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2012-08-07 14:56 2608人阅读 举报
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android开发(5)
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在android开发和移植过程中,有时需要对某设备进行读写,但系统可能并未提供相应的服务。我们就需要自己开发硬件访问服务来控制设备。下面的例子是读写最简单的i2c设备eeprom的流程, i2c的驱动编写有两种方式,一种是利用系统提供的i2c-dev.c来实现一个i2c适配器的设备文件,然后通过在应用层操作I2C适配器来控制I2C设备;另一种是为I2C从设备独立编写一个设备驱动,不需要i2c-dev.c文件。由于前者比较简单通用性强,我们采用前者来展开。
根据android层次划分,我们照例对开发分为如下几步:
1. 添加HAL层接口模块访问设备
2. 使用JNI在应用程序框架层添加服务访问接口
3. 使用服务接口api开发应用程序
一. 添加HAL层接口模块访问设备
首先确认物理设备正常。根据开发板说明书获知设备挂载在/dev/i2c-1上,检测到该设备的存在,则通用设备驱动正常。
eeprom设备为at24c**系列,根据说明书获知设备从地址为0x50,准备工作完毕。
1. 编写hal层接口模块头文件iic.h
进入源码根目录下hardware/libhardware/include/hardware目录新建iic.h,代码如下:
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#ifndef ANDROID_IIC_INTERFACE_H
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#define ANDROID_IIC_INTERFACE_H
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#include
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__BEGIN_DECLS
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#define IIC_HARDWARE_MODULE_ID "iic"
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struct iic_module_t {
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struct hw_module_t common;
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};
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struct iic_device_t {
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struct hw_device_t common;
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int fd;
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int (*iic_write)(struct iic_device_t* dev, unsigned char* dataBuf, unsigned short slaveAddr, unsigned short subAddr, int len);
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int (*iic_read)(struct iic_device_t* dev, unsigned char* dataBuf, unsigned short slaveAddr, int len);
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};
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__END_DECLS
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#endif
这里定义了iic_write和iic_read两个接口,头文件按照hal规范编写。
2. 编写hal层接口模块文件
进入源码根目录下hardware/libhardware/modules目录新建iic目录,并在iic目录中添加iic.c,代码如下:
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#include
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#include
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#include
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#include
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#include
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#include
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#include
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#include
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#include
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#include
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#include
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#include
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#include
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#include
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#include
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"font-size:14px;">#define DEVICE_NAME "/dev/i2c-1"
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#define MODULE_NAME "iic"
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#define MODULE_AUTHOR "mfayz@sohu.com"
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#define I2C_RETRIES 0x0701/* number of times a device address should be polled when not acknowledging */
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#define I2C_TIMEOUT 0x0702/* set timeout in units of 10 ms */
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#define I2C_RDWR 0x0707
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struct i2c_msg
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{
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unsigned short addr;
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unsigned short flags;
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#define I2C_M_TEN 0x0010
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#define I2C_M_RD 0x0001
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unsigned short len;
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unsigned char *buf;
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};
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struct i2c_rdwr_ioctl_data {
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struct i2c_msg *msgs;
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int nmsgs;
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};
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static int iic_device_open(const struct hw_module_t* module, const char* name, struct hw_device_t** device);
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static int iic_device_close(struct hw_device_t* device);
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static int iic_write(struct iic_device_t* dev, unsigned char* dataBuf, unsigned short slaveAddr, unsigned short subAddr, int len);
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static int iic_read(struct iic_device_t* dev, unsigned char* dataBuf, unsigned short slaveAddr, int len);
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static struct hw_module_methods_t iic_module_methods = {
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open: iic_device_open
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};
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struct i2c_rdwr_ioctl_data iic_data;
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int ret;
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struct iic_module_t HAL_MODULE_INFO_SYM = {
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common: {
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tag: HARDWARE_MODULE_TAG,
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version_major: 1,
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version_minor: 0,
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id: IIC_HARDWARE_MODULE_ID,
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name: MODULE_NAME,
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author: MODULE_AUTHOR,
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methods: &iic_module_methods,
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}
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};
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static int iic_device_open(const struct hw_module_t* module, const char* name, struct hw_device_t** device){
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struct iic_device_t* dev;
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dev = (struct iic_device_t*)malloc(sizeof(struct iic_device_t));
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if(!dev) {
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LOGE("iic Stub: failed to alloc space");
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return -EFAULT;
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}else{
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LOGE("hal: alloc space succ!");
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}
