一、i2c-dev驱动分析
1.1、设备驱动注册
分析这个驱动,还是从module_init()和module_exit()开始,程序如下:
-
static int __init i2c_dev_init(void)
-
{
-
int res;
-
printk(KERN_INFO "i2c /dev entries driver\n");
-
res = register_chrdev(I2C_MAJOR, "i2c", &i2cdev_fops);
-
if (res)
-
goto out;
-
i2c_dev_class = class_create(THIS_MODULE, "i2c-dev");
-
if (IS_ERR(i2c_dev_class)) {
-
res = PTR_ERR(i2c_dev_class);
-
goto out_unreg_chrdev;
-
}
-
/* Keep track of adapters which will be added or removed later */
-
res = bus_register_notifier(&i2c_bus_type, &i2cdev_notifier);
-
if (res)
-
goto out_unreg_class;
-
/* Bind to already existing adapters right away */
-
i2c_for_each_dev(NULL, i2cdev_attach_adapter);
-
return 0;
-
out_unreg_class:
-
class_destroy(i2c_dev_class);
-
out_unreg_chrdev:
-
unregister_chrdev(I2C_MAJOR, "i2c");
-
out:
-
printk(KERN_ERR "%s: Driver Initialisation failed\n", __FILE__);
-
return res;
-
}
-
static void __exit i2c_dev_exit(void)
-
{
-
bus_unregister_notifier(&i2c_bus_type, &i2cdev_notifier);
-
i2c_for_each_dev(NULL, i2cdev_detach_adapter);
-
class_destroy(i2c_dev_class);
-
unregister_chrdev(I2C_MAJOR, "i2c");
-
}
-
module_init(i2c_dev_init);
-
module_exit(i2c_dev_exit);
首先注册了i2cdev_fops操作函数集,接着注册了一个名为”i2c-dev”的class,然后又注册了一个i2cdev_notifier,i2cdev_notifier如下:
-
static struct notifier_block i2cdev_notifier = {
-
.notifier_call = i2cdev_notifier_call,
-
};
-
int i2cdev_notifier_call(struct notifier_block *nb, unsigned long action,
-
void *data)
-
{
-
struct device *dev = data;
-
-
switch (action) {
-
case BUS_NOTIFY_ADD_DEVICE:
-
return i2cdev_attach_adapter(dev, NULL);
-
case BUS_NOTIFY_DEL_DEVICE:
-
return i2cdev_detach_adapter(dev, NULL);
-
}
-
-
return 0;
-
}
紧接着看下i2cdev_attach_adapter函数:
-
static int i2cdev_attach_adapter(struct device *dev, void *dummy)
-
{
-
struct i2c_adapter *adap;
-
struct i2c_dev *i2c_dev;
-
int res;
-
if (dev->type != &i2c_adapter_type)
-
return 0;
-
adap = to_i2c_adapter(dev);
-
i2c_dev = get_free_i2c_dev(adap);
-
if (IS_ERR(i2c_dev))
-
return PTR_ERR(i2c_dev);
-
/* register this i2c device with the driver core */
-
i2c_dev->dev = device_create(i2c_dev_class, &adap->dev,
-
MKDEV(I2C_MAJOR, adap->nr), NULL,
-
"i2c-%d", adap->nr);
-
if (IS_ERR(i2c_dev->dev)) {
-
res = PTR_ERR(i2c_dev->dev);
-
goto error;
-
}
-
res = device_create_file(i2c_dev->dev, &dev_attr_name);
-
if (res)
-
goto error_destroy;
-
