硬件访问服务AIDL HAL

JNI 向上提供本地函数, 向下加载HAL文件并调用HAL的函数
HAL 负责访问驱动程序执行硬件操作

在Android 5 中 HAL module 框架主要分为如下三个结构体

hardware/libhardware/include/hardware/hardware.h 文件中定义

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.
 * 大概的意思是 
硬件层必须导出  HAL_MODULE_INFO_SYM 且 一个成员变量必须是 hw_module_t
 */
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;

#ifdef __LP64__
    uint64_t reserved[32-7];
#else
    /** padding to 128 bytes, reserved for future use */
    uint32_t reserved[32-7];
#endif

} hw_module_t;

说明：1.硬件抽象层必须自定义一个硬件模块结构体且第一个成员变量必须是 hw_module_t

　　　2.必须存在一个导出符号HAL_MODULE_INFO_SYM

　 3.tag成员值必须设置为HARDWARE_MODULE_TAG

4.methods定义了硬件抽象层模块的操作方法列表类型是 hw_module_methods_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;

说明：module 硬件所在模块

id设备Id

device 打开的设备

/**
 * 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 */
#ifdef __LP64__
    uint64_t reserved[12];
#else
    uint32_t reserved[12];
#endif

    /** Close this device */
    int (*close)(struct hw_device_t* device);

} hw_device_t;

说明：1.每一个硬件设备必须自定义一个设备结构体且第一个成员变量必须是hw_device_t

2.结构体hw_device_t 成员tag必须设置值为HARDWARE_DEVICE_TAG

3.成员close 是一个函数指针用来关闭一个硬件设备

调用梗概：

　　1. 模块名==>文件名

　　　　hw_get_module_by_class("led", NULL)
　　　　name = "led"
　　　　property_get xxx是某个属性
　　　　hw_module_exists 判断是否存在led.xxx.so

　　2. 加载
　　　　dlopen(filename)
　　　　dlsym("HMI") 从SO文件中获得名为HMI的hw_module_t结构体
　　　　strcmp(id, hmi->id) 判断名字是否一致(hmi->id, "led")

hw_module_exists(char *path, size_t path_len, const char *name,const char *subname)

　　它用来判断"name"."subname".so文件是否存在
　　查找的目录：
　　　　a. HAL_LIBRARY_PATH 环境变量
　　　　b. /vendor/lib/hw
　　　　c. /system/lib/hw

JNI 怎么使用HAL

　　a. hw_get_module 获得一个hw_module_t结构体

　　b. 调用 module->methods->open(module, device_name, &device)
　　　获得一个hw_device_t结构体
　　　并且把hw_device_t结构体转换为设备自定义的结构体

struct led_device_t{
    struct hw_device_t common;
    int (*led_open)(struct led_device_t* dev);
    int (*led_ctrl)(struct led_device_t * dev,int which,int status);
};

HAL 怎么编写

　　a. 实现一个名为HMI的hw_module_t结构体
　　b. 实现一个open函数, 它会根据name返回一个设备自定义的结构体
　　　这个设备自定义的结构体的第1个成员是 hw_device_t结构体
　　　还可以定义设备相关的成员

dlopen()

posted @ 2016-02-14 16:06 清渡茶叶阅读(780) 评论(0) 编辑收藏举报

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硬件访问服务AIDL HAL

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