stm32专题十六：IIC（三）stm32 IIC 固件库函数分析

因为I2C通讯非常重要，因此要详细的分析每一个库函数

IIC初始化结构体

/** 
  * @brief  I2C Init structure definition  
  */

typedef struct
{
  // 指定时钟频率，这个值不能超过400kHz
  uint32_t I2C_ClockSpeed;          /*!< Specifies the clock frequency.
                                         This parameter must be set to a value lower than 400kHz */

  // IIC模式：可以有3种选择：I2C_Mode_I2C  I2C_Mode_SMBusDevice  I2C_Mode_SMBusHost
  uint16_t I2C_Mode;                /*!< Specifies the I2C mode.
                                         This parameter can be a value of @ref I2C_mode */

  
  // 占空比 I2C_DutyCycle_2  I2C_DutyCycle_16_9
  uint16_t I2C_DutyCycle;           /*!< Specifies the I2C fast mode duty cycle.
                                         This parameter can be a value of @ref I2C_duty_cycle_in_fast_mode */

  // 自身地址，这个可以任意给一个与其他IIC从机设备不同的地址，如0X0A
  uint16_t I2C_OwnAddress1;         /*!< Specifies the first device own address.
                                         This parameter can be a 7-bit or 10-bit address. */

  // 应答Ack使能 I2C_Ack_Enable  I2C_Ack_Disable
  uint16_t I2C_Ack;                 /*!< Enables or disables the acknowledgement.
                                         This parameter can be a value of @ref I2C_acknowledgement */

  // IIC应答地址，一般7位  I2C_AcknowledgedAddress_7bit  I2C_AcknowledgedAddress_10bit
  uint16_t I2C_AcknowledgedAddress; /*!< Specifies if 7-bit or 10-bit address is acknowledged.
                                         This parameter can be a value of @ref I2C_acknowledged_address */
}I2C_InitTypeDef;

IIC初始化函数，这里有一些值得注意的地方：

1 IIC模块时钟频率

2 分频系数

/**
  * @brief  Initializes the I2Cx peripheral according to the specified 
  *   parameters in the I2C_InitStruct.
  * @param  I2Cx: where x can be 1 or 2 to select the I2C peripheral.
  * @param  I2C_InitStruct: pointer to a I2C_InitTypeDef structure that
  *   contains the configuration information for the specified I2C peripheral.
  * @retval None
  */
void I2C_Init(I2C_TypeDef* I2Cx, I2C_InitTypeDef* I2C_InitStruct)
{
  uint16_t tmpreg = 0, freqrange = 0;
  uint16_t result = 0x04;
  uint32_t pclk1 = 8000000;  // 只是初始化时给的值，没有意义，给0也可以
  RCC_ClocksTypeDef  rcc_clocks;

/*---------------------------- I2Cx CR2 Configuration ------------------------*/
  // 配置IIC模块输入时钟频率，标准模式至少为2MHz，快速模式至少为4MHz，最大为36MHz
  /* Get the I2Cx CR2 value */
  // 先暂存CR2，只处理FREQ[5:0]位，其他位不变
  tmpreg = I2Cx->CR2;
  /* Clear frequency FREQ[5:0] bits */
  // 清除FREQ[5:0]位
  tmpreg &= CR2_FREQ_Reset;
  /* Get pclk1 frequency value */
  RCC_GetClocksFreq(&rcc_clocks);
  // 获得APB1总线的时钟频率（36MHz）
  pclk1 = rcc_clocks.PCLK1_Frequency;
  /* Set frequency bits depending on pclk1 value */
  // 计算FREQ[5:0]位写入值（36，已经是最大值）
  freqrange = (uint16_t)(pclk1 / 1000000);
  tmpreg |= freqrange;
  /* Write to I2Cx CR2 */
  // 写入到CR2寄存器
  I2Cx->CR2 = tmpreg;

/*---------------------------- I2Cx CCR Configuration ------------------------*/
  // 配置CCR寄存器（设置标准/快速模式、占空比、时钟控制分频系数等）
  /* Disable the selected I2C peripheral to configure TRISE */
  I2Cx->CR1 &= CR1_PE_Reset;
  /* Reset tmpreg value */
  /* Clear F/S, DUTY and CCR[11:0] bits */
  tmpreg = 0;