pr_debug("i2c-dev: adapter [%s] registered as minor %d\n",
-
adap->name, adap->nr);
-
return 0;
-
error_destroy:
-
device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));
-
error:
-
return_i2c_dev(i2c_dev);
-
return res;
-
}
这个函数也很简单,首先调用get_free_i2c_dev()分配并初始化了一个struct
i2c_dev结构,使i2c_dev->adap指向操作的adapter.之后,该i2c_dev会被链入链表i2c_dev_list中。再分别以I2C_MAJOR,、adap->nr为主次设备号创建了一个device。如果此时系统配置了udev或者是hotplug,那么就在/dev下自动创建相关的设备节点了。
i2cdev_detach_adapter函数完成相反的操作,在此省略。
所有主设备号为I2C_MAJOR的设备节点的操作函数是i2cdev_fops,它的定义如下所示:
-
static const struct file_operations i2cdev_fops = {
-
.owner = THIS_MODULE,
-
.llseek = no_llseek,
-
.read = i2cdev_read,
-
.write = i2cdev_write,
-
.unlocked_ioctl = i2cdev_ioctl,
-
.open = i2cdev_open,
-
.release = i2cdev_release,
-
};
接下来一一分析i2cdev_fops结构体的成员。
1.2、设备打开函数--i2cdev_open
-
static int i2cdev_open(struct inode *inode, struct file *file)
-
{
-
unsigned int minor = iminor(inode);
-
struct i2c_client *client;
-
struct i2c_adapter *adap;
-
struct i2c_dev *i2c_dev;
-
i2c_dev = i2c_dev_get_by_minor(minor); //以次设备号从i2c_dev_list链表中取得i2c_dev
-
if (!i2c_dev)
-
return -ENODEV;
-
adap = i2c_get_adapter(i2c_dev->adap->nr); //以apapter的总线号从i2c_adapter_idr中找到adapter
-
if (!adap)
-
return -ENODEV;
-
/* This creates an anonymous i2c_client, which may later be
-
* pointed to some address using I2C_SLAVE or I2C_SLAVE_FORCE.
-
*
-
* This client is ** NEVER REGISTERED ** with the driver model
-
* or I2C core It just holds private copies of addressing
-
* information and maybe a PEC flag.
-
*/
-
client = kzalloc(sizeof(*client), GFP_KERNEL); //分配并初始化一个i2c_client结构
-
if (!client) {
-
i2c_put_adapter(adap);
-
return -ENOMEM;
-
}
-
snprintf(client->name, I2C_NAME_SIZE, "i2c-dev %d", adap->nr);
-
client->adapter = adap; //clinet->adapter指向操作的adapter
-
file->private_data = client; //关联到file
-
return 0;
-
}
注意这里分配并初始化了一个struct
i2c_client结构,但是没有注册这个clinet。此外,这个函数中还有一个比较奇怪的操作,不是在前面已经将i2c_dev->adap
指向要操作的adapter么?为什么还要以adapter->nr为关键字从i2c_adapter_idr去找这个操作的adapter呢?因为调用i2c_get_adapter()从总线号nr找到操作的adapter的时候,还会增加module的引用计数,这样可以防止模块意外被释放掉,那
i2c_dev->adap->nr操作,如果i2c_dev->adap被释放掉的话,不是会引起系统崩溃么?这里因为在
i2cdev_attach_adapter()间接的增加了一次adapter的一次引用计数.如下:
-
static int i2cdev_attach_adapter(struct i2c_adapter *adap)
-
{
-
......
-
i2c_dev->dev = device_create(i2c_dev_class, &adap->dev,
-
MKDEV(I2C_MAJOR, adap->nr),
-
"i2c-%d", adap->nr);
-
......
