用c语言设置I2C的读写

Question

首先，我在这方面是新手，但我正在学习，真的想让它工作起来。我买了一台树莓机和一台bno055博世加速计。它附带了一个bno055.c、bno055.h和一个bno055_support.c文件。在学习了编程和c语言并学习/尝试之后，我似乎需要以某种方式定义如何进行I2C读写。需要对其进行设置，以便您可以定义读取/写入的字节数。您可以在下面找到两个预定义的函数：

/*  \Brief: The API is used as I2C bus write
 *  \Return : Status of the I2C write
 *  \param dev_addr : The device address of the sensor
 *  \param reg_addr : Address of the first register,
 *   will data is going to be written
 *  \param reg_data : It is a value hold in the array,
 *      will be used for write the value into the register
 *  \param cnt : The no of byte of data to be write
 */
s8 BNO055_I2C_bus_write(u8 dev_addr, u8 reg_addr, u8 *reg_data, u8 cnt)
{
    s32 BNO055_iERROR = BNO055_INIT_VALUE;
    u8 array[I2C_BUFFER_LEN];
    u8 stringpos = BNO055_INIT_VALUE;

    array[BNO055_INIT_VALUE] = reg_addr;
    for (stringpos = BNO055_INIT_VALUE; stringpos < cnt; stringpos++)
        array[stringpos + BNO055_I2C_BUS_WRITE_ARRAY_INDEX] =
            *(reg_data + stringpos);
    }
    /*
    * Please take the below APIs as your reference for
    * write the data using I2C communication
    * "BNO055_iERROR = I2C_WRITE_STRING(DEV_ADDR, ARRAY, CNT+1)"
    * add your I2C write APIs here
    * BNO055_iERROR is an return value of I2C read API
    * Please select your valid return value
    * In the driver BNO055_SUCCESS defined as 0
    * and FAILURE defined as -1
    * Note :
    * This is a full duplex operation,
    * The first read data is discarded, for that extra write operation
    * have to be initiated. For that cnt+1 operation done
    * in the I2C write string function
    * For more information please refer data sheet SPI communication:
    */
    return (s8)BNO055_iERROR;
}

 /* \Brief: The API is used as I2C bus read
 *  \Return : Status of the I2C read
 *  \param dev_addr : The device address of the sensor
 *  \param reg_addr : Address of the first register,
 *  will data is going to be read
 *  \param reg_data : This data read from the sensor,
 *   which is hold in an array
 *  \param cnt : The no of byte of data to be read
 */
s8 BNO055_I2C_bus_read(u8 dev_addr, u8 reg_addr, u8 *reg_data, u8 cnt)
{
    s32 BNO055_iERROR = BNO055_INIT_VALUE;
    u8 array[I2C_BUFFER_LEN] = {BNO055_INIT_VALUE};
    u8 stringpos = BNO055_INIT_VALUE;

    array[BNO055_INIT_VALUE] = reg_addr;

    /* Please take the below API as your reference
     * for read the data using I2C communication
     * add your I2C read API here.
     * "BNO055_iERROR = I2C_WRITE_READ_STRING(DEV_ADDR,
     * ARRAY, ARRAY, 1, CNT)"
     * BNO055_iERROR is an return value of SPI write API
     * Please select your valid return value
     * In the driver BNO055_SUCCESS defined as 0
     * and FAILURE defined as -1
     */
    for (stringpos = BNO055_INIT_VALUE; stringpos < cnt; stringpos++)
        *(reg_data + stringpos) = array[stringpos];
    return (s8)BNO055_iERROR;
}

我的问题是，有没有人可以指导我通过这个挑战？我正在学习，https://www.kernel.org/doc/Documentation/i2c/dev-interface，但现在被困在这里了。为阅读/回复提前Thx。

Answer 1

我最近为MMA8451 i2c加速度计写了一个library similar to what you're describing。

本质上，Linux中的i2c控制器会被分配一个设备节点(例如/dev/i2c-1)。您将以文件like this形式打开此设备节点

int file = open(path, O_RDWR); //path = /dev/i2c-1

一旦有了文件句柄，就可以使用ioctl's读写i2c寄存器。i2c内核模块支持I2C_RDWR ioctl，它允许您与i2c寄存器交互。

要读取寄存器，您需要执行something like this

int mma8451_get_i2c_register(int file, unsigned char addr, unsigned char reg, unsigned char *val) {
    unsigned char inbuf, outbuf;
    struct i2c_rdwr_ioctl_data packets;
    struct i2c_msg messages[2];

