一文解析RT-thread系统中IIC总线的设备驱动

本文主要介绍RT-thread中IIC总线设备驱动，涉及到的主要文件有：驱动框架文件（i2c_core.c，i2c_dev.c，i2c-bit-ops.c，i2c_dev.h，i2c.h）；底层硬件驱动文件（i2c_soft.c，i2c_soft.h）。这里的i2c_soft.c和i2c_soft.h是指利用MCU的GPIO口模拟IIC总线时序，而不是利用MCU的硬件IIC接口。应用IIC总线设备驱动时，需要在rtconfig.h中添加宏定义#define RT_USING_I2C。若使用GPIO口模拟IIC总线，则还需要添加宏定义#define RT_USING_I2C_BITOPS。

一、IIC总线设备驱动框架

先看i2c.h中定义的一些数据结构：

#define RT_I2C_WR 0x0000

#define RT_I2C_RD (1u << 0)

#define RT_I2C_ADDR_10BIT (1u << 2) /* this is a ten bit chip address */

#define RT_I2C_NO_START (1u << 4)

#define RT_I2C_IGNORE_NACK (1u << 5)

#define RT_I2C_NO_READ_ACK (1u << 6) /* when I2C reading, we do not ACK */

struct rt_i2c_msg

{

rt_uint16_t addr;

rt_uint16_t flags;

rt_uint16_t len;

rt_uint8_t  *buf;

};

struct rt_i2c_bus_device;

struct rt_i2c_bus_device_ops

{

rt_size_t (*master_xfer)(struct rt_i2c_bus_device *bus,

struct rt_i2c_msg msgs[],

                     rt_uint32_t num);

rt_size_t (*slave_xfer)(struct rt_i2c_bus_device *bus,

struct rt_i2c_msg msgs[],

                    rt_uint32_t num);

rt_err_t (*i2c_bus_control)(struct rt_i2c_bus_device *bus,

rt_uint32_t,

rt_uint32_t);

};

/for i2c bus driver/

struct rt_i2c_bus_device

{

struct rt_device parent;

const struct rt_i2c_bus_device_ops *ops;

rt_uint16_t flags;

rt_uint16_t addr;

struct rt_mutex lock;

rt_uint32_t timeout;

rt_uint32_t retries;

void *priv;

};

i2c_dev.h中相关数据结构（struct rt_i2c_priv_data用于i2c_bus_device_control()函数中RT_I2C_DEV_CTRL_RW控制标志）：

#define RT_I2C_DEV_CTRL_10BIT 0x20

#define RT_I2C_DEV_CTRL_ADDR 0x21

#define RT_I2C_DEV_CTRL_TIMEOUT 0x22

#define RT_I2C_DEV_CTRL_RW 0x23

struct rt_i2c_priv_data

{

struct rt_i2c_msg  *msgs;

rt_size_t  number;

};

i2c-bit-ops.h中主要定义了模拟IIC总线时序时需要的数据结构：

struct rt_i2c_bit_ops

{

void *data;            /* private data for lowlevel routines */

void (*set_sda)(void *data, rt_int32_t state);

void (*set_scl)(void *data, rt_int32_t state);

rt_int32_t (*get_sda)(void *data);

rt_int32_t (*get_scl)(void *data);



void (*udelay)(rt_uint32_t us);



rt_uint32_t delay_us;  /* scl and sda line delay */

rt_uint32_t timeout;   /* in tick */

};

在i2c_dev.c主要实现IIC设备驱动统一接口函数：i2c_bus_device_read()，i2c_bus_device_write()，i2c_bus_device_control()以及rt_i2c_bus_device_device_init()。

rt_err_t rt_i2c_bus_device_device_init(struct rt_i2c_bus_device *bus,

const char               *name)

{

struct rt_device *device;

RT_ASSERT(bus != RT_NULL);



device = &bus->parent;



device->user_data = bus;



/* set device type */

device->type    = RT_Device_Class_I2CBUS;

/* initialize device interface */

device->init    = RT_NULL;

device->open    = RT_NULL;

device->close   = RT_NULL;

device->read    = i2c_bus_device_read;

device->write   = i2c_bus_device_write;

device->control = i2c_bus_device_control;



/* register to device manager */

rt_device_register(device, name, RT_DEVICE_FLAG_RDWR);



return RT_EOK;

}

i2c_core.c中实现IIC总线设备注册，以及使用IIC总线进行数据传输，如：rt_i2c_transfer()，rt_i2c_master_send()，rt_i2c_master_recv()。

rt_err_t rt_i2c_bus_device_register(struct rt_i2c_bus_device *bus,

const char               *bus_name)