-
}
i2c_dev内嵌的device是以adap->dev为父结点,在device_create()中会增次adap->dev的一次引用计数。
1.3、read操作
Read操作对应的操作函数如下示:
-
static ssize_t i2cdev_read (struct file *file, char __user *buf, size_t count,
-
loff_t *offset)
-
{
-
char *tmp;
-
int ret;
-
struct i2c_client *client = (struct i2c_client *)file->private_data;
-
if (count > 8192)
-
count = 8192;
-
tmp = kmalloc(count,GFP_KERNEL);
-
if (tmp==NULL)
-
return -ENOMEM;
-
pr_debug("i2c-dev: i2c-%d reading %zd bytes./n",
-
iminor(file->f_path.dentry->d_inode), count);
-
ret = i2c_master_recv(client,tmp,count);
-
if (ret >= 0)
-
ret = copy_to_user(buf,tmp,count)?-EFAULT:ret;
-
kfree(tmp);
-
return ret;
-
}
首先从file结构中取得struct i2c_clinet,然后在kernel分配相同长度的缓存区,随之调用i2c_master_recv()从设备中读取数据.再将读取出来的数据copy到用户空间中。I2c_master_recv()在《Linux I2C驱动分析(二)----I2C板级设备扫描和数据传输》已经讲述。
1.4、write操作
-
static ssize_t i2cdev_write(struct file *file, const char __user *buf,
-
size_t count, loff_t *offset)
-
{
-
int ret;
-
char *tmp;
-
struct i2c_client *client = file->private_data;
-
-
if (count > 8192)
-
count = 8192;
-
-
tmp = memdup_user(buf, count);
-
if (IS_ERR(tmp))
-
return PTR_ERR(tmp);
-
-
pr_debug("i2c-dev: i2c-%d writing %zu bytes.\n",
-
iminor(file->f_path.dentry->d_inode), count);
-
-
ret = i2c_master_send(client, tmp, count);
-
kfree(tmp);
-
return ret;
-
}
该操作比较简单,就是将用户空间的数据通过使用函数i2c_master_send发送到i2c 设备。i2c_master_send函数在《Linux I2C驱动分析(二)----I2C板级设备扫描和数据传输》已经讲述。
memdup_user函数完成分配存储区,把应用层的数据复制到刚分配的存储区中,具体程序如下:
-
void *memdup_user(const void __user *src, size_t len)
-
{
-
void *p;
-
/*
-
* Always use GFP_KERNEL, since copy_from_user() can sleep and
-
* cause pagefault, which makes it pointless to use GFP_NOFS
-
* or GFP_ATOMIC.
-
*/
-
p = kmalloc_track_caller(len, GFP_KERNEL);
-
if (!p)
-
return ERR_PTR(-ENOMEM);
-
if (copy_from_user(p, src, len)) {
-
kfree(p);
-
return ERR_PTR(-EFAULT);
-
}
-
return p;
-
}
1.5、 ioctl函数
有人可能看出了一个问题,clinet->addr是从哪来的呢?对,在read之前应该还要有一步操作来设置
clinet->addr的值。这个过程是ioctl的操作,ioctl可以设置PEC标志,重试次数,超时时间和发送接收数据等。具体程序如下:
-
static long i2cdev_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
-
{
-
struct i2c_client *client = file->private_data;
-
unsigned long funcs;
-
dev_dbg(&client->adapter->dev, "ioctl, cmd=0x%02x, arg=0x%02lx\n",
-
cmd, arg);
-
switch (cmd) {
-
case I2C_SLAVE:
-
case I2C_SLAVE_FORCE:
-
/* NOTE: devices set up to work with "new style" drivers
-
* can't use I2C_SLAVE, even when the device node is not
-
* bound to a driver. Only I2C_SLAVE_FORCE will work.
-
*
-
* Setting the PEC flag here won't affect kernel drivers,
-
* which will be using the i2c_client node registered with
-
* the driver model core. Likewise, when that client has
-
* the PEC flag already set, the i2c-dev driver won't see
-
* (or use) this setting.
-
*/
-
if ((arg > 0x3ff) ||
-
(((client->flags & I2C_M_TEN) == 0) && arg > 0x7f))
-
return -EINVAL;
-
if (cmd == I2C_SLAVE && i2cdev_check_addr(client->adapter, arg))
-
return -EBUSY;
-
/* REVISIT: address could become busy later */
-
client->addr = arg; //设置addr
-
return 0;
-
case I2C_TENBIT:
-
//设置10 bit地址模式
-
if (arg)
-
client->flags |= I2C_M_TEN;
-
else
-
client->flags &= ~I2C_M_TEN;
-
return 0;
-
case I2C_PEC:
-
//设置传输后增加PEC标志
-
if (arg)
-
client->flags |= I2C_CLIENT_PEC;
-
else
-
client->flags &= ~I2C_CLIENT_PEC;
-
return 0;
-
case I2C_FUNCS:
-
//获取函数支持
-
funcs = i2c_get_functionality(client->adapter);
-
return put_user(funcs, (unsigned long __user *)arg);
-
case I2C_RDWR:
-
//读取和接收数据,后面讲述
-
return i2cdev_ioctl_rdrw(client, arg);
-
case I2C_SMBUS:
-
//smbus协议数据传输,后面讲述
-
return i2cdev_ioctl_smbus(client, arg);
-
case I2C_RETRIES:
-
//设置重试次数
-
client->adapter->retries = arg;
-
break;
-
case I2C_TIMEOUT:
-
/* For historical reasons, user-space sets the timeout
-
* value in units of 10 ms.
