Workflow

Select slave.

spi_select_slave(&spi_master_instance, &slave, true);

Write buffer to SPI slave.

spi_write_buffer_wait(&spi_master_instance, buffer, BUF_LENGTH);

Deselect slave.

spi_select_slave(&spi_master_instance, &slave, false);

Light up.

port_pin_set_output_level(LED_0_PIN, LED0_ACTIVE);

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);
    }
}