Quick Start Guide for SERCOM SPI Master - Polled

In this use case, the SPI on extension header 1 of the Xplained Pro board will be configured with the following settings:

• Master Mode enabled
• MSB of the data is transmitted first
• Transfer mode 0
• SPI MUX Setting E (see Master Mode Settings)
• 8-bit character size
• Not enabled in sleep mode
• Baudrate 100000
• GLCK generator 0

Setup

Prerequisites

There are no special setup requirements for this use-case.

Code

The following must be added to the user application:

A sample buffer to send via SPI.

static uint8_t buffer[BUF_LENGTH] = {
        0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09,
        0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10, 0x11, 0x12, 0x13
};

Number of entries in the sample buffer.

#define BUF_LENGTH 20

GPIO pin to use as Slave Select.

#define SLAVE_SELECT_PIN CONF_MASTER_SS_PIN

A globally available software device instance struct to store the SPI driver state while it is in use.

struct spi_module spi_master_instance;

A globally available peripheral slave software device instance struct.

struct spi_slave_inst slave;

A function for configuring the SPI.

void configure_spi_master(void)
{
    struct spi_config config_spi_master;
    struct spi_slave_inst_config slave_dev_config;
    /* Configure and initialize software device instance of peripheral slave */
    spi_slave_inst_get_config_defaults(&slave_dev_config);
    slave_dev_config.ss_pin = SLAVE_SELECT_PIN;
    spi_attach_slave(&slave, &slave_dev_config);
    /* Configure, initialize and enable SERCOM SPI module */
    spi_get_config_defaults(&config_spi_master);
    config_spi_master.mux_setting = CONF_MASTER_MUX_SETTING;
    config_spi_master.pinmux_pad0 = CONF_MASTER_PINMUX_PAD0;
    config_spi_master.pinmux_pad1 = CONF_MASTER_PINMUX_PAD1;
    config_spi_master.pinmux_pad2 = CONF_MASTER_PINMUX_PAD2;
    config_spi_master.pinmux_pad3 = CONF_MASTER_PINMUX_PAD3;

    spi_init(&spi_master_instance, CONF_MASTER_SPI_MODULE, &config_spi_master);

    spi_enable(&spi_master_instance);

}

Add to user application main().

    system_init();
    configure_spi_master();

Workflow

1. Initialize system.

       system_init();

2. Set-up the SPI.

       configure_spi_master();

   1. Create configuration struct.

          struct spi_config config_spi_master;

   2. Create peripheral slave configuration struct.

          struct spi_slave_inst_config slave_dev_config;

   3. Create peripheral slave software device instance struct.

      struct spi_slave_inst slave;

   4. Get default peripheral slave configuration.

          spi_slave_inst_get_config_defaults(&slave_dev_config);

   5. Set Slave Select pin.

          slave_dev_config.ss_pin = SLAVE_SELECT_PIN;

   6. Initialize peripheral slave software instance with configuration.

          spi_attach_slave(&slave, &slave_dev_config);

   7. Get default configuration to edit.

          spi_get_config_defaults(&config_spi_master);

   8. Set MUX setting E.

          config_spi_master.mux_setting = CONF_MASTER_MUX_SETTING;

   9. Set pinmux for pad 0 (data in (MISO)).
   10. Set pinmux for pad 1 as unused, so the pin can be used for other purposes.
   11. Set pinmux for pad 2 (data out (MOSI)).
   12. Set pinmux for pad 3 (SCK).
   13. Initialize SPI module with configuration.

           spi_init(&spi_master_instance, CONF_MASTER_SPI_MODULE, &config_spi_master);

   14. Enable SPI module.

           spi_enable(&spi_master_instance);

Use Case

Code

Add the following to your user application main().

    while (true) {
        /* Infinite loop */
        if(!port_pin_get_input_level(BUTTON_0_PIN)) {
            spi_select_slave(&spi_master_instance, &slave, true);
            spi_write_buffer_wait(&spi_master_instance, buffer, BUF_LENGTH);
            spi_select_slave(&spi_master_instance, &slave, false);
            port_pin_set_output_level(LED_0_PIN, LED0_ACTIVE);
        }
    }

Workflow

1. Select slave.

               spi_select_slave(&spi_master_instance, &slave, true);

2. Write buffer to SPI slave.

               spi_write_buffer_wait(&spi_master_instance, buffer, BUF_LENGTH);

3. Deselect slave.

               spi_select_slave(&spi_master_instance, &slave, false);

4. Light up.

               port_pin_set_output_level(LED_0_PIN, LED0_ACTIVE);

5. Infinite loop.

       while (true) {
           /* Infinite loop */
           if(!port_pin_get_input_level(BUTTON_0_PIN)) {
               spi_select_slave(&spi_master_instance, &slave, true);
               spi_write_buffer_wait(&spi_master_instance, buffer, BUF_LENGTH);
               spi_select_slave(&spi_master_instance, &slave, false);
               port_pin_set_output_level(LED_0_PIN, LED0_ACTIVE);
           }
       }