-
*/
-
//设置超时时间
-
client->adapter->timeout = msecs_to_jiffies(arg * 10);
-
break;
-
default:
-
/* NOTE: returning a fault code here could cause trouble
-
* in buggy userspace code. Some old kernel bugs returned
-
* zero in this case, and userspace code might accidentally
-
* have depended on that bug.
-
*/
-
return -ENOTTY;
-
}
-
return 0;
-
}
读取和接收数据函数i2cdev_ioctl_rdrw(client, arg);如下:
-
static noinline int i2cdev_ioctl_rdrw(struct i2c_client *client,
-
unsigned long arg)
-
{
-
struct i2c_rdwr_ioctl_data rdwr_arg; //包括i2c_msg和它的个数
-
struct i2c_msg *rdwr_pa;
-
u8 __user **data_ptrs;
-
int i, res;
-
if (copy_from_user(&rdwr_arg,
-
(struct i2c_rdwr_ioctl_data __user *)arg,
-
sizeof(rdwr_arg)))
-
return -EFAULT;
-
/* Put an arbitrary limit on the number of messages that can
-
* be sent at once */
-
if (rdwr_arg.nmsgs > I2C_RDRW_IOCTL_MAX_MSGS)
-
return -EINVAL;
-
rdwr_pa = kmalloc(rdwr_arg.nmsgs * sizeof(struct i2c_msg), GFP_KERNEL); //创建存储i2c_msg的内存
-
if (!rdwr_pa)
-
return -ENOMEM;
-
if (copy_from_user(rdwr_pa, rdwr_arg.msgs,
-
rdwr_arg.nmsgs * sizeof(struct i2c_msg))) {
-
kfree(rdwr_pa);
-
return -EFAULT;
-
}
-
data_ptrs = kmalloc(rdwr_arg.nmsgs * sizeof(u8 __user *), GFP_KERNEL);
-
if (data_ptrs == NULL) {
-
kfree(rdwr_pa);
-
return -ENOMEM;
-
}
-
res = 0;
-
for (i = 0; i < rdwr_arg.nmsgs; i++) {
-
/* Limit the size of the message to a sane amount;
-
* and don't let length change either. */
-
if ((rdwr_pa[i].len > 8192) ||
-
(rdwr_pa[i].flags & I2C_M_RECV_LEN)) {
-
res = -EINVAL;
-
break;
-
}
-
data_ptrs[i] = (u8 __user *)rdwr_pa[i].buf;
-
rdwr_pa[i].buf = memdup_user(data_ptrs[i], rdwr_pa[i].len);
-
if (IS_ERR(rdwr_pa[i].buf)) {
-
res = PTR_ERR(rdwr_pa[i].buf);
-
break;
-
}
-
}
-
if (res < 0) {
-
int j;
-
for (j = 0; j < i; ++j)
-
kfree(rdwr_pa[j].buf);
-
kfree(data_ptrs);
-
kfree(rdwr_pa);
-
return res;
-
}
-
res = i2c_transfer(client->adapter, rdwr_pa, rdwr_arg.nmsgs); //传输数据
-
while (i-- > 0) {
-
if (res >= 0 && (rdwr_pa[i].flags & I2C_M_RD)) {
-
if (copy_to_user(data_ptrs[i], rdwr_pa[i].buf,
-
rdwr_pa[i].len)) //将接收到的数据发送到应用层
-
res = -EFAULT;
-
}
-
kfree(rdwr_pa[i].buf);
-
}
-
kfree(data_ptrs);
-
kfree(rdwr_pa);
-
return res;
-
}
smbus协议数据传输函数i2cdev_ioctl_smbus(client, arg);如下:
-
static noinline int i2cdev_ioctl_smbus(struct i2c_client *client,
-
unsigned long arg)
-
{
-
struct i2c_smbus_ioctl_data data_arg;
-
union i2c_smbus_data temp;
-
int datasize, res;
-
//从应用层复制数据
-
if (copy_from_user(&data_arg,
-
(struct i2c_smbus_ioctl_data __user *) arg,
-
sizeof(struct i2c_smbus_ioctl_data)))
-
return -EFAULT;
-
if ((data_arg.size != I2C_SMBUS_BYTE) &&
-
(data_arg.size != I2C_SMBUS_QUICK) &&
-
(data_arg.size != I2C_SMBUS_BYTE_DATA) &&
-
(data_arg.size != I2C_SMBUS_WORD_DATA) &&
-
(data_arg.size != I2C_SMBUS_PROC_CALL) &&
-
(data_arg.size != I2C_SMBUS_BLOCK_DATA) &&
-
(data_arg.size != I2C_SMBUS_I2C_BLOCK_BROKEN) &&
-
(data_arg.size != I2C_SMBUS_I2C_BLOCK_DATA) &&
-
(data_arg.size != I2C_SMBUS_BLOCK_PROC_CALL)) {
-
dev_dbg(&client->adapter->dev,
-
"size out of range (%x) in ioctl I2C_SMBUS.\n",
-
data_arg.size);
-
return -EINVAL; //不符合协议,直接退出
-
}
-
/* Note that I2C_SMBUS_READ and I2C_SMBUS_WRITE are 0 and 1,
-
so the check is valid if size==I2C_SMBUS_QUICK too. */
-
if ((data_arg.read_write != I2C_SMBUS_READ) &&
-
(data_arg.read_write != I2C_SMBUS_WRITE)) {
-
dev_dbg(&client->adapter->dev,
-
"read_write out of range (%x) in ioctl I2C_SMBUS.\n",
-
data_arg.read_write);
-
return -EINVAL; //既不是读,也不是写
-
}
-
/* Note that command values are always */
-
if ((data_arg.size == I2C_SMBUS_QUICK) ||
-
((data_arg.size == I2C_SMBUS_BYTE) &&
-
(data_arg.read_write == I2C_SMBUS_WRITE)))
-
/* These are special: we do not use data */
-
return i2c_smbus_xfer(client->adapter, client->addr,
-