{

rt_err_t res = RT_EOK;



rt_mutex_init(&bus->lock, "i2c_bus_lock", RT_IPC_FLAG_FIFO);



if (bus->timeout == 0) bus->timeout = RT_TICK_PER_SECOND;



res = rt_i2c_bus_device_device_init(bus, bus_name);



i2c_dbg("I2C bus [%s] registered\n", bus_name);



return res;

}

i2c-bit-ops.c中主要实现了利用GPIO模拟IIC总线时序的相关接口函数，如：i2c_start()，i2c_restart()，i2c_stop()，i2c_waitack()，i2c_writeb()，i2c_readb()，i2c_send_bytes()，i2c_send_ack_or_nack()，i2c_recv_bytes()，i2c_send_address()，i2c_bit_send_address()等。并且实现了i2c_bit_xfer()：

static const struct rt_i2c_bus_device_ops i2c_bit_bus_ops =

{

i2c_bit_xfer,

RT_NULL,

RT_NULL

};

rt_err_t rt_i2c_bit_add_bus(struct rt_i2c_bus_device *bus,

const char               *bus_name)

{

bus->ops = &i2c_bit_bus_ops;



return rt_i2c_bus_device_register(bus, bus_name);

}

二、底层硬件驱动

本文采用的是模拟IIC，即用GPIO口模拟IIC时序。在i2c_soft.c中主要实现struct rt_i2c_bit_ops中的指针函数：

void stm32_set_sda(void *data, rt_int32_t state)

{

if(state == 1)

    GPIO_SetBits(I2C1_GPIO , I2C1_GPIO_SDA);   //GPIOB->BSRRL = I2C1_GPIO_SDA

else if(state == 0)

    GPIO_ResetBits(I2C1_GPIO , I2C1_GPIO_SDA); //GPIOB->BSRRH = I2C1_GPIO_SDA

}

void stm32_set_scl(void *data, rt_int32_t state)

{

if(state == 1)

    GPIO_SetBits(I2C1_GPIO , I2C1_GPIO_SCL);   //GPIOB->BSRRL = I2C1_GPIO_SCL

else if(state == 0)

    GPIO_ResetBits(I2C1_GPIO , I2C1_GPIO_SCL); //GPIOB->BSRRH = I2C1_GPIO_SCL

}

rt_int32_t stm32_get_sda(void *data)

{

return (rt_int32_t)GPIO_ReadInputDataBit(I2C1_GPIO , I2C1_GPIO_SDA);//return(GPIOB->IDR  & I2C1_GPIO_SDA)

}

rt_int32_t stm32_get_scl(void *data)

{

return (rt_int32_t)GPIO_ReadInputDataBit(I2C1_GPIO , I2C1_GPIO_SCL);//return(GPIOB->IDR  & I2C1_GPIO_SCL)

}

void stm32_udelay(rt_uint32_t us)

{

rt_uint32_t delta;

/* ¼ÆËãusÑÓʱËùÐè¼ÆÊýÖµ£»sysTick->LOAD=21000, RT_TICK_PER_SECOND=1000 */

us = us * (SysTick->LOAD/(1000000/RT_TICK_PER_SECOND));

/* »ñÈ¡µ±Ç°àÖ઼ÆÊýÖµ */

delta = SysTick->VAL;

/* ÑÓʱus */

while (delta - SysTick->VAL< us);

}

void stm32_mdelay(rt_uint32_t ms)

{

stm32_udelay(ms * 1000);

}

static const struct rt_i2c_bit_ops stm32_i2c_bit_ops =

{

(void*)0xaa,     //no use in set_sda,set_scl,get_sda,get_scl

stm32_set_sda,

stm32_set_scl,

stm32_get_sda,

stm32_get_scl,

stm32_udelay,

20, 

5

};

最后，实现IIC总线硬件初始化（包括RCC时钟配置和GPIO配置，最重要的是将stm32_i2c_bit_ops初始化为IIC总线设备结构体的priv变量，即stm32_i2c.priv = (void *)&stm32_i2c_bit_ops）：

int rt_hw_i2c_init(void)

{

static struct rt_i2c_bus_device stm32_i2c;//"static" add by me. It must be add "static", or it will be hard fault



RCC_Configuration();

GPIO_Configuration();



rt_memset((void *)&stm32_i2c, 0, sizeof(struct rt_i2c_bus_device));

stm32_i2c.priv = (void *)&stm32_i2c_bit_ops;

rt_i2c_bit_add_bus(&stm32_i2c, "i2c1");   

    

return 0;

}

INIT_BOARD_EXPORT(rt_hw_i2c_init);//rt_hw_i2c_init will be called in rt_components_board_init()

三、IIC总线设备初始化

这里以cs43l22数字音频放大器为例：

static rt_err_t cs43l22_init(const char * i2c_bus_name)

{

i2c_bus = (struct rt_i2c_bus_device *)rt_device_find(i2c_bus_name);

if(i2c_bus == RT_NULL)