    outbuf = reg;
    messages[0].addr  = addr;
    messages[0].flags = 0;
    messages[0].len   = sizeof(outbuf);
    messages[0].buf   = &outbuf;

    messages[1].addr  = addr;
    messages[1].flags = I2C_M_RD;
    messages[1].len   = sizeof(inbuf);
    messages[1].buf   = &inbuf;

    packets.msgs      = messages;
    packets.nmsgs     = 2;
    if(ioctl(file, I2C_RDWR, &packets) < 0) {
        return 0;
    }
    *val = inbuf;

    return 1;
}

要写入寄存器，您需要执行something like this

int mma8451_set_i2c_register(int file, unsigned char addr, unsigned char reg, unsigned char value) {
    unsigned char outbuf[2];
    struct i2c_rdwr_ioctl_data packets;
    struct i2c_msg messages[1];

    messages[0].addr  = addr;
    messages[0].flags = 0;
    messages[0].len   = sizeof(outbuf);
    messages[0].buf   = outbuf;

    outbuf[0] = reg;
    outbuf[1] = value;

    packets.msgs  = messages;
    packets.nmsgs = 1;
    if(ioctl(file, I2C_RDWR, &packets) < 0) {
        return 0;
    }

    return 1;
}

编辑：I2C_RDWR ioctl采用i2c_rdwr_ioctl_data结构作为参数。我是described like this

另一个常见的数据结构是struct i2c_rdwr_ioctl_data

这是在I2C_RDWR ioctl调用中使用的结构

struct i2c_rdwr_ioctl_data { struct i2c_msg __user *msgs; /* pointers to i2c_msgs */ __u32 nmsgs; /* number of i2c_msgs */ };

(在linux/i2c-dev.h中定义)这个结构指向要处理的i2c_msg数组，并定义数组中的i2c_msg数量。

用法:如果程序要写入一个字节(例如-索引字节)，然后读取一个字节，则需要两个结构i2c_msg数据结构。一个用于写入，另一个用于读取。这两个数据结构应该声明为两个i2c_msg数据结构的数组。它们将按照它们在数组中出现的顺序进行处理。

i2c_rdwr_ioctl_data结构包含一个指向i2c_msg结构数组的指针。这些结构包含您想要发送或接收的实际消息。例如，我的加速计为了读取一个寄存器，我首先需要将我想要读取的寄存器写入设备，然后我就可以读取它(这就是为什么在我的read函数中有两个i2c_msg)。

您需要参考data sheet for your BNO055来准确地找出哪些寄存器做了什么。

至于你的例子，它看起来来自bno055_support.c。看起来这只是你打算实现的一组存根。它看起来基本上是一个真实界面的模拟。所以重要的是接口，而不是实际的代码(所以不用担心cnt)。重要的部分如下：

s8 I2C_routine(void)
{
    bno055.bus_write = BNO055_I2C_bus_write;
    bno055.bus_read = BNO055_I2C_bus_read;
    bno055.delay_msec = BNO055_delay_msek;
    bno055.dev_addr = BNO055_I2C_ADDR1;

    return BNO055_INIT_VALUE;
}

这会将设备结构上的函数指针设置为将要定义的写入函数，并设置设备的地址和延迟。在此基础上，您需要实现与此接口匹配的函数：

#define BNO055_BUS_WRITE_FUNC(dev_addr, reg_addr, reg_data, wr_len)\
    bus_write(dev_addr, reg_addr, reg_data, wr_len)


#define BNO055_BUS_READ_FUNC(dev_addr, reg_addr, reg_data, r_len)\
    bus_read(dev_addr, reg_addr, reg_data, r_len)

我上面给你的函数应该是非常接近的。祝好运!

Answer 2

例如

s8 BNO055_I2C_bus_read(u8 dev_addr, u8 reg_addr, u8 *reg_data, u8 cnt)
{
    u8 array[I2C_BUFFER_LEN] = { BNO055_INIT_VALUE };
    array[BNO055_INIT_VALUE] = reg_addr;
    
    if (write(file, array, 1) != 1) {
        return -1;
    }
    std::this_thread::sleep_for(std::chrono::milliseconds(50));
    s8 res = read(file, reg_data, cnt);

    if (res > 0) return 0;
    else return -1;

}
s8 BNO055_I2C_bus_write(u8 dev_addr, u8 reg_addr, u8 *reg_data, u8 cnt)
{
    char buf[1 + cnt];
    buf[0] = reg_addr;
    memcpy(&buf[1], reg_data, cnt);

    if (write(file, buf, cnt+1) != cnt+1) {
        return -1;
    }
    return 0;
}