  /* Configure speed in standard mode */
  // I2C_ClockSpeed <= 100k时，配置为标准模式
  if (I2C_InitStruct->I2C_ClockSpeed <= 100000)
  {
    /* Standard mode speed calculate */
    // APB1总线时钟/2/I2C_ClockSpeed = 分频系数
    result = (uint16_t)(pclk1 / (I2C_InitStruct->I2C_ClockSpeed << 1));
    // 允许设定的最小值为0x04，在快速DUTY模式下允许的最小值为0x01；
    /* Test if CCR value is under 0x4*/
    if (result < 0x04)
    {
      /* Set minimum allowed value */
      result = 0x04;  
    }
    /* Set speed value for standard mode */
    tmpreg |= result;	  
    /* Set Maximum Rise Time for standard mode */
    I2Cx->TRISE = freqrange + 1; 
  }
  /* Configure speed in fast mode */
  // 快速模式下，分频系数的计算
  else /*(I2C_InitStruct->I2C_ClockSpeed <= 400000)*/
  {
    if (I2C_InitStruct->I2C_DutyCycle == I2C_DutyCycle_2)
    {
      /* Fast mode speed calculate: Tlow/Thigh = 2 */
      result = (uint16_t)(pclk1 / (I2C_InitStruct->I2C_ClockSpeed * 3));
    }
    else /*I2C_InitStruct->I2C_DutyCycle == I2C_DutyCycle_16_9*/
    {
      /* Fast mode speed calculate: Tlow/Thigh = 16/9 */
      result = (uint16_t)(pclk1 / (I2C_InitStruct->I2C_ClockSpeed * 25));
      /* Set DUTY bit */
      result |= I2C_DutyCycle_16_9;
    }

    /* Test if CCR value is under 0x1*/
    if ((result & CCR_CCR_Set) == 0)
    {
      /* Set minimum allowed value */
      result |= (uint16_t)0x0001;  
    }
    /* Set speed value and set F/S bit for fast mode */
    tmpreg |= (uint16_t)(result | CCR_FS_Set);
    /* Set Maximum Rise Time for fast mode */
    I2Cx->TRISE = (uint16_t)(((freqrange * (uint16_t)300) / (uint16_t)1000) + (uint16_t)1);  
  }

  /* Write to I2Cx CCR */
  // 写入到CCR寄存器，并使能IIC
  I2Cx->CCR = tmpreg;
  /* Enable the selected I2C peripheral */
  I2Cx->CR1 |= CR1_PE_Set;

/*---------------------------- I2Cx CR1 Configuration ------------------------*/
  // 配置IIC模式、应答
  /* Get the I2Cx CR1 value */
  tmpreg = I2Cx->CR1;
  /* Clear ACK, SMBTYPE and  SMBUS bits */
  tmpreg &= CR1_CLEAR_Mask;
  /* Configure I2Cx: mode and acknowledgement */
  /* Set SMBTYPE and SMBUS bits according to I2C_Mode value */
  /* Set ACK bit according to I2C_Ack value */
  tmpreg |= (uint16_t)((uint32_t)I2C_InitStruct->I2C_Mode | I2C_InitStruct->I2C_Ack);
  /* Write to I2Cx CR1 */
  I2Cx->CR1 = tmpreg;

/*---------------------------- I2Cx OAR1 Configuration -----------------------*/
  // 配置IIC应答地址位数
  /* Set I2Cx Own Address1 and acknowledged address */
  I2Cx->OAR1 = (I2C_InitStruct->I2C_AcknowledgedAddress | I2C_InitStruct->I2C_OwnAddress1);
}

在上一节中提到，IIC发送/接收过程会产生相应的事件，我们通过检测事件来判断当前运行的状态，以下是检测函数

ErrorStatus I2C_CheckEvent(I2C_TypeDef* I2Cx, uint32_t I2C_EVENT);

