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Adjust cycle starts when RTIMER_ARCH_SECOND not a power of two.

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This commit is contained in:
David Kopf 2012-01-10 12:48:39 -05:00
parent 58298f59db
commit 24d58edf15
1 changed files with 34 additions and 1 deletions
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35
core/net/mac/contikimac.c
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@ -96,12 +96,24 @@ struct hdr {
};
#endif /* WITH_CONTIKIMAC_HEADER */
/* CYCLE_TIME for channel cca checks, in rtimer ticks. */
#ifdef CONTIKIMAC_CONF_CYCLE_TIME
#define CYCLE_TIME (CONTIKIMAC_CONF_CYCLE_TIME)
#else
#define CYCLE_TIME (RTIMER_ARCH_SECOND / NETSTACK_RDC_CHANNEL_CHECK_RATE)
#endif
/* CHANNEL_CHECK_RATE is enforced to be a power of two.
* If RTIMER_ARCH_SECOND is not also a power of two, there will be an inexact
* number of channel checks per second due to the truncation of CYCLE_TIME.
* This will degrade the effectiveness of phase optimization with neighbors that
* do not have the same truncation error.
* Define SYNC_CYCLE_STARTS to ensure an integral number of checks per second.
*/
#if RTIMER_ARCH_SECOND & (RTIMER_ARCH_SECOND - 1)
#define SYNC_CYCLE_STARTS 1
#endif
/* Are we currently receiving a burst? */
static int we_are_receiving_burst = 0;
/* Has the receiver been awoken by a burst we're sending? */
@ -348,14 +360,35 @@ powercycle(struct rtimer *t, void *ptr)
{
PT_BEGIN(&pt);
#if SYNC_CYCLE_STARTS
static volatile rtimer_clock_t sync_cycle_start;
static volatile uint8_t sync_cycle_phase;
sync_cycle_start = RTIMER_NOW();
#else
cycle_start = RTIMER_NOW();
#endif
while(1) {
static uint8_t packet_seen;
static rtimer_clock_t t0;
static uint8_t count;
#if SYNC_CYCLE_STARTS
/* Compute cycle start when RTIMER_ARCH_SECOND is not a multiple of CHANNEL_CHECK_RATE */
if (sync_cycle_phase++ == NETSTACK_RDC_CHANNEL_CHECK_RATE) {
sync_cycle_phase = 0;
sync_cycle_start += RTIMER_ARCH_SECOND;
cycle_start = sync_cycle_start;
} else {
#if (RTIMER_ARCH_SECOND * NETSTACK_RDC_CHANNEL_CHECK_RATE) > 65535
cycle_start = sync_cycle_start + ((unsigned long)(sync_cycle_phase*RTIMER_ARCH_SECOND))/NETSTACK_RDC_CHANNEL_CHECK_RATE;
#else
cycle_start = sync_cycle_start + (sync_cycle_phase*RTIMER_ARCH_SECOND)/NETSTACK_RDC_CHANNEL_CHECK_RATE;
#endif
}
#else
cycle_start += CYCLE_TIME;
#endif
packet_seen = 0;