Android 驱动开发系列三
写blog的时候，发现跳章了，HAL硬件抽象层都没有写就到JNI了，这里补回来。
1、添加HAL头文件
进入到 android-4.0.4_r1.2/hardware/libhardware/include/hardware 目录，创建 ttt.h 文件：
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2/hardware/libhardware/include/hardware# gedit ttt.h
文件内容如下：
#ifndef ANDROID_TTT_INTERFACE_H
#define ANDROID_TTT_INTERFACE_H
#include <hardware/hardware.h>
__BEGIN_DECLS
// 定义模块ID
#define HELLO_HARDWARE_MODULE_ID "ttt"
// 硬件模块结构体
struct ttt_module_t{
struct hw_module_t common;
};
// hardware interface struct
struct ttt_device_t{
struct hw_device_t common;
int fd;
int(*set_val)(struct ttt_device_t* dev, int val);
int(*get_val)(struct ttt_device_t* dev, int* val);
};
__END_DECLS
#endif
这里按照Android硬件抽象层规范的要求，分别定义模块ID、模块结构体以及硬件接口结构体。
2、实现HAL
进入android-4.0.4_r1.2/hardware/libhardware/modules 目录，创建 ttt 目录：
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2/hardware/libhardware/modules# mkdir ttt
进入到新创建的ttt目录下面，并创建 ttt.c 文件：
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2/hardware/libhardware/modules/ttt# gedit ttt.c
其内容如下：
#define LOG_TAG "TTTStub" #include <hardware/hardware.h> #include <hardware/ttt.h> #include <fcntl.h> #include <errno.h> #include <cutils/log.h> #include <cutils/atomic.h> #define DEVICE_NAME "/dev/ttt" #define MODULE_NAME "TTT" #define MODULE_AUTHOR "[email protected]" // open/close device interface static int ttt_device_open(const struct hw_module_t* module, const char* name, struct hw_device_t** device); static int ttt_device_close(struct hw_device_t* device); // device interfaces static int ttt_set_val(struct ttt_device_t* dev, int val); static int ttt_get_val(struct ttt_device_t* dev, int* val); // module methods static struct hw_module_methods_t ttt_module_methods = { open: ttt_device_open }; // module variables const struct ttt_module_t HAL_MODULE_INFO_SYM = { common: { tag: HARDWARE_MODULE_TAG, version_major: 1, version_minor: 0, id: HELLO_HARDWARE_MODULE_ID, name: MODULE_NAME, author: MODULE_AUTHOR, methods: &ttt_module_methods, } }; // * device set value interface static int ttt_set_val(struct ttt_device_t* dev, int val) { LOGI("TTT Stub: set value %d to device.", val); write(dev->fd, &val, sizeof(val)); return 0; } // * device get value interface static int ttt_get_val(struct ttt_device_t* dev, int* val) { if(!val){ LOGE("TTT Stub: error val pointer."); return -EFAULT; } read(dev->fd, val, sizeof(*val)); LOGI("TTT Stub: get value %d from device.", *val); return 0; } // * close device interface static int ttt_device_close(struct hw_device_t* device) { struct ttt_device_t* ttt_device = (struct ttt_device_t*)device; if(ttt_device){ close(ttt_device->fd); free(ttt_device); } return 0; } // * open device interface static int ttt_device_open(const struct hw_module_t* module, const char* name, struct hw_device_t** device) { struct ttt_device_t* dev; dev = (struct ttt_device_t*)malloc( sizeof(struct ttt_device_t) ); if(!dev){ LOGE("TTT stub: failed to alloc space"); return -EFAULT; } memset(dev, 0, sizeof(struct ttt_device_t)); dev->common.tag = HARDWARE_DEVICE_TAG; dev->common.version = 0; dev->common.module = (hw_module_t*)module; dev->common.close = ttt_device_close; dev->set_val = ttt_set_val; dev->get_val = ttt_get_val; if( (dev->fd = open(DEVICE_NAME, O_RDWR)) == -1){ LOGE("TTT Stub: failed to open /dev/ttt -- %s.", strerror(errno)); free(dev); return -EFAULT; } *device = &(dev->common); LOGI("TTT Stub: open /dev/ttt successfully."); return 0; }
在该目录下创建对应的Android.mk文件：
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2/hardware/libhardware/modules/ttt# gedit Android.mk
其内容如下：
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_MODULE_TAGS := optional LOCAL_PRELINK_MODULE := false LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw LOCAL_SHARED_LIBRARIES := liblog LOCAL_SRC_FILES := ttt.c LOCAL_MODULE := ttt.default include $(BUILD_SHARED_LIBRARY)
3、添加权限
由于设备文件是在内核驱动里面通过 device_create 创建的，而 device_create 创建的设备文件默认只有 root 用户
可读写，而 ttt_device_open 一般是由上层APP来调用的，这些 APP 一般不具有 root 权限，这时候就有可能导致打开设备文件失败，提示类似于：
Permission denied.
解决办法是类似 linux 的udev 规则，
进入到 android-4.0.4_r1.2/system/core/rootdir 目录，打开 uenentd.rc 文件：
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2/system/core/rootdir# gedit ueventd.rc
在里面添加一句：
/dev/ttt 0666 root root
4、开始编译
执行命令如下：
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# mmm hardware/libhardware/modules/ttt ============================================ PLATFORM_VERSION_CODENAME=REL PLATFORM_VERSION=4.0.4 TARGET_PRODUCT=full_smdkv210 TARGET_BUILD_VARIANT=eng TARGET_BUILD_TYPE=release TARGET_BUILD_APPS= TARGET_ARCH=arm TARGET_ARCH_VARIANT=armv7-a-neon HOST_ARCH=x86 HOST_OS=linux HOST_BUILD_TYPE=release BUILD_ID=IMM76I ============================================ make:进入目录'/home/brantyou/workspace/android-4.0.4_r1.2' target thumb C: ttt.default <= hardware/libhardware/modules/ttt/ttt.c target SharedLib: ttt.default (out/target/product/smdkv210/obj/SHARED_LIBRARIES/ttt.default_intermediates/LINKED/ttt.default.so) target Symbolic: ttt.default (out/target/product/smdkv210/symbols/system/lib/hw/ttt.default.so) target Strip: ttt.default (out/target/product/smdkv210/obj/lib/ttt.default.so) Install: out/target/product/smdkv210/system/lib/hw/ttt.default.so make:离开目录“/home/brantyou/workspace/android-4.0.4_r1.2” root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2#
重新打包system.img：
root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2# make snod ============================================ PLATFORM_VERSION_CODENAME=REL PLATFORM_VERSION=4.0.4 TARGET_PRODUCT=full_smdkv210 TARGET_BUILD_VARIANT=eng TARGET_BUILD_TYPE=release TARGET_BUILD_APPS= TARGET_ARCH=arm TARGET_ARCH_VARIANT=armv7-a-neon HOST_ARCH=x86 HOST_OS=linux HOST_BUILD_TYPE=release BUILD_ID=IMM76I ============================================ build/core/Makefile:25: 警告：覆盖关于目标“out/target/product/smdkv210/system/bin/pppd”的命令 build/core/base_rules.mk:523: 警告：忽略关于目标“out/target/product/smdkv210/system/bin/pppd”的旧命令 make snod: ignoring dependencies Target system fs image: out/target/product/smdkv210/system.img out/target/product/smdkv210/system.img total size is 150853824 root@brantyou-ubuntu:~/workspace/android-4.0.4_r1.2#
到此，HAL层的就编写完了，下一篇就是编写对应的JNI接口了。