I2C Device Drivers

  • include/nuttx/i2c/i2c_master.h All structures and APIs needed to work with I2C drivers are provided in this header file.

  • struct i2c_ops_s. Each I2C device driver must implement an instance of struct i2c_ops_s. That structure defines a call table with the following methods:

  • Binding I2C Drivers. I2C drivers are not normally directly accessed by user code, but are usually bound to another, higher level device driver. In general, the binding sequence is:

    1. Get an instance of struct i2c_master_s from the hardware-specific I2C device driver, and

    2. Provide that instance to the initialization method of the higher level device driver.

  • Examples: arch/z80/src/ez80/ez80_i2c.c, arch/z80/src/z8/z8_i2c.c, etc.

I2C Slave Device Drivers

  • include/nuttx/i2c/i2c_slave.h Declaration of all macros and ops and int i2c_slave_register, used to bind the lowerhalf driver to the upper one and register an I2C slave device.

  • Binding I2C Slave Drivers. Use int i2c_slave_register in your BSP to register your slave device. Before that, you need to get the instance of struct i2c_slave_s from the hardware-specific I2C Slave driver.

  • Using I2C Slave in your Application. I2C slave drivers are normally directly accessed by user code, We can read and write to device nodes using posix interfaces. The device is registered as /dev/i2cslv%d, where %d is a number provided in the BSP initialization phase.

  • BSP initialization example (STM32 I2C Slave):

int stm32_i2cs_setup(void)
{
   i2cs = stm32_i2cbus_slaveinitialize(1);
   if (i2cs != NULL)
     {
       return -ENOENT;
     }
   return i2c_slave_register(i2cs, 1, 0x01, 7);
}

I2C Slave Driver API

int i2c_slave_register(FAR struct i2c_slave_s *dev, int bus, int addr, int nbit);

Bind the lowerhalf dev driver to the upperhalf driver and register a device. The name of the device is /dev/i2cslv%d, where %d is bus. The address the I2C slave is specified in addr. nbit is either 7 or 10 and it specifies the address format.

  • struct i2c_slaveops_s. Each I2C slave lowerhalf driver must implement an instance of struct i2c_slaveops_s. That structure defines a call table with the following methods:

    • setownaddress: the address the slave responds to,

    • write: sets the tx buffer pointer,

    • read: sets the rx buffer pointer,

    • registercallback: registers the callback function which should be called from a service routine. Signals the received or fully transferred I2C packet.

    • setup: initializes the peripheral,

    • shutdown: shutdowns the peripheral.