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Code Issues Releases Activity

Flight/Telemetry Avoid bunching of periodic updates by spreading them.

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git-svn-id: svn://svn.openpilot.org/OpenPilot/trunk@739 ebee16cc-31ac-478f-84a7-5cbb03baadba
This commit is contained in:
vassilis 2010-06-11 02:24:26 +00:00 committed by vassilis
parent 7ec7a5f207
commit b6160c8a9b
1 changed files with 21 additions and 2 deletions
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23
flight/OpenPilot/UAVObjects/eventdispatcher.c
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@ -67,6 +67,7 @@ static int32_t processPeriodicUpdates();
static void eventTask();
static int32_t eventPeriodicCreate(UAVObjEvent* ev, UAVObjEventCallback cb, xQueueHandle queue, int32_t periodMs);
static int32_t eventPeriodicUpdate(UAVObjEvent* ev, UAVObjEventCallback cb, xQueueHandle queue, int32_t periodMs);
static uint32_t randomizePeriod(uint32_t periodMs);
/**
@ -217,7 +218,7 @@ static int32_t eventPeriodicCreate(UAVObjEvent* ev, UAVObjEventCallback cb, xQue
objEntry->evInfo.cb = cb;
objEntry->evInfo.queue = queue;
objEntry->updatePeriodMs = periodMs;
objEntry->timeToNextUpdateMs = 0;
objEntry->timeToNextUpdateMs = randomizePeriod(periodMs); // avoid bunching of updates
// Add to list
LL_APPEND(objList, objEntry);
// Release lock
@ -249,7 +250,7 @@ static int32_t eventPeriodicUpdate(UAVObjEvent* ev, UAVObjEventCallback cb, xQue
{
// Object found, update period
objEntry->updatePeriodMs = periodMs;
objEntry->timeToNextUpdateMs = 0;
objEntry->timeToNextUpdateMs = randomizePeriod(periodMs); // avoid bunching of updates
// Release lock
xSemaphoreGiveRecursive(mutex);
return 0;
@ -354,3 +355,21 @@ static int32_t processPeriodicUpdates()
return timeToNextUpdate;
}
/**
* Return a psedorandom integer from 0 to periodMs
* Based on the Park-Miller-Carta Pseudo-Random Number Generator
* http://www.firstpr.com.au/dsp/rand31/
*/
static uint32_t randomizePeriod(uint32_t periodMs)
{
static uint32_t seed = 1;
uint32_t hi, lo;
lo = 16807 * (seed & 0xFFFF);
hi = 16807 * (seed >> 16);
lo += (hi & 0x7FFF) << 16;
lo += hi >> 15;
if (lo > 0x7FFFFFFF) lo -= 0x7FFFFFFF;
seed = lo;
return (uint32_t)( ((float)periodMs * (float)lo) / (float)0x7FFFFFFF );
}