實作自己的HAL2 HAL helloworld 之HAL層代碼的撰寫

撰寫目標

• 撰寫一個實作簡單功能（加法運算）的HAL代碼，不涉及驅動操作
• 編譯通過并打包到system.ing中

撰寫頭檔案helloworld.h

#define ANDROID_HELLOWORLD_INTERFACE_H
#include <hardware/hardware.h>

__BEGIN_DECLS

//定義模塊ID
#define HELLOWORLD_HARDWARE_MODULE_ID "helloworld"

//硬體模塊結構

struct helloworld_module_t
{
    struct hw_module_t common;
    char * description;
    int methodsNum;
};

//硬體介面結構體

struct helloworld_device_t
{
    struct  hw_device_t common;
    int (*helloworld_add) (struct helloworld_device_t *dev, int a , int b, int *c);
};


__END_DECLS

撰寫helloworld.c

• 在系統原始碼的這個路徑 Z:\itop-3399_8.1\hardware\libhardware\modules ，下新建helloworld 檔案夾
• 在helloworld檔案夾下創建helloworld.c檔案
  代碼

#define LOG_TAG "HelloStub"

#include <hardware/hardware.h>
#include <malloc.h>
#include <fcntl.h>
#include <errno.h>
#include <cutils/log.h>
#include <hardware/helloworld.h>

#define MODULE_NAME "helloworld"
#define MODULE_DES "HelloWorld : Implement Add function"
#define MODULE_AUTHOR "963416867@qq.com"

static int helloworld_open(const struct hw_module_t* module, const char* id, struct hw_device_t** device);
static int helloworld_close(struct hw_device_t* device);
static int helloworld_add(struct helloworld_device_t *dev, int a , int b, int *c);
static int  helloworld_open(const struct hw_module_t* module, const char* id, struct hw_device_t** device){

    __android_log_print(ANDROID_LOG_INFO, LOG_TAG, "helloworld_open");


    struct helloworld_device_t *dev;
    
    dev = (struct helloworld_device_t *)malloc(sizeof(struct helloworld_device_t));
    if(!dev){
        ALOGE("Helloworld open: faild to alloc device space");
        return -EFAULT;
    }

    memset(dev, 0, sizeof(struct helloworld_device_t));
    dev->common.tag = HARDWARE_MODULE_TAG;
    dev->common.version = 0;
    dev->common.module = (hw_module_t *)module;
    dev->common.close = helloworld_close;
    dev->helloworld_add = helloworld_add;
    * device = &(dev->common);
    ALOGE("helloworld open: driver file successfully");
   

    return 0;
    }

static struct  hw_module_methods_t helloworld_module_methods_t = {
    .open = helloworld_open
};

//module struct  注意這里必須是 HAL_MODULE_INFO_SYM 變數名

struct helloworld_module_t HAL_MODULE_INFO_SYM = {

    .common = {
        .tag = HARDWARE_MODULE_TAG,
        .module_api_version = 1,
        .hal_api_version = 0,
        .id = HELLOWORLD_HARDWARE_MODULE_ID,
        .name = MODULE_NAME,
        .author = MODULE_AUTHOR,
        .methods = &helloworld_module_methods_t
    },

    .description = MODULE_DES,
    .methodsNum = 3

};

static int helloworld_close(struct hw_device_t* device){
    struct helloworld_device_t* helloworld_device= (struct helloworld_device_t *)device;
    if(helloworld_device){
        free(helloworld_device);
    }

    return 0;
}

static int helloworld_add(struct helloworld_device_t *dev, int a , int b, int *c){
    ALOGI("helloworld add: success %d + %d", a, b);
    *c = a + b;
    return 0;
}

撰寫Android.mk 編譯檔案

• Android.mk

# Copyright (C) 2008 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


LOCAL_PATH := $(call my-dir)

# HAL module implemenation stored in
# hw/<OVERLAY_HARDWARE_MODULE_ID>.<ro.product.board>.so
include $(CLEAR_VARS)

#用于列印的庫
LOCAL_LDLIBS := -llog

LOCAL_MODULE_RELATIVE_PATH := hw
LOCAL_PROPRIETARY_MODULE := true
LOCAL_SRC_FILES := helloworld.c
LOCAL_HEADER_LIBRARIES := libhardware_headers
LOCAL_MODULE := helloworld.default
LOCAL_CFLAGS:= -DLOG_TAG=\"helloworld\"
LOCAL_MODULE_TAGS := optional
include $(BUILD_SHARED_LIBRARY)

編譯自己寫的helloworld hal

• 在編譯這個模塊前先將系統原始碼編譯通過，為編譯系統原始碼會生成好多工具，這些工具可以用來單獨模塊編譯
• 配置執行檔案

source build//envsetup.sh

• 選擇在什么環境編譯

lunch

• 編譯自己撰寫的模塊

mmm hardware/libhardware/modules/helloworld/

• 打包system.img 鏡像

make snod