/**
  * @brief  Checks whether the last I2Cx Event is equal to the one passed
  *   as parameter.
  * @param  I2Cx: where x can be 1 or 2 to select the I2C peripheral.
  * @param  I2C_EVENT: specifies the event to be checked. 
  *   This parameter can be one of the following values:
  *     @arg I2C_EVENT_SLAVE_TRANSMITTER_ADDRESS_MATCHED           : EV1
  *     @arg I2C_EVENT_SLAVE_RECEIVER_ADDRESS_MATCHED              : EV1
  *     @arg I2C_EVENT_SLAVE_TRANSMITTER_SECONDADDRESS_MATCHED     : EV1
  *     @arg I2C_EVENT_SLAVE_RECEIVER_SECONDADDRESS_MATCHED        : EV1
  *     @arg I2C_EVENT_SLAVE_GENERALCALLADDRESS_MATCHED            : EV1
  *     @arg I2C_EVENT_SLAVE_BYTE_RECEIVED                         : EV2
  *     @arg (I2C_EVENT_SLAVE_BYTE_RECEIVED | I2C_FLAG_DUALF)      : EV2
  *     @arg (I2C_EVENT_SLAVE_BYTE_RECEIVED | I2C_FLAG_GENCALL)    : EV2
  *     @arg I2C_EVENT_SLAVE_BYTE_TRANSMITTED                      : EV3
  *     @arg (I2C_EVENT_SLAVE_BYTE_TRANSMITTED | I2C_FLAG_DUALF)   : EV3
  *     @arg (I2C_EVENT_SLAVE_BYTE_TRANSMITTED | I2C_FLAG_GENCALL) : EV3
  *     @arg I2C_EVENT_SLAVE_ACK_FAILURE                           : EV3_2
  *     @arg I2C_EVENT_SLAVE_STOP_DETECTED                         : EV4
  *     @arg I2C_EVENT_MASTER_MODE_SELECT                          : EV5
  *     @arg I2C_EVENT_MASTER_TRANSMITTER_MODE_SELECTED            : EV6     
  *     @arg I2C_EVENT_MASTER_RECEIVER_MODE_SELECTED               : EV6
  *     @arg I2C_EVENT_MASTER_BYTE_RECEIVED                        : EV7
  *     @arg I2C_EVENT_MASTER_BYTE_TRANSMITTING                    : EV8
  *     @arg I2C_EVENT_MASTER_BYTE_TRANSMITTED                     : EV8_2
  *     @arg I2C_EVENT_MASTER_MODE_ADDRESS10                       : EV9
  *     
  * @note: For detailed description of Events, please refer to section 
  *    I2C_Events in stm32f10x_i2c.h file.
  *    
  * @retval An ErrorStatus enumeration value:
  * - SUCCESS: Last event is equal to the I2C_EVENT
  * - ERROR: Last event is different from the I2C_EVENT
  */
ErrorStatus I2C_CheckEvent(I2C_TypeDef* I2Cx, uint32_t I2C_EVENT)
{
  uint32_t lastevent = 0;
  uint32_t flag1 = 0, flag2 = 0;
  ErrorStatus status = ERROR;

  /* Check the parameters */
  assert_param(IS_I2C_ALL_PERIPH(I2Cx));
  assert_param(IS_I2C_EVENT(I2C_EVENT));

  /* Read the I2Cx status register */
  // 分别读取SR1 SR2两个状态寄存器（16位），然后把状态合并到32位数据中
  flag1 = I2Cx->SR1;
  flag2 = I2Cx->SR2;
  flag2 = flag2 << 16;

  /* Get the last event value from I2C status register */
  
  lastevent = (flag1 | flag2) & FLAG_Mask;

  /* Check whether the last event contains the I2C_EVENT */
  if ((lastevent & I2C_EVENT) == I2C_EVENT)
  {
    // 判断事件是否正确发生
    /* SUCCESS: last event is equal to I2C_EVENT */
    status = SUCCESS;
  }
  else
  {
    /* ERROR: last event is different from I2C_EVENT */
    status = ERROR;
  }
  /* Return status */
  return status;
}

检测标志位的函数，其实也是读取SR1 SR2的相应位

FlagStatus I2C_GetFlagStatus(I2C_TypeDef* I2Cx, uint32_t I2C_FLAG);

/**
  * @brief  Checks whether the specified I2C flag is set or not.
  * @param  I2Cx: where x can be 1 or 2 to select the I2C peripheral.
  * @param  I2C_FLAG: specifies the flag to check. 
  *   This parameter can be one of the following values:
  *     @arg I2C_FLAG_DUALF: Dual flag (Slave mode)
  *     @arg I2C_FLAG_SMBHOST: SMBus host header (Slave mode)
  *     @arg I2C_FLAG_SMBDEFAULT: SMBus default header (Slave mode)
  *     @arg I2C_FLAG_GENCALL: General call header flag (Slave mode)
  *     @arg I2C_FLAG_TRA: Transmitter/Receiver flag
  *     @arg I2C_FLAG_BUSY: Bus busy flag
  *     @arg I2C_FLAG_MSL: Master/Slave flag
  *     @arg I2C_FLAG_SMBALERT: SMBus Alert flag
  *     @arg I2C_FLAG_TIMEOUT: Timeout or Tlow error flag
  *     @arg I2C_FLAG_PECERR: PEC error in reception flag
  *     @arg I2C_FLAG_OVR: Overrun/Underrun flag (Slave mode)
  *     @arg I2C_FLAG_AF: Acknowledge failure flag
  *     @arg I2C_FLAG_ARLO: Arbitration lost flag (Master mode)
  *     @arg I2C_FLAG_BERR: Bus error flag
  *     @arg I2C_FLAG_TXE: Data register empty flag (Transmitter)
  *     @arg I2C_FLAG_RXNE: Data register not empty (Receiver) flag
  *     @arg I2C_FLAG_STOPF: Stop detection flag (Slave mode)
  *     @arg I2C_FLAG_ADD10: 10-bit header sent flag (Master mode)
  *     @arg I2C_FLAG_BTF: Byte transfer finished flag
  *     @arg I2C_FLAG_ADDR: Address sent flag (Master mode) "ADSL"
  *   Address matched flag (Slave mode)"ENDA"
  *     @arg I2C_FLAG_SB: Start bit flag (Master mode)
  * @retval The new state of I2C_FLAG (SET or RESET).
  */
FlagStatus I2C_GetFlagStatus(I2C_TypeDef* I2Cx, uint32_t I2C_FLAG)
{
  FlagStatus bitstatus = RESET;
  __IO uint32_t i2creg = 0, i2cxbase = 0;