client->flags, data_arg.read_write,
-
data_arg.command, data_arg.size, NULL); //不需要读
-
if (data_arg.data == NULL) {
-
dev_dbg(&client->adapter->dev,
-
"data is NULL pointer in ioctl I2C_SMBUS.\n");
-
return -EINVAL;
-
}
-
//判断数据大小
-
if ((data_arg.size == I2C_SMBUS_BYTE_DATA) ||
-
(data_arg.size == I2C_SMBUS_BYTE))
-
datasize = sizeof(data_arg.data->byte);
-
else if ((data_arg.size == I2C_SMBUS_WORD_DATA) ||
-
(data_arg.size == I2C_SMBUS_PROC_CALL))
-
datasize = sizeof(data_arg.data->word);
-
else /* size == smbus block, i2c block, or block proc. call */
-
datasize = sizeof(data_arg.data->block);
-
if ((data_arg.size == I2C_SMBUS_PROC_CALL) ||
-
(data_arg.size == I2C_SMBUS_BLOCK_PROC_CALL) ||
-
(data_arg.size == I2C_SMBUS_I2C_BLOCK_DATA) ||
-
(data_arg.read_write == I2C_SMBUS_WRITE)) {
-
if (copy_from_user(&temp, data_arg.data, datasize))
-
return -EFAULT;
-
}
-
if (data_arg.size == I2C_SMBUS_I2C_BLOCK_BROKEN) {
-
/* Convert old I2C block commands to the new
-
convention. This preserves binary compatibility. */
-
data_arg.size = I2C_SMBUS_I2C_BLOCK_DATA;
-
if (data_arg.read_write == I2C_SMBUS_READ)
-
temp.block[0] = I2C_SMBUS_BLOCK_MAX;
-
}
-
//smbus数据传输,2中已经讲述
-
res = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
-
data_arg.read_write, data_arg.command, data_arg.size, &temp);
-
if (!res && ((data_arg.size == I2C_SMBUS_PROC_CALL) ||
-
(data_arg.size == I2C_SMBUS_BLOCK_PROC_CALL) ||
-
(data_arg.read_write == I2C_SMBUS_READ))) {
-
if (copy_to_user(data_arg.data, &temp, datasize))
-
return -EFAULT;
-
}
-
return res;
-
}
二、 用户空间使用i2c_dev
对于注册的i2c适配器,用户空间可以使用它们。上面的驱动对每个适配器生成一个主设备号为89的设备节点,实现了文件操作接口,用户空间可以通过i2c设备节点访问i2c适配器。适配器的编号从0开始,和适配器的设备节点的次设备号相同。i2c适配器的设备节点是/dev/i2c-x,其中x是数字,代表适配器的编号。由于适配器编号是动态分配的(和注册次序有关),所以想了解哪一个适配器对应什么编号,可以查看/sys/class/i2c-dev/目录下的文件内容。
2.1 前期准备
为了在用户空间的程序当中操作i2c适配器,必须在程序中包含以下两句:
-
#include<linux/i2c-dev.h>
-
#include<linux/i2c.h>
这两个头文件中定义了之后需要用到的结构体和宏。然后就可以打开设备节点了。但是打开哪一个呢?因为适配器的编号并不固定。为此我们在终端中运行以下命令:
[root@hdw /]# cat /sys/class/i2c-dev/i2c-0/name
BLX GSC3280 I2C adapter
如果我们想打开第二个适配器,刚好它的编号是1,对应的设备节点是/dev/i2c-1。那么可以用下面的方法打开它:
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int fd;
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if ((fd = open("/dev/i2c-1",O_RDWR))< 0)
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{
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/* 错误处理 */
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exit(1);
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}
打开适配器对应的设备节点,i2c-dev为打开的线程建立一个i2c_client,但是这个i2c_client并不加到i2c_adapter的client链表当中。当用户关闭设备节点时,它自动被释放。
2.2 IOCTL控制
查看include/linux/i2c-dev.h文件,可以看到i2c-dev支持的IOCTL命令。如下:
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#define I2C_RETRIES 0x0701 /* 设置收不到ACK时的重试次数 */
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#define I2C_TIMEOUT 0x0702 /* 设置超时时限的jiffies */
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#define I2C_SLAVE 0x0703 /* 设置从机地址 */
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#define I2C_SLAVE_FORCE 0x0706 /* 强制设置从机地址 */
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#define I2C_TENBIT 0x0704 /* 选择地址位长:=0 for 7bit , != 0 for 10 bit */
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#define I2C_FUNCS 0x0705 /* 获取适配器支持的功能 */
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#define I2C_RDWR 0x0707 /* Combined R/W transfer (one STOP only) */
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#define I2C_PEC 0x0708 /* != 0 to use PEC with SMBus */
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#define I2C_SMBUS 0x0720 /* SMBus transfer */
下面进行一一解释。
1.设置重试次数
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ioctl(fd, I2C_RETRIES, m); //这句话设置适配器收不到ACK时重试的次数为m。默认的重试次数为1。
2.设置超时
