1. MMA7660芯片介绍
MMA7660FC 是 ± 1.5 克三轴数字输出，超低功率，紧凑型电容微电机三轴加速度计，功耗很低，容量很小MEMS 传感器。具有偏移和增益误差补偿补偿偏移和增益误差，以及用户可以将其转换为 6 位分辨率和输出速率。MMA7660芯片可以中断引脚（INT）向外通知传感器数据变化、方向、姿态识别等信息。.4V 至 3.6V，数字工作电压范围 1.71V 到 3.6V 。常用于手机、手持电脑、车载导航、便携式电脑防盗、自动自行车刹车灯、运动检测手镯、数码机、自动叫醒闹钟等。
特别是步骤计算的功能现在是最常见的，智能手镯和手机都有三轴加速度计，可以记录每天的步数，计算运动量等。现在很多不倒翁、无人机、相机云台，很多常见的产品都能看到三轴加速度计。
通过MMA7660可以做出很多项目： 比如: 老人防跌倒手环、自行车自动刹车灯，智能闹钟，烤火炉跌倒自动断电、运动手环等等。
本文介绍了如何介绍这篇文章Linux下编写MMA由7660三轴加速芯片驱动，读取当前芯片的方向和姿态，获得X,Y,Z三轴数据。MMA7660是IIC当前驱动器采用标准接口IIC使用字符设备框架将获得的数据传输到应用层的子系统编写驱动器。
2. 硬件连线
目前使用的开发板是友好之臂Tiny三星4412开发板EXYNOS4412芯片，板本身有一个MMA芯片原理图如下：
内核本身有MMA7660驱动，以下是源码路径：
假如加载自己编写的驱动，还需要去掉原来内核自带的驱动，否则无法匹配。
Device Drivers ---> <*> Hardware Monitoring support ---> <*> Freescale MMA7660 Accelerometer (将*删除编译内核和烧写内核)
3. 源代码
3.1 mma7660设备端代码： IIC子系统
#include <linux/init.h>#include <linux/module.h>#include <linux/platform_device.h>#include <linux/i2c.h>#include <linux/gpio.h>#include <mach/gpio.h>#include <plat/gpio-cfg.h>static struct i2c_client *i2cClient = NULL;static unsigned short i2c_addr_list[]= { 0x4c, I2C_CLIENT_END};/*地址队列*//*1. 获取控制器(总线)2. 探测设备是否存在3. 定义一个名字用于找到驱动端 */static int __init mma7660_dev_init(void){
/*mach-tiny4412.c*/ struct i2c_adapter *i2c_adap=NULL; /*获取到的总线存放在这个结构体*/ struct i2c_board_info i2c_info; /*设备描述结构体，里面存放着设备的名字还有地址*/ /*1. 获取IIC控制器*/ i2c_adap = i2c_get_adapter(3); /*要使用IIC_3号总线*/ if(!i2c_adap) {
printk("获取IIC控制器信息失败!\n"); return -1; } memset(&i2c_info,0,sizeof(struct i2c_board_info)); /*清空结构体*/ strlcpy(i2c_info.type,"mma7660_drv",I2C_NAME_SIZE); /*名称的赋值*/ i2c_info.irq=EXYNOS4_GPX3(1); /*中断IO口*/ /*2. 创建IIC设备客户端*/ i2cClient = i2c_new_probed_device(i2c_adap,&i2c_info,i2c_addr_list,NULL); if(!i2cClient) {
printk("mma7660_探测地址出现错误!!\n"); return -1; } i2c_put_adapter(i2c_adap);/*设置模块使用计数*/ printk("mma7660_dev_init!!\n"); return 0;}static void __exit mma7660_dev_exit(void)//平台设备端的出口函数{
printk(" mma7660_dev_exit ok!!\n"); /*注销设备*/ i2c_unregister_device(i2cClient); /*释放*/ i2c_release_client(i2cClient);}module_init(mma7660_dev_init);module_exit(mma7660_dev_exit);MODULE_LICENSE("GPL");3.2 mma7660驱动端代码: IIC子系统
#include <linux/init.h>#include <linux/module.h>#include <linux/platform_device.h>#include <linux/i2c.h>#include <linux/irq.h>#include <linux/interrupt.h>#include <linux/gpio.h>#include <mach/gpio.h>#include <plat/gpio-cfg.h>#include <linux/workqueue.h>#include <linux/delay.h>/* MMA7760 Registers */#define MMA7660_XOUT 0x00 // 6-bit output value X#define MMA7660_YOUT 0x01 // 6-bit output value Y#define MMA7660_ZOUT 0x02 // 6-bit output value Z#define MMA7660_TILT 0x03 // Tilt status#define MMA7660_SRST 0x04 // Sampling Rate Status#define MMA7660_SPCNT 0x05 // Sleep Count#define MMA7660_INTSU 0x06 // Interrupt Setup#define MMA7660_MODE 0x07 // Mode#define MMA7660_SR 0x08 // Auto-Wake/Sleep and Debounce Filter#define MMA7660_PDET 0x09 // Tap Detection#define MMA7660_PD 0x0a // Tap Debounce Countstatic const struct i2c_device_id mma7660_id[] ={
{
"mma7660_drv",0}, /*设备端的名字,0表示不需要私有数据*/ {
}};static u32 mma7660_irq; /*触摸屏的中断编号*/static struct i2c_client *mma7660_client=NULL;static int last_tilt = 0;#define __need_retry(__v) (__v & (1 << 6))#define __is_negative(__v) (__v & (1 << 5))static const char *mma7660_bafro[] = {
"未知", "前面", "背面"};static const char *mma7660_pola[] = {
"未知", "左面", "向右", "保留", "保留", "向下", "向上", "保留",};/*函数功能：读取一个字节的数据*/static int mma7660_read_tilt(struct i2c_client *client, int *tilt){
int val; do {
val = i2c_smbus_read_byte_data(client, MMA7660_TILT); } while (__need_retry(val)); *tilt = (val & 0xff); return 0;}/*函数功能: 读取XYZ坐标数据*/static int mma7660_read_xyz(struct i2c_client *client, int idx, int *xyz){
