Android-HAL (一) hw_module_t 的类型实现

HAL module架构主要分为三个结构体

struct hw_module_t;    //硬件抽象模块

struct hw_module_methods_t;    //方法

struct hw_device_t;    //模块中的设备

---

hardware/libhardware/include/hardware/hardware.h

1 每一个 hardware 硬件抽象模块必须有一个module结构体，名字是 HAL_MODULE_INFO_SYM，即HMI，这个模块第一个成员变量是 hw_module_t ，

2  hw_module_t 的tag的值必须为 HARDWARE_MODULE_TAG，这个值就是用来标识硬件抽象的结构体

3 id这个属性代表这个module的唯一性

4 methods代表每个硬件抽象模块的方法结构体，hw_module_methods_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;    //模块唯一id

    /** Name of this module */
    const char *name;  //id  

    /** Author/owner/implementor of the module */
    const char *author;

    /** Modules methods */
    struct hw_module_methods_t* methods;    //方法的结构体

    /** 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;

---

hw_module_methods_t 结构体

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);
    //id --设备id
    //根据id返回设备

} hw_module_methods_t;

---

hw_device_t 结构体

1 每个硬件需要定义一个 hw_device_t

2 tag为所在硬件模块HARDWARE_DEVICE_TAG，代表是硬件设备结构体

//hardware/libhardware/include/hardware/hardware.h

    #define HARDWARE_DEVICE_TAG MAKE_TAG_CONSTANT('H', 'W', 'D', 'T')

3 close指针用于关闭设备

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;

struct sensors_poll_device_t {
    struct hw_device_t common;
    int (*activate)(struct sensors_poll_device_t *dev,
            int sensor_handle, int enabled);
    int (*setDelay)(struct sensors_poll_device_t *dev,
            int sensor_handle, int64_t sampling_period_ns);
    int (*poll)(struct sensors_poll_device_t *dev,
            sensors_event_t* data, int count);
};

---

---

实现方式

定义结构体

//hardware/libhardware/include/hardware/sensors.h

#define SENSORS_HARDWARE_MODULE_ID "sensors"

struct sensors_module_t {
    struct hw_module_t common;

    // ...
};

//实现
static struct hw_module_methods_t sensors_module_methods = {
    .open = open_sensors
};

struct sensors_module_t HAL_MODULE_INFO_SYM = {
    .common = {
        .tag = HARDWARE_MODULE_TAG,
        .version_major = 1,
        .version_minor = 1,
        .id = SENSORS_HARDWARE_MODULE_ID,
        .name = "MultiHal Sensor Module",
        .author = "Google, Inc",
        .methods = &sensors_module_methods,
        .dso = NULL,
        .reserved = {0},
    },
    .get_sensors_list = module__get_sensors_list
};

static int open_sensors(const struct hw_module_t* hw_module, const char* name,
        struct hw_device_t** hw_device_out) {
    // ...
   // Create proxy device, to return later.
    sensors_poll_context_t *dev = new sensors_poll_context_t();
    memset(dev, 0, sizeof(sensors_poll_device_1_t));
    dev->proxy_device.common.tag = HARDWARE_DEVICE_TAG;
    dev->proxy_device.common.version = SENSORS_DEVICE_API_VERSION_1_4;
    dev->proxy_device.common.module = const_cast<hw_module_t*>(hw_module);
    dev->proxy_device.common.close = device__close;
    dev->proxy_device.activate = device__activate;
    dev->proxy_device.setDelay = device__setDelay;
    dev->proxy_device.poll = device__poll;
    dev->proxy_device.batch = device__batch;
    dev->proxy_device.flush = device__flush;
    dev->proxy_device.inject_sensor_data = device__inject_sensor_data;
    dev->proxy_device.register_direct_channel = device__register_direct_channel;
    dev->proxy_device.config_direct_report = device__config_direct_report;

    dev->nextReadIndex = 0;
    // ...
    return 0;
}