标签:
很重要的一点,android代码是运行在linux应用层的,包括HAL层的代码。
HAL的三个结构体:hw_module_t, hw_module_methods_t, hw_device_t。
hardware\libhardware\include\hardware\Hardware.h:
struct hw_module_t; struct hw_module_methods_t; struct hw_device_t; /** * Every hardware module must have a data structure named HAL_MODULE_INFO_SYM * and the fields of this data structure must begin with hw_module_t * followed by module specific information. */ typedef struct hw_module_t { /** tag must be initialized to HARDWARE_MODULE_TAG */ uint32_t tag; /** * The API version of the implemented module. The module owner is * responsible for updating the version when a module interface has * changed. * * The derived modules such as gralloc and audio own and manage this field. * The module user must interpret the version field to decide whether or * not to inter-operate with the supplied module implementation. * For example, SurfaceFlinger is responsible for making sure that * it knows how to manage different versions of the gralloc-module API, * and AudioFlinger must know how to do the same for audio-module API. * * The module API version should include a major and a minor component. * For example, version 1.0 could be represented as 0x0100. This format * implies that versions 0x0100-0x01ff are all API-compatible. * * In the future, libhardware will expose a hw_get_module_version() * (or equivalent) function that will take minimum/maximum supported * versions as arguments and would be able to reject modules with * versions outside of the supplied range. */ uint16_t module_api_version; #define version_major module_api_version /** * version_major/version_minor defines are supplied here for temporary * source code compatibility. They will be removed in the next version. * ALL clients must convert to the new version format. */ /** * The API version of the HAL module interface. This is meant to * version the hw_module_t, hw_module_methods_t, and hw_device_t * structures and definitions. * * The HAL interface owns this field. Module users/implementations * must NOT rely on this value for version information. * * Presently, 0 is the only valid value. */ uint16_t hal_api_version; #define version_minor hal_api_version /** Identifier of module */ const char *id; /** Name of this module */ const char *name; /** Author/owner/implementor of the module */ const char *author; /** Modules methods */ struct hw_module_methods_t* methods; /** module‘s dso */ void* dso; /** padding to 128 bytes, reserved for future use */ uint32_t reserved[32-7]; } hw_module_t; typedef struct hw_module_methods_t { /** Open a specific device */ int (*open)(const struct hw_module_t* module, const char* id, struct hw_device_t** device); } hw_module_methods_t; /** * Every device data structure must begin with hw_device_t * followed by module specific public methods and attributes. */ typedef struct hw_device_t { /** tag must be initialized to HARDWARE_DEVICE_TAG */ uint32_t tag; /** * Version of the module-specific device API. This value is used by * the derived-module user to manage different device implementations. * * The module user is responsible for checking the module_api_version * and device version fields to ensure that the user is capable of * communicating with the specific module implementation. * * One module can support multiple devices with different versions. This * can be useful when a device interface changes in an incompatible way * but it is still necessary to support older implementations at the same * time. One such example is the Camera 2.0 API. * * This field is interpreted by the module user and is ignored by the * HAL interface itself. */ uint32_t version; /** reference to the module this device belongs to */ struct hw_module_t* module; /** padding reserved for future use */ uint32_t reserved[12]; /** Close this device */ int (*close)(struct hw_device_t* device); } hw_device_t;
HAL源文件中要定义一个结构体hw_module_t, 它里面包含了hw_module_methods_t。
hw_module_methods_t只有一个成员函数open:
int (*open)(const struct hw_module_t* module, const char* id,
struct hw_device_t** device);
在函数内部,需要返回一个hw_device_t结构体。
或者定义扩展的hw_device_t,例如:
struct xxx_device_t { struct hw_device_t common; //以下成员是HAL对上层提供的接口或一些属性 int fd; int (*set_val)(struct xxx_device_t* dev, int val); int (*get_val)(struct xxx_device_t* dev, int* val); };
定义结构体时,变量名必须为HAL_MODULE_INFO_SYM,例如:
/*模块实例变量*/ struct xxx_module_t HAL_MODULE_INFO_SYM = { common: { tag: HARDWARE_MODULE_TAG, version_major: 1, version_minor: 0, id: XXX_HARDWARE_MODULE_ID, //头文件中有定义 name: MODULE_NAME, author: MODULE_AUTHOR, methods: &xxx_module_methods, } };
版权声明:本文为博主原创文章,未经博主允许不得转载。
标签:
原文地址:http://blog.csdn.net/xgbing/article/details/48140471