  /* Check the parameters */
  assert_param(IS_I2C_ALL_PERIPH(I2Cx));
  assert_param(IS_I2C_GET_FLAG(I2C_FLAG));

  /* Get the I2Cx peripheral base address */
  i2cxbase = (uint32_t)I2Cx;
  
  /* Read flag register index */
  i2creg = I2C_FLAG >> 28;
  
  /* Get bit[23:0] of the flag */
  I2C_FLAG &= FLAG_Mask;
  
  if(i2creg != 0)
  {
    /* Get the I2Cx SR1 register address */
    i2cxbase += 0x14;
  }
  else
  {
    /* Flag in I2Cx SR2 Register */
    I2C_FLAG = (uint32_t)(I2C_FLAG >> 16);
    /* Get the I2Cx SR2 register address */
    i2cxbase += 0x18;
  }
  
  if(((*(__IO uint32_t *)i2cxbase) & I2C_FLAG) != (uint32_t)RESET)
  {
    /* I2C_FLAG is set */
    bitstatus = SET;
  }
  else
  {
    /* I2C_FLAG is reset */
    bitstatus = RESET;
  }
  
  /* Return the I2C_FLAG status */
  return  bitstatus;
}

发送7位地址的函数（这里就有一个问题，到底是7位还是8位），可以直接看源码。从源码中可以很清楚的看到，我们需要提供的就是8位地址，而且不论是读地址或者是写地址都可以，该函数会自动修改最后一位。

void I2C_Send7bitAddress(I2C_TypeDef* I2Cx, uint8_t Address, uint8_t I2C_Direction);

/**
  * @brief  Transmits the address byte to select the slave device.
  * @param  I2Cx: where x can be 1 or 2 to select the I2C peripheral.
  * @param  Address: specifies the slave address which will be transmitted
  * @param  I2C_Direction: specifies whether the I2C device will be a
  *   Transmitter or a Receiver. This parameter can be one of the following values
  *     @arg I2C_Direction_Transmitter: Transmitter mode
  *     @arg I2C_Direction_Receiver: Receiver mode
  * @retval None.
  */
void I2C_Send7bitAddress(I2C_TypeDef* I2Cx, uint8_t Address, uint8_t I2C_Direction)
{
  /* Check the parameters */
  assert_param(IS_I2C_ALL_PERIPH(I2Cx));
  assert_param(IS_I2C_DIRECTION(I2C_Direction));
  /* Test on the direction to set/reset the read/write bit */
  // 如果是写方向
  if (I2C_Direction != I2C_Direction_Transmitter)
  {
    /* Set the address bit0 for read */
    // 把最后一位置0，这里可以看到，我们实际上需要提供的是8位地址
    Address |= OAR1_ADD0_Set;
  }
  // 如果是读方向，最后一位清0
  else
  {
    /* Reset the address bit0 for write */
    Address &= OAR1_ADD0_Reset;
  }
  // 然后把数据写入到DR寄存器
  /* Send the address */
  I2Cx->DR = Address;
}

发送数据函数（直接把数据写入到DR寄存器）

void I2C_SendData(I2C_TypeDef* I2Cx, uint8_t Data)
{
  /* Check the parameters */
  assert_param(IS_I2C_ALL_PERIPH(I2Cx));
  /* Write in the DR register the data to be sent */
  I2Cx->DR = Data;
}

接收数据函数（返回DR寄存器的值）

uint8_t I2C_ReceiveData(I2C_TypeDef* I2Cx)
{
  /* Check the parameters */
  assert_param(IS_I2C_ALL_PERIPH(I2Cx));
  /* Return the data in the DR register */
  return (uint8_t)I2Cx->DR;
}