![](figures/overall-initialization-process.png "overall-initialization-process") As can be seen from preceding figure, kernel basic adaptation involves the following parts: - Adding the **target\_config.h** file, which contains board hardware parameters and feature parameters described in the following table: **Table 1** Parameters in the target\_config.h file

Parameter	Description
OS_SYS_CLOCK	System cycle frequency
DDR_MEM_ADDR	Start address of the system memory
DDR_MEM_SIZE	Size of the system memory
PERIPH_PMM_BASE	Base address of the peripheral register
PERIPH_PMM_SIZE	Size of the peripheral register
OS_HWI_MIN	Minimum number of system interrupts
OS_HWI_MAX	Maximum number of system interrupts
NUM_HAL_INTERRUPT_UART0	UART0 interrupt ID
UART0_REG_BASE	UART0 register base address
GIC_BASE_ADDR	Base address of the GIC interrupt register
GICD_OFFSET	Offset address of the GICD relative to the GIC base address
GICC_OFFSET	Offset address of the GICC relative to the GIC base address

- Implementing the **SystemInit** function to initialize services in the user space. Figure 2 shows a typical initialization scenario. **Figure 2** Service startup process ![](figures/service-startup-process.png "service-startup-process") - Implementing the **main** function for basic kernel initialization and initialization of services in the board kernel space. [Figure 3](#fig32611728133919) shows the initialization process, where the kernel startup framework takes the lead in the initialization process. The light blue part in the figure indicates the phase in which external modules can be registered and started in the startup framework. >![](../public_sys-resources/icon-caution.gif) **CAUTION:** >Modules at the same layer cannot depend on each other. **Figure 3** Kernel startup framework ![](figures/kernel-startup-framework.jpg "kernel-startup-framework") **Table 2** Startup framework layers

Layer	Description
LOS_INIT_LEVEL_EARLIEST	Earliest initialization. This layer does not depend on the architecture. The board and subsequent modules, such as the Trace module, will initialize the software-only modules on which they depend.
LOS_INIT_LEVEL_ARCH_EARLY	Early initialization of the architecture. This layer depends on the architecture. Subsequent modules will initialize the modules on which they depend. It is recommended that functions not required for startup be placed at the LOS_INIT_LEVEL_ARCH layer.
LOS_INIT_LEVEL_PLATFORM_EARLY	Early initialization of the platform. This layer depends on the board platform and drivers. Subsequent modules will initialize the modules on which they depend. It is recommended that functions required for startup be placed at the LOS_INIT_LEVEL_PLATFORM layer. Example: UART module
LOS_INIT_LEVEL_KMOD_PREVM	Kernel module initialization before memory initialization. This layer involves initialization of the modules that need to be enabled before memory initialization.
LOS_INIT_LEVEL_VM_COMPLETE	Initialization after the basic memory is ready. This layer involves initialization of the modules that need to be enabled and do not depend on the inter-process communication mechanism and system processes. Example: shared memory function
LOS_INIT_LEVEL_ARCH	Late initialization of the architecture. This layer depends on the architecture extension function. Subsequent modules will initialize the modules on which they depend.
LOS_INIT_LEVEL_PLATFORM	Late initialization of the platform. This layer depends on the board platform and drivers. Subsequent modules will initialize the modules on which they depend. Example: initialization of the driver kernel abstraction layer (MMC and MTD)
LOS_INIT_LEVEL_KMOD_BASIC	Initialization of the kernel basic modules. This layer is used to initialize the basic modules that can be detached from the kernel. Example: VFS initialization
LOS_INIT_LEVEL_KMOD_EXTENDED	Initialization of the kernel extended modules. This layer is used to initialize the extended modules that can be detached from the kernel. Example: system call initialization, ProcFS initialization, Futex initialization, HiLog initialization, HiEvent initialization, and LiteIPC initialization
LOS_INIT_LEVEL_KMOD_TASK	Kernel task creation. This layer can be used to create kernel tasks (kernel thread and software timer tasks). Example: creation of the resident resource reclaiming task, SystemInit task, and CPU usage statistics task

Adaptation for board porting. Focus on layers between **LOS\_INIT\_LEVEL\_ARCH** and **LOS\_INIT\_LEVEL\_KMOD\_TASK** and try to divide the initialization process into as many phases as possible for refined registration. >![](../public_sys-resources/icon-note.gif) **NOTE:** >Modules at the same layer cannot depend on each other. It is recommended that a new module be split based on the preceding startup phase and be registered and started as required. >You can view the symbol table in the **.rodata.init.kernel.\*** segment of the **OHOS\_Image.map** file generated after the build is complete, so as to learn about the initialization entry of each module that has been registered with the kernel startup framework and check whether the newly registered initialization entry takes effect. ### Programming Example In the board SDK file: ``` /* Header file of the kernel startup framework */ #include "los_init.h" ...... /* Initialization function of the new module */ unsigned int OsSampleModInit(void) { PRINTK("OsSampleModInit SUCCESS!\n"); ...... } ...... /* Register the new module at the target layer of the startup framework. */ LOS_MODULE_INIT(OsSampleModInit, LOS_INIT_LEVEL_KMOD_EXTENDED); ``` ## Verification ``` main core booting up... OsSampleModInit SUCCESS! releasing 1 secondary cores cpu 1 entering scheduler cpu 0 entering scheduler ``` According to the preceding information displayed during the system startup, the kernel calls the initialization function of the registered module during the startup to initialize the module. The system enters the kernel-space shell and the task commands can be properly executed. ``` OHOS # help *******************shell commands:************************* arp cat cd chgrp chmod chown cp cpup date dhclient dmesg dns format free help hwi ifconfig ipdebug kill log ls lsfd memcheck mkdir mount netstat oom partinfo partition ping ping6 pmm pwd reset rm rmdir sem shm stack statfs su swtmr sync systeminfo task telnet touch umount uname v2p virstatfs vmm watch writeproc ```