#include <nic.h>

__USING_SYS

#define N 4
#define T 300
#define K 0
#define RESYNCH_THRESH 20

typedef struct PDU {
	unsigned short ib[N];
	unsigned short ialvo;
};

PDU* pdu_sent;
PDU* pdu_rcvd;

int round = N * T;

int prev;
int timer;
int src;

void get_src() {
	for (int i = 0; i < N; i++)
		if (pdu_rcvd->ib[i] == 0xFFFF) {
			src = i;
			return;
		}
}

void receive() {
	int rssi;
	nic.receive(..., received, &rssi, &timer);
	get_src();
	if (src >= 0)
		pdu_sent->ib[src] = rssi;
	else {
		pdu_sent->ialvo = rssi;
		led_alvo_on();
	}
}

void send() {
	nic.send(..., pdu_sent);
	led_alvo_off();
	led_send_turn(); 
}

int main() {
	pdu_sent = (PDU*) malloc(sizeof(PDU));
	pdu_sent->ib[K] = 0xFFFF;
	pdu_rcvd = (PDU*) malloc(sizeof(PDU));
	
	prev = K - 1;
	if (prev < 0)                   // set the previous beacon
		prev += N;
	
	if (K > 0) {
		synch();                // wait for the previous beacon to send
		timer = T;
	} else {
		send();                 // beacon 0 doesn't wait
		timer = round;
	}
	
	while(1) {                      // entering permanent state 
		receive();
		if (timer == 0) {       // timeout
			send();         
			timer = round;  
		} else if (src == prev && abs(timer - T) > RESYNCH_THRESH)
			resynch();
	}
}