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ioctl(fd, I2C_TIMEOUT, m); //设置SMBus的超时时间为m,单位为jiffies。
3.设置从机地址
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ioctl(fd, I2C_SLAVE,addr);
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ioctl(fd, I2C_SLAVE_FORCE, addr);
在调用read()和write()函数之前必须设置从机地址。这两行都可以设置从机的地址,区别是第二行无论内核中是否已有驱动在使用这个地址都会成功,
第一行则只在该地址空闲的情况下成功。由于i2c-dev创建的i2c_client不加入i2c_adapter的client列表,所以不能防止其它线程使用同一地址,也不能防止驱动模块占用同一地址。
4.设置地址模式
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ioctl(file, I2C_TENBIT, select); //如果select不等于0选择10比特地址模式,如果等于0选择7比特模式,默认7比特。只有适配器支持I2C_FUNC_10BIT_ADDR,这个请求才是有效的。
5.获取适配器功能
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ioctl(file, I2C_FUNCS, (unsignedlong *)funcs); //获取的适配器功能保存在funcs中。各比特的含义如:
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/* include/linux/i2c.h */
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#define I2C_FUNC_I2C 0x00000001
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#define I2C_FUNC_10BIT_ADDR 0x00000002
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#define I2C_FUNC_PROTOCOL_MANGLING 0x00000004 /* I2C_M_{REV_DIR_ADDR,NOSTART,..} */
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#define I2C_FUNC_SMBUS_PEC 0x00000008
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#define I2C_FUNC_SMBUS_BLOCK_PROC_CALL 0x00008000 /* SMBus 2.0 */
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#define I2C_FUNC_SMBUS_QUICK 0x00010000
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#define I2C_FUNC_SMBUS_READ_BYTE 0x00020000
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#define I2C_FUNC_SMBUS_WRITE_BYTE 0x00040000
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#define I2C_FUNC_SMBUS_READ_BYTE_DATA 0x00080000
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#define I2C_FUNC_SMBUS_WRITE_BYTE_DATA 0x00100000
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#define I2C_FUNC_SMBUS_READ_WORD_DATA 0x00200000
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#define I2C_FUNC_SMBUS_WRITE_WORD_DATA 0x00400000
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#define I2C_FUNC_SMBUS_PROC_CALL 0x00800000
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#define I2C_FUNC_SMBUS_READ_BLOCK_DATA 0x01000000
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#define I2C_FUNC_SMBUS_WRITE_BLOCK_DATA 0x02000000
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#define I2C_FUNC_SMBUS_READ_I2C_BLOCK 0x04000000 /* I2C-like block xfer */
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#define I2C_FUNC_SMBUS_WRITE_I2C_BLOCK 0x08000000 /* w/ 1-byte reg. addr. */
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#define I2C_FUNC_SMBUS_READ_I2C_BLOCK_2 0x10000000 /* I2C-like block xfer */
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#define I2C_FUNC_SMBUS_WRITE_I2C_BLOCK_2 0x20000000 /* w/ 2-byte reg. addr. */
6. I2C层通信
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ioctl(file, I2C_RDWR, (structi2c_rdwr_ioctl_data *)msgset);
这一行代码可以使用I2C协议和设备进行通信。它进行连续的读写,中间没有间歇。只有当适配器支持I2C_FUNC_I2C此命令才有效。参数是一个指针,指向一个结构体,它的定义如:
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struct i2c_rdwr_ioctl_data {
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struct i2c_msg __user *msgs; /* 指向i2c_msgs数组 */
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__u32nmsgs; /* 消息的个数 */
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};
msgs[] 数组成员包含了指向各自缓冲区的指针。这个函数会根据是否在消息中的flags置位I2C_M_RD来对缓冲区进行读写。从机的地址以及是否使用10比特地址模式记录在每个消息中,忽略之前ioctl设置的结果。
7.设置SMBus PEC
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ioctl(file, I2C_PEC, (long )select);
如果select不等于0选择SMBus PEC (packet error checking),等于零则关闭这个功能,默认是关闭的。
这个命令只对SMBus传输有效。这个请求只在适配器支持I2C_FUNC_SMBUS_PEC时有效;如果不支持这个命令也是安全的,它不做任何工作。
