Updated Contiki X-MAC to use hardware acks, which allows for tighter timing and results in a lower duty cycle. Hardware acks also make X-MAC more robust against packet losses, as there is a direct way for the CSMA layer to detect loss of data packets. Before, Contiki X-MAC only detected loss of strobes.
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adamdunkels
parent
d51e99a3dd
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09c223f549
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@ -28,7 +28,7 @@
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*
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* This file is part of the Contiki operating system.
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*
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* $Id: xmac.c,v 1.59 2010/10/03 22:46:53 joxe Exp $
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* $Id: xmac.c,v 1.60 2011/01/25 14:31:09 adamdunkels Exp $
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*/
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/**
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@ -137,7 +137,7 @@ struct xmac_hdr {
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cycle. */
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#define ANNOUNCEMENT_TIME (random_rand() % (ANNOUNCEMENT_PERIOD))
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#define DEFAULT_STROBE_WAIT_TIME (7 * DEFAULT_ON_TIME / 8)
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#define DEFAULT_STROBE_WAIT_TIME (5 * DEFAULT_ON_TIME / 8)
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struct xmac_config xmac_config = {
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DEFAULT_ON_TIME,
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@ -415,6 +415,40 @@ register_encounter(const rimeaddr_t *neighbor, rtimer_clock_t time)
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#endif /* WITH_ENCOUNTER_OPTIMIZATION */
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/*---------------------------------------------------------------------------*/
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static int
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detect_ack(void)
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{
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#define INTER_PACKET_INTERVAL RTIMER_ARCH_SECOND / 5000
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#define ACK_LEN 3
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#define AFTER_ACK_DETECTECT_WAIT_TIME RTIMER_ARCH_SECOND / 1000
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rtimer_clock_t wt;
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uint8_t ack_received = 0;
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wt = RTIMER_NOW();
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leds_on(LEDS_GREEN);
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while(RTIMER_CLOCK_LT(RTIMER_NOW(), wt + INTER_PACKET_INTERVAL)) { }
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leds_off(LEDS_GREEN);
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/* Check for incoming ACK. */
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if((NETSTACK_RADIO.receiving_packet() ||
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NETSTACK_RADIO.pending_packet() ||
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NETSTACK_RADIO.channel_clear() == 0)) {
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int len;
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uint8_t ackbuf[ACK_LEN + 2];
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wt = RTIMER_NOW();
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while(RTIMER_CLOCK_LT(RTIMER_NOW(), wt + AFTER_ACK_DETECTECT_WAIT_TIME)) { }
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len = NETSTACK_RADIO.read(ackbuf, ACK_LEN);
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if(len == ACK_LEN) {
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ack_received = 1;
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}
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}
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if(ack_received) {
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leds_toggle(LEDS_RED);
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}
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return ack_received;
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}
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/*---------------------------------------------------------------------------*/
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static int
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send_packet(void)
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{
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rtimer_clock_t t0;
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@ -422,7 +456,8 @@ send_packet(void)
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rtimer_clock_t encounter_time = 0;
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int strobes;
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struct xmac_hdr *hdr;
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int got_strobe_ack = 0;
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uint8_t got_strobe_ack = 0;
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uint8_t got_ack = 0;
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uint8_t strobe[MAX_STROBE_SIZE];
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int strobe_len, len;
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int is_broadcast = 0;
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@ -456,6 +491,8 @@ send_packet(void)
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}
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is_reliable = packetbuf_attr(PACKETBUF_ATTR_RELIABLE) ||
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packetbuf_attr(PACKETBUF_ATTR_ERELIABLE);
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packetbuf_set_attr(PACKETBUF_ATTR_MAC_ACK, 1);
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len = NETSTACK_FRAMER.create();
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strobe_len = len + sizeof(struct xmac_hdr);
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if(len == 0 || strobe_len > sizeof(strobe)) {
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@ -518,6 +555,9 @@ send_packet(void)
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now = RTIMER_NOW();
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wait = ((rtimer_clock_t)(e->time - now)) % (DEFAULT_PERIOD);
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if(wait < 2 * DEFAULT_ON_TIME) {
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wait = DEFAULT_PERIOD;
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}
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expected = now + wait - 2 * DEFAULT_ON_TIME;
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#if WITH_ACK_OPTIMIZATION
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@ -549,7 +589,7 @@ send_packet(void)
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/* Send a train of strobes until the receiver answers with an ACK. */
