static enum hrtimer_restart spike_timer_callback(struct hrtimer *timer)
{
	if (!spike_dev.running) {
		return HRTIMER_NORESTART;
	}

	/* busy means the previous message has not completed */
	if (spike_ctl.busy) {
		spike_ctl.busy_counter++;
	}
	else if (spike_queue_spi_write() != 0) {
		return HRTIMER_NORESTART;
	}

	hrtimer_forward_now(&spike_dev.timer,
		ktime_set(spike_dev.timer_period_sec,
			spike_dev.timer_period_ns));

	return HRTIMER_RESTART;
}