int val; do {
val = i2c_smbus_read_byte_data(client, idx + MMA7660_XOUT); } while (__need_retry(val)); *xyz = __is_negative(val) ? (val | ~0x3f) : (val & 0x3f); return 0;}/*工作队列处理函数*/static void mma7660_worker(struct work_struct *work){
int bafro, pola, shake, tap; int val = 0; mma7660_read_tilt(mma7660_client,&val); /* TODO: report it ? */ bafro = val & 0x03; if (bafro != (last_tilt & 0x03)) {
printk("%s\n", mma7660_bafro[bafro]); } pola = (val >> 2) & 0x07; if (pola != ((last_tilt >> 2) & 0x07)) {
printk("%s\n", mma7660_pola[pola]); } shake = (val >> 5) & 0x01; if (shake && shake != ((last_tilt >> 5) & 0x01)) {
printk("Shake\n"); } tap = (val >> 7) & 0x01; if (tap && tap != ((last_tilt >> 7) & 0x01)) {
printk("Tap\n"); } /* Save current status */ last_tilt = val; int axis[3]; int i; for (i = 0; i < 3; i++) {
mma7660_read_xyz(mma7660_client, i, &axis[i]); } printk("ABS_X=%d\n",axis[0]); printk("ABS_Y=%d\n",axis[1]); printk("ABS_Z=%d\n",axis[2]);}/*函数功能: mma7660初始化*/static int mma7660_initialize(struct i2c_client *client){
int val; /* Using test mode to probe chip */ i2c_smbus_write_byte_data(client, MMA7660_MODE, 0x00); mdelay(10); i2c_smbus_write_byte_data(client, MMA7660_MODE, 0x04); mdelay(10); i2c_smbus_write_byte_data(client, MMA7660_XOUT, 0x3f); i2c_smbus_write_byte_data(client, MMA7660_YOUT, 0x01); i2c_smbus_write_byte_data(client, MMA7660_ZOUT, 0x15); val = i2c_smbus_read_byte_data(client, MMA7660_ZOUT); if (val != 0x15) {
dev_err(&client->dev, "no device\n"); return -ENODEV; } /* Goto standby mode for configuration */ i2c_smbus_write_byte_data(client, MMA7660_MODE, 0x00); mdelay(10); /* Sample rate: 64Hz / 16Hz; Filt: 3 samples */ i2c_smbus_write_byte_data(client, MMA7660_SR, ((2<<5) | (1<<3) | 1)); /* Sleep count */ i2c_smbus_write_byte_data(client, MMA7660_SPCNT, 0xA0); /* Tap detect and debounce ~4ms */ i2c_smbus_write_byte_data(client, MMA7660_PDET, 4); i2c_smbus_write_byte_data(client, MMA7660_PD, 15); /* Enable interrupt except exiting Auto-Sleep */ i2c_smbus_write_byte_data(client, MMA7660_INTSU, 0xe7); /* IPP, Auto-wake, auto-sleep and standby */ i2c_smbus_write_byte_data(client, MMA7660_MODE, 0x59); mdelay(10); /* Save current tilt status */ mma7660_read_tilt(client, &last_tilt); mma7660_client = client; return 0;}/*静态方式初始化工作队列*/DECLARE_WORK(mma7660_work,mma7660_worker);static irqreturn_t mma7660_interrupt(int irq, void *dev_id){
/*调度共享工作队列*/ schedule_work(&mma7660_work); return IRQ_HANDLED;}/*匹配成功时调用*/static int mma7660_probe(struct i2c_client *client, const struct i2c_device_id *device_id){
printk("mma7660_probe!!!\n"); printk("驱动端IIC匹配的地址=0x%x\n",client->addr); mma7660_client=client; /*1. 注册中断*/ mma7660_irq=gpio_to_irq(client->irq);/*获取中断编号*/ if(request_irq(mma7660_irq,mma7660_interrupt,IRQF_TRIGGER_FALLING,"mma7660_irq",NULL)!=0) {
printk("mma7660_中断注册失败!\n"); } /*2. 初始化mma7660*/ if(mma7660_initialize(client) < 0) {
printk(" 初始化mma7660失败!\n"); } return 0;}static int mma7660_remove(struct i2c_client *client){
free_irq(mma7660_irq,NULL); printk("mma7660_remove!!!\n"); return 0;}struct i2c_driver i2c_drv ={
.driver = {
.name = "mma7660", .owner = THIS_MODULE, }, .probe = mma7660_probe, //探测函数 .remove = mma7660_remove, //资源卸载 .id_table = mma7660_id, //里面有一个名字的参数用来匹配设备端名字};static int __init mma7660_drv_init(void){
/*向iic总线注册一个驱动*/ i2c_add_driver(&i2c_drv); return 0;}static void __exit mma7660_drv_exit(void){
/*从iic总线注销一个驱动*/ i2c_del_driver(&i2c_drv);}module_init(mma7660_drv_init);module_exit(mma7660_drv_exit);MODULE_LICENSE("GPL");