第1课第4.4节_Android硬件访问服务编写HAL代码

Posted 2020-09-22

4 编写HAL代码

源码下载方法
第一次:
git clone https://github.com/weidongshan/SYS_0001_LEDDemo.git
更新:
git pull origin
取出指定版本:
git checkout v1 // 有JNI没有HAL
git checkout v2 // 有JNI,HAL
git checkout v3 // add MODULE TAG, DEVICE TAG

 

 

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

dlopen

external\\chromium_org\\third_party\\hwcplus\\src\\hardware.c   (参考代码)
hw_get_module("led")

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

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

 

 

 

 /vendor/lib/hw 这个目录下没有文件，tiny4412所以只能去/system/lib/hw这个目录下找

 

 

 

2. 加载
load
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")

 

V2:
(3) JNI: 重新上传
frameworks/base/services/core/jni/com_android_server_LedService.cpp

(4) HAL: led_hal.h
led_hal.c
把新文件上传到服务器, 所在目录:
hardware/libhardware/include/hardware/led_hal.h

 

hardware/libhardware/modules 在这个目录下创建一个目录led,放入led_hal.c和自己写一个Android.mk

hardware/libhardware/modules/led/led_hal.c
hardware/libhardware/modules/led/Android.mk

Android.mk内容如下:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := led.default
LOCAL_MODULE_RELATIVE_PATH := hw
LOCAL_C_INCLUDES := hardware/libhardware
LOCAL_SRC_FILES := led_hal.c
LOCAL_SHARED_LIBRARIES := liblog
LOCAL_MODULE_TAGS := eng

include $(BUILD_SHARED_LIBRARY)

编译：

$ mmm frameworks/base/services
$ mmm hardware/libhardware/modules/led
$ make snod
$ ./gen-img.sh

 

最终生成system.img文件

打印信息简介：
a. 有三类打印信息: app, system, radio
程序里使用 ALOGx, SLOGx, RLOGx来打印
b. x表示6种打印级别，有:
V    Verbose
D    Debug
I     Info
W   Warn
E    Error
F    Fatal

比如:
#define LOG_TAG "LedHal"
ALOGI("led_open : %d", fd);

c. 打印出来的格式为:
I/LedHal ( 1987): led_open : 65
(级别) LOG_TAG 进程号 打印信息

d. 使用 logcat 命令查看
logcat LedHal:I *:S

选出自己感兴趣的信息：

 

和上一个章节相比，主要修改了

com_android_server_LedService.cpp

添加了led_hal.h   led_hal.c  Android.mk

 

 com_android_server_LedService.cpp

#define LOG_TAG "LedService"

#include "jni.h"
#include "JNIHelp.h"
#include "android_runtime/AndroidRuntime.h"

#include <utils/misc.h>
#include <utils/Log.h>

#include <stdio.h>

#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <hardware/led_hal.h>


namespace android
{

static led_device_t* led_device;

jint ledOpen(JNIEnv *env, jobject cls)
{
    jint err;
    hw_module_t* module;
    hw_device_t* device;

    ALOGI("native ledOpen ...");

    /* 1. hw_get_module */
    err = hw_get_module("led", (hw_module_t const**)&module);
    if (err == 0) {
        /* 2. get device : module->methods->open */
        err = module->methods->open(module, NULL, &device);
        if (err == 0) {
            /* 3. call led_open */
            led_device = (led_device_t *)device;
            return led_device->led_open(led_device);
        } else {
            return -1;
        }
    }
    
    return -1;    
}

void ledClose(JNIEnv *env, jobject cls)
{
    //ALOGI("native ledClose ...");
    //close(fd);
}


jint ledCtrl(JNIEnv *env, jobject cls, jint which, jint status)
{
    ALOGI("native ledCtrl %d, %d", which, status);
    return led_device->led_ctrl(led_device, which, status);
}


static const JNINativeMethod methods[] = {
    {"native_ledOpen", "()I", (void *)ledOpen},
    {"native_ledClose", "()V", (void *)ledClose},
    {"native_ledCtrl", "(II)I", (void *)ledCtrl},
};
    

int register_android_server_LedService(JNIEnv *env)
{
    return jniRegisterNativeMethods(env, "com/android/server/LedService",
            methods, NELEM(methods));
}

}

 

led_hal.c

#define LOG_TAG "LedHal"


/* 1. 实现一个名为HMI的hw_module_t结构体 */

/* 2. 实现一个open函数, 它返回led_device_t结构体 */

/* 3. 实现led_device_t结构体 */

/* 参考 hardware\\libhardware\\modules\\vibrator\\vibrator.c
 */

#include <hardware/vibrator.h>
#include <hardware/hardware.h>

#include <cutils/log.h>

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>

#include <hardware/led_hal.h>

#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <utils/Log.h>


static int fd;


/** Close this device */
static int led_close(struct hw_device_t* device)
{
    close(fd);
    return 0;
}

static int led_open(struct led_device_t* dev)
{
    fd = open("/dev/leds", O_RDWR);
    ALOGI("led_open : %d", fd);
    if (fd >= 0)
        return 0;
    else
        return -1;
}

static int led_ctrl(struct led_device_t* dev, int which, int status)
{
    int ret = ioctl(fd, status, which);
    ALOGI("led_ctrl : %d, %d, %d", which, status, ret);
    return ret;
}




static struct led_device_t led_dev = {
    .common = {
        .tag   = HARDWARE_DEVICE_TAG,
        .close = led_close,
    },
    .led_open  = led_open,
    .led_ctrl  = led_ctrl,
};

static int led_device_open(const struct hw_module_t* module, const char* id,
        struct hw_device_t** device)
{
    *device = &led_dev;
    return 0;
}


static struct hw_module_methods_t led_module_methods = {
    .open = led_device_open,
};

struct hw_module_t HAL_MODULE_INFO_SYM = {
    .tag = HARDWARE_MODULE_TAG,
    .id = "led",
    .methods = &led_module_methods,
};

 

led_hal.h

#ifndef ANDROID_LED_INTERFACE_H
#define ANDROID_LED_INTERFACE_H

#include <stdint.h>
#include <sys/cdefs.h>
#include <sys/types.h>

#include <hardware/hardware.h>

__BEGIN_DECLS

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);
};


__END_DECLS

#endif  // ANDROID_LED_INTERFACE_H