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/* Turn on the radio to listen for the strobe ACK. */
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on();
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// on();
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collisions = 0;
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if(!is_already_streaming) {
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watchdog_stop();
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@ -563,6 +603,8 @@ send_packet(void)
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while(got_strobe_ack == 0 &&
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RTIMER_CLOCK_LT(RTIMER_NOW(), t + xmac_config.strobe_wait_time)) {
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rtimer_clock_t now = RTIMER_NOW();
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#if 0
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/* See if we got an ACK */
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packetbuf_clear();
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len = NETSTACK_RADIO.read(packetbuf_dataptr(), PACKETBUF_SIZE);
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@ -588,6 +630,7 @@ send_packet(void)
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PRINTF("xmac: send failed to parse %u\n", len);
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}
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}
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#endif /* 0 */
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}
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t = RTIMER_NOW();
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@ -605,8 +648,9 @@ send_packet(void)
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off();
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} else {
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rtimer_clock_t wt;
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on();
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NETSTACK_RADIO.send(strobe, strobe_len);
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#if 1
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#if 0
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/* Turn off the radio for a while to let the other side
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respond. We don't need to keep our radio on when we know
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that the other side needs some time to produce a reply. */
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@ -614,7 +658,12 @@ send_packet(void)
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wt = RTIMER_NOW();
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while(RTIMER_CLOCK_LT(RTIMER_NOW(), wt + WAIT_TIME_BEFORE_STROBE_ACK));
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#endif /* 0 */
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on();
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if(detect_ack()) {
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got_strobe_ack = 1;
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} else {
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off();
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}
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}
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}
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}
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@ -633,8 +682,6 @@ send_packet(void)
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} else {
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off();
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}
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#else /* WITH_ACK_OPTIMIZATION */
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off();
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#endif /* WITH_ACK_OPTIMIZATION */
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/* restore the packet to send */
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@ -644,7 +691,14 @@ send_packet(void)
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/* Send the data packet. */
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if((is_broadcast || got_strobe_ack || is_streaming) && collisions == 0) {
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NETSTACK_RADIO.send(packetbuf_hdrptr(), packetbuf_totlen());
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if(!is_broadcast) {
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if(detect_ack()) {
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got_ack = 1;
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}
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}
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}
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off();
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#if WITH_ENCOUNTER_OPTIMIZATION
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if(got_strobe_ack && !is_streaming) {
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@ -675,7 +729,7 @@ send_packet(void)
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LEDS_OFF(LEDS_BLUE);
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if(collisions == 0) {
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if(!is_broadcast && !got_strobe_ack) {
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if(is_broadcast == 0 && got_ack == 0) {
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return MAC_TX_NOACK;
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} else {
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return MAC_TX_OK;
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@ -781,6 +835,8 @@ input_packet(void)
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acknowledge the strobe and wait for the packet. By using
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the same address as both sender and receiver, we flag the
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message is a strobe ack. */
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waiting_for_packet = 1;
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#if 0
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hdr->type = TYPE_STROBE_ACK;
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packetbuf_set_addr(PACKETBUF_ADDR_RECEIVER,
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packetbuf_addr(PACKETBUF_ADDR_SENDER));
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@ -797,6 +853,7 @@ input_packet(void)
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} else {
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PRINTF("xmac: failed to send strobe ack\n");
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}
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#endif /* 0 */
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} else if(rimeaddr_cmp(packetbuf_addr(PACKETBUF_ADDR_RECEIVER),
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&rimeaddr_null)) {
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/* If the receiver address is null, the strobe is sent to
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