8.SMBus通信
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ioctl(file, I2C_SMBUS, (i2c_smbus_ioctl_data*)msgset);
这个函数和I2C_RDWR类似,参数的指针指向i2c_smbus_ioctl_data类型的变量,它的定义如:
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struct i2c_smbus_ioctl_data {
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__u8read_write;
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__u8command;
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__u32size;
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unioni2c_smbus_data __user *data;
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};
2.3 i2c_dev使用例程
要想在用户空间使用i2c适配器,首先要选择某个适配器的设备节点打开,然后才能进行通信。
2.3.1 read()/write()
通信的方式有两种,一种是使用操作普通文件的接口read()和write()。这两个函数间接调用了i2c_master_recv和
i2c_master_send。但是在使用之前需要使用I2C_SLAVE设置从机地址,设置可能失败,需要检查返回值。这种通信过程进行I2C层的通信,一次只能进行一个方向的传输。
下面的程序是ARM与E2PROM芯片通信的例子,使用read()/write()与i2c设备通信:
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#include <stdio.h>
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#include <sys/ioctl.h>
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#include <fcntl.h>
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#include <linux/i2c-dev.h>
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#include <linux/i2c.h>
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#define CHIP "/dev/i2c-0"
#define CHIP_ADDR 0x50
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-
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int main()
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{
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printf("this is i2c test/n");
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int fd =open(CHIP, O_RDWR);
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if (fd< 0) {
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printf("open"CHIP"failed/n");
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gotoexit;
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-
}
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if (ioctl(fd, I2C_SLAVE_FORCE, CHIP_ADDR) < 0) {
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/* 设置芯片地址 */
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printf("oictl:setslave address failed/n");
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goto close;
-
-
}
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struct i2c_msg msg;
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unsigned char rddata;
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unsigned char rdaddr[2] = {0, 0}; /* 将要读取的数据在芯片中的偏移量 */
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unsigned char wrbuf[3] = {0, 0, 0x3c}; /* 要写的数据,头两字节为偏移量 */
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printf("inputa char you want to write to E2PROM/n");
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wrbuf[2]= getchar();
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printf("writereturn:%d, write data:%x/n", write(fd, wrbuf, 3), wrbuf[2]);
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sleep(1);
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printf("writeaddress return: %d/n",write(fd, rdaddr, 2)); /* 读取之前首先设置读取的偏移量 */
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printf("readdata return:%d/n", read(fd, &rddata, 1));
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printf("rddata:%c/n", rddata);
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close:
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close(fd);
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exit:
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return0;
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}
1.3.2 I2C_RDWR
还可以使用I2C_RDWR实现同样的功能,使用I2C_RDWR与I2C设备通信
