Quick Start Guide for SERCOM I2C Slave - Callback

In this use case, the I²C will used and set up as follows:

• Slave mode
• 100KHz operation speed
• Not operational in standby
• 10000 packet timeout value

Prerequisites

The device must be connected to an I²C master.

Setup

Code

The following must be added to the user application:

A sample buffer to write from, a sample buffer to read to and length of buffers:

#define DATA_LENGTH 10
static uint8_t write_buffer[DATA_LENGTH] = {
        0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09,
};
static uint8_t read_buffer [DATA_LENGTH];

Address to respond to:

#define SLAVE_ADDRESS 0x12

Globally accessible module structure:

struct i2c_slave_module i2c_slave_instance;

Globally accessible packet:

static struct i2c_slave_packet packet;

Function for setting up the module:

void configure_i2c_slave(void)
{
    /* Initialize config structure and module instance */
    struct i2c_slave_config config_i2c_slave;
    i2c_slave_get_config_defaults(&config_i2c_slave);
    /* Change address and address_mode */
    config_i2c_slave.address      = SLAVE_ADDRESS;
    config_i2c_slave.address_mode = I2C_SLAVE_ADDRESS_MODE_MASK;
#if SAMR30  
    config_i2c_slave.pinmux_pad0    = CONF_SLAVE_SDA_PINMUX;
    config_i2c_slave.pinmux_pad1    = CONF_SLAVE_SCK_PINMUX;
#endif
    /* Initialize and enable device with config */
    i2c_slave_init(&i2c_slave_instance, CONF_I2C_SLAVE_MODULE, &config_i2c_slave);

    i2c_slave_enable(&i2c_slave_instance);
}

Callback function for read request from a master:

void i2c_read_request_callback(
        struct i2c_slave_module *const module)
{
    /* Init i2c packet */
    packet.data_length = DATA_LENGTH;
    packet.data        = write_buffer;

    /* Write buffer to master */
    i2c_slave_write_packet_job(module, &packet);
}

Callback function for write request from a master:

void i2c_write_request_callback(
        struct i2c_slave_module *const module)
{
    /* Init i2c packet */
    packet.data_length = DATA_LENGTH;
    packet.data        = read_buffer;

    /* Read buffer from master */
    if (i2c_slave_read_packet_job(module, &packet) != STATUS_OK) {
    }
}

Function for setting up the callback functionality of the driver:

void configure_i2c_slave_callbacks(void)
{
    /* Register and enable callback functions */
    i2c_slave_register_callback(&i2c_slave_instance, i2c_read_request_callback,
            I2C_SLAVE_CALLBACK_READ_REQUEST);
    i2c_slave_enable_callback(&i2c_slave_instance,
            I2C_SLAVE_CALLBACK_READ_REQUEST);

    i2c_slave_register_callback(&i2c_slave_instance, i2c_write_request_callback,
            I2C_SLAVE_CALLBACK_WRITE_REQUEST);
    i2c_slave_enable_callback(&i2c_slave_instance,
            I2C_SLAVE_CALLBACK_WRITE_REQUEST);
}

Add to user application main():

    /* Configure device and enable */
    configure_i2c_slave();
    configure_i2c_slave_callbacks();

Workflow

1. Configure and enable module.

       configure_i2c_slave();

   1. Create and initialize configuration structure.

          struct i2c_slave_config config_i2c_slave;
          i2c_slave_get_config_defaults(&config_i2c_slave);

   2. Change address and address mode settings in the configuration.

          config_i2c_slave.address      = SLAVE_ADDRESS;
          config_i2c_slave.address_mode = I2C_SLAVE_ADDRESS_MODE_MASK;
      #if SAMR30  
          config_i2c_slave.pinmux_pad0    = CONF_SLAVE_SDA_PINMUX;
          config_i2c_slave.pinmux_pad1    = CONF_SLAVE_SCK_PINMUX;
      #endif

   3. Initialize the module with the set configurations.

          i2c_slave_init(&i2c_slave_instance, CONF_I2C_SLAVE_MODULE, &config_i2c_slave);

   4. Enable the module.

          i2c_slave_enable(&i2c_slave_instance);

2. Register and enable callback functions.

       configure_i2c_slave_callbacks();

   1. Register and enable callbacks for read and write requests from master.

          i2c_slave_register_callback(&i2c_slave_instance, i2c_read_request_callback,
                  I2C_SLAVE_CALLBACK_READ_REQUEST);
          i2c_slave_enable_callback(&i2c_slave_instance,
                  I2C_SLAVE_CALLBACK_READ_REQUEST);
      
          i2c_slave_register_callback(&i2c_slave_instance, i2c_write_request_callback,
                  I2C_SLAVE_CALLBACK_WRITE_REQUEST);
          i2c_slave_enable_callback(&i2c_slave_instance,
                  I2C_SLAVE_CALLBACK_WRITE_REQUEST);

Implementation

Code

Add to user application main():

    while (true) {
        /* Infinite loop while waiting for I2C master interaction */
    }

Workflow

1. Infinite while loop, while waiting for interaction from master.

       while (true) {
           /* Infinite loop while waiting for I2C master interaction */
       }

Callback

When an address packet is received, one of the callback functions will be called, depending on the DIR bit in the received packet.

Workflow

• Read request callback:
  1. Length of buffer and buffer to be sent to master is initialized.

         packet.data_length = DATA_LENGTH;
         packet.data        = write_buffer;

  2. Write packet to master.

         i2c_slave_write_packet_job(module, &packet);

• Write request callback:
  1. Length of buffer and buffer to be read from master is initialized.

         packet.data_length = DATA_LENGTH;
         packet.data        = read_buffer;

  2. Read packet from master.

         if (i2c_slave_read_packet_job(module, &packet) != STATUS_OK) {
         }