quadrature_decoding.c

// Maps current state (index) to next state for a forward transition.
const int8 quadrature_states[] = {0x1, 0x3, 0x0, 0x2};

CY_ISR(quadrature_event_isr) {
	static int8 last_levels = 3;
	static int8 count = 0;
	
	int levels = Quadrature_Read();
	Quadrature_ClearInterrupt();

	if(quadrature_states[last_levels] == levels) {
		count += 1;
		last_levels = levels;
	} else if(quadrature_states[levels] == last_levels) {
		count -= 1;
		last_levels = levels;
	}
	
	if(abs(count) >= 4) {
		ui_event event = {.type = UI_EVENT_UPDOWN, .when = xTaskGetTickCountFromISR(), .int_arg = count / 4};
		xQueueSendToBackFromISR(ui_queue, &event, NULL);
		count = count % 4;
	}
}