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memset(dev, 0, sizeof(struct iic_device_t));
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dev->common.tag = HARDWARE_DEVICE_TAG;
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dev->common.version = 0;
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dev->common.module = (hw_module_t*)module;
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dev->common.close = iic_device_close;
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dev->iic_write = iic_write;
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dev->iic_read = iic_read;
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*device = &dev->common;
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if((dev->fd = open(DEVICE_NAME, O_RDWR)) == -1) {
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LOGE("iic Stub hal: failed to open /dev/i2c-1 -- %s.", strerror(errno));
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free(dev);
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return -EFAULT;
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}else{
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LOGI("iic Stub hal: open /dev/i2c-1 successfully.");
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iic_data.nmsgs=2;
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iic_data.msgs=(struct i2c_msg*)malloc(iic_data.nmsgs*sizeof(struct i2c_msg));
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if(!iic_data.msgs){
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LOGE("malloc error");
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close(dev->fd);
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exit(1);
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}
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ioctl(dev->fd, I2C_TIMEOUT, 2);
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ioctl(dev->fd, I2C_RETRIES, 1);
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}
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return 0;
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}
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static int iic_device_close(struct hw_device_t* device) {
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struct iic_device_t* iic_device = (struct iic_device_t*)device;
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if(iic_device) {
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close(iic_device->fd);
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free(iic_device);
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}
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return 0;
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}
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static int iic_write(struct iic_device_t* dev, unsigned char* dataBuf, unsigned short slaveAddr, unsigned short subAddr, int len) {
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int count = 0;
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unsigned char data[2];
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unsigned char bytes;
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LOGI("iic Stub hal: set value %s to device.", dataBuf);
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iic_data.nmsgs=1;
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(iic_data.msgs[0]).len=2;
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(iic_data.msgs[0]).addr=slaveAddr;
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(iic_data.msgs[0]).flags=0;
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(iic_data.msgs[0]).buf=(unsigned char*)malloc(2);
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while(count
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bytes = 0;
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data[bytes++] = subAddr;
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data[bytes] = dataBuf[count];
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LOGI("IIC write HAL: %x,%x", data[0],data[1]);
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(iic_data.msgs[0]).buf=data;
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ret=ioctl(dev->fd,I2C_RDWR,(unsigned long)&iic_data);
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if(ret<0){
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LOGI("IIC HAL ioctl error");
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}
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count++;
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subAddr++;
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usleep(3000);
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}
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LOGI("you have write %s into iic at %x address len: %d",dataBuf, subAddr, len);
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return 0;
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}
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static int iic_read(struct iic_device_t* dev, unsigned char* dataBuf, unsigned short slaveAddr, int len){
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int count = 0;
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iic_data.nmsgs=1;
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(iic_data.msgs[0]).len=1;
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(iic_data.msgs[0]).addr=slaveAddr;
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(iic_data.msgs[0]).flags=I2C_M_RD;
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(iic_data.msgs[0]).buf=(unsigned char*)malloc(1);
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while(count
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(iic_data.msgs[0]).buf= dataBuf++;
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if(ioctl(dev->fd,I2C_RDWR,(unsigned long)&iic_data)<0){
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LOGE("ioctl read error");
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}
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LOGI("IIC read HAL: %x", dataBuf[count]);
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count++;
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}
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return 0;
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}
注意:需打开设备/dev/i2c-1权限,否则会碰到Pemission
Denied错误。从源码根目录下进入system/core/rootdir目录,打开ueventd.rc 添加一行:/dev/i2c-1
0666 root root (这里设备各开发板可能不同)
3. 在iic目录下编写android.mk进行编译
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LOCAL_PATH := $(call my-dir)
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include $(CLEAR_VARS)
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LOCAL_MODULE_TAGS := optional
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LOCAL_PRELINK_MODULE := false
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LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw
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LOCAL_SRC_FILES := iic.c
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LOCAL_MODULE := iic.default
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include $(BUILD_SHARED_LIBRARY)
编译命令:mmm -B hardware/libhardware/module/iic 编译成功会得到iic.default.so,打包进img默认会被加载。
(待续)
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