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#include <stdio.h>
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#include <sys/ioctl.h>
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#include <fcntl.h>
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#include <linux/i2c-dev.h>
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#include <linux/i2c.h>
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#define CHIP "/dev/i2c-0"
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#define CHIP_ADDR 0x50
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int main()
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{
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printf("hello,this is i2c tester/n");
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int fd =open(CHIP, O_RDWR);
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if (fd< 0) {
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printf("open"CHIP"failed/n");
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gotoexit;
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}
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struct i2c_msg msg;
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unsigned char rddata;
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unsigned char rdaddr[2] = {0, 0};
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unsigned char wrbuf[3] = {0, 0, 0x3c};
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printf("inputa char you want to write to E2PROM/n");
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wrbuf[2]= getchar();
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struct i2c_rdwr_ioctl_data ioctl_data;
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struct i2c_msg msgs[2];
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msgs[0].addr= CHIP_ADDR;
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msgs[0].len= 3;
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msgs[0].buf= wrbuf;
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ioctl_data.nmsgs= 1;
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ioctl_data.msgs= &msgs[0];
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printf("ioctlwrite,return :%d/n", ioctl(fd, I2C_RDWR, &ioctl_data));
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sleep(1);
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msgs[0].addr= CHIP_ADDR;
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msgs[0].len= 2;
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msgs[0].buf= rdaddr;
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msgs[1].addr= CHIP_ADDR;
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msgs[1].flags|= I2C_M_RD;
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msgs[1].len= 1;
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msgs[1].buf= &rddata;
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ioctl_data.nmsgs= 1;
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ioctl_data.msgs= msgs;
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printf("ioctlwrite address, return :%d/n", ioctl(fd, I2C_RDWR, &ioctl_data));
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ioctl_data.msgs= &msgs[1];
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printf("ioctlread, return :%d/n", ioctl(fd, I2C_RDWR, &ioctl_data));
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printf("rddata:%c/n", rddata);
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close:
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close(fd);
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exit:
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return0;
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}
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