{    

 rt_kprintf("\ni2c_bus %s for cs43l22 not found!\n", i2c_bus_name);

 return -RT_ENOSYS;

}

/* oflag has no meaning for spi device , so set to RT_NULL */

if(rt_device_open(&i2c_bus->parent, RT_NULL) != RT_EOK)

{

     rt_kprintf("\ni2c_bus %s for cs43l22 opened failed!\n", i2c_bus_name);

     return -RT_EEMPTY;

}



EVAL_AUDIO_Init(OUTPUT_DEVICE_AUTO, volume, I2S_AudioFreq_48k); 



/* it must be at the back of EVAL_AUDIO_Init, which reset the cs43l22 */

uint8_t chip_id = Codec_ReadRegister(i2c_bus, 0x01);

rt_kprintf("(chip_id of cs43l22 is 0x%02x)", chip_id);



return 0;

}

int rt_cs43l22_init(void)

{

rt_sem_init(&sem_cs43l22, "cs43l22", 1, RT_IPC_FLAG_FIFO);



cs43l22_init("i2c1");



return 0;

}

INIT_APP_EXPORT(rt_cs43l22_init);

注意事项：

1、在应用IIC总线设备驱动时，需要用到rt_device_read或rt_device_write，因此在初始化函数中需要调用rt_device_open将IIC总线设备打开。

2、下面利用rt_device_read和rt_device_write操作寄存器（每一次调用rt_device_read或rt_device_write都包括了i2c_start，i2c_bit_send_address，i2c_recv_bytes/i2c_send_bytes，i2c_stop这4个步骤）：

static uint32_t Codec_WriteRegister(struct rt_i2c_bus_device * i2c_bus, uint8_t RegisterAddr, uint8_t RegisterValue)

{

uint32_t result = 0;

rt_uint16_t flags = 0x00;

rt_uint16_t DevAddr = (rt_uint16_t)CODEC_ADDRESS >> 1;

rt_off_t pos = (rt_off_t)((flags << 16) | DevAddr);

rt_uint8_t buffer[2];

buffer[0] = RegisterAddr;

buffer[1] = RegisterValue;

rt_device_write(&i2c_bus->parent, pos, buffer, sizeof(buffer));

#ifdef VERIFY_WRITTENDATA

/* Verify that the data has been correctly written */

result = (Codec_ReadRegister(i2c_bus, RegisterAddr) == RegisterValue)? 0:1;

if(result == 0)

    rt_kprintf("\nthe reg 0x%02x verify passed\n",RegisterAddr);

else

    rt_kprintf("\nthe reg 0x%02x verify failed\n",RegisterAddr);

#endif /* VERIFY_WRITTENDATA */

/* Return the verifying value: 0 (Passed) or 1 (Failed) */

return result;

}

static uint8_t Codec_ReadRegister(struct rt_i2c_bus_device * i2c_bus, uint8_t RegisterAddr)

{

rt_uint16_t flags = 0x00;

rt_uint16_t DevAddr = (rt_uint16_t)CODEC_ADDRESS >> 1;

rt_off_t pos = (rt_off_t)((flags << 16) | DevAddr);

rt_uint8_t buffer;

buffer = RegisterAddr;

rt_device_write(&i2c_bus->parent, pos, &buffer, 1);

rt_device_read(&i2c_bus->parent, pos, &buffer, 1);

/* Return the byte read from Codec */

return buffer;

}

在上面两个函数中，有符号整型32位pos的高16位表示flags，低16位表示IIC器件地址。flags取值如i2c.h文件中宏定义所示。

这里说明一个问题：在rt_i2c_master_send和rt_i2c_master_recv函数中均有“msg.flags = flags & RT_I2C_ADDR_10BIT;”这一语句，该句用于标志IIC器件地址是否为10位地址，但是这条语句会将其他预置好的标志全部清除，如RT_I2C_NO_START，RT_I2C_IGNORE_NACK或RT_I2C_NO_READ_ACK。所以，在一般情况下，flags标志只能事先预置RT_I2C_ADDR_10BIT，若IIC器件地址为7位，则直接设置flags为0。

3、根据i2c_bit_send_address()函数中：

else

{

/* 7-bit addr */

addr1 = msg->addr << 1;

if (flags & RT_I2C_RD)

    addr1 |= 1;

ret = i2c_send_address(bus, addr1, retries);

if ((ret != 1) && !ignore_nack)

    return -RT_EIO;

}

可得，若IIC器件地址为7位，则pos低16位所表示的地址值DevAddr不包括读写标志位（最低位）。而cs43l22数据手册中的8位地址值包含了读写标志位，因此设置DevAddr为CODEC_ADDRESS >> 1。

原作者：King先生