Workflow

Select slave.

spi_select_slave(&spi_master_instance, &slave, true);

Write buffer to SPI slave.

spi_transceive_buffer_job(&spi_master_instance, wr_buffer,rd_buffer,BUF_LENGTH);

Wait for the transfer to be complete.

while (!transrev_complete_spi_master) {
}
transrev_complete_spi_master = false;

Deselect slave.

spi_select_slave(&spi_master_instance, &slave, false);

Infinite loop.

while (true) {
    /* Infinite loop */
    if (!port_pin_get_input_level(BUTTON_0_PIN)) {
        spi_select_slave(&spi_master_instance, &slave, true);
        spi_transceive_buffer_job(&spi_master_instance, wr_buffer,rd_buffer,BUF_LENGTH);
        while (!transrev_complete_spi_master) {
        }
        transrev_complete_spi_master = false;
        spi_select_slave(&spi_master_instance, &slave, false);
    }
}