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comments on time overflow

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This commit is contained in:
wall_e
2025-11-05 10:13:08 +01:00
parent 617dd3153b
commit 2ccf37ce33
1 changed files with 20 additions and 10 deletions
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30
src/asynStreamGeneratorDriver.cpp
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@@ -350,6 +350,13 @@ asynStatus asynStreamGeneratorDriver::writeInt32(asynUser *pasynUser,
void asynStreamGeneratorDriver::receiveUDP() { void asynStreamGeneratorDriver::receiveUDP() {
// TODO fix time overflows // TODO fix time overflows
// Regarding time overflow.
// * the header time stamp is 3 words, i.e. 48 bits.
// * it has a resolution of 100ns
// * so we can cover a maximum of (2^(3*16) - 1) * 1e-7 = 28147497 seconds
// * or about 325 days
// * so maybe this isn't necessary to solve, as long as we restart the
// electronics at least once a year...
const char *functionName = "receiveUDP"; const char *functionName = "receiveUDP";
asynStatus status = asynSuccess; asynStatus status = asynSuccess;
@@ -482,7 +489,8 @@ void asynStreamGeneratorDriver::processEvents() {
size_t countDiffsPtr = 0; size_t countDiffsPtr = 0;
epicsInt32 *rates = new epicsInt32[this->num_channels]; epicsInt32 *rates = new epicsInt32[this->num_channels];
epicsInt32 *countDiff = new epicsInt32[this->num_channels]; epicsInt32 *countDiff = new epicsInt32[this->num_channels];
epicsInt32 *countDiffs = new epicsInt32[this->num_channels * rateAverageWindow]; epicsInt32 *countDiffs =
new epicsInt32[this->num_channels * rateAverageWindow];
uint64_t *timeSpans = new uint64_t[this->num_channels]; uint64_t *timeSpans = new uint64_t[this->num_channels];
epicsTimeStamp lastRateUpdate = epicsTime::getCurrent(); epicsTimeStamp lastRateUpdate = epicsTime::getCurrent();
@@ -616,25 +624,27 @@ void asynStreamGeneratorDriver::processEvents() {
// Careful changing any of these magic numbers until I clean this up // Careful changing any of these magic numbers until I clean this up
// as you might end up calculating the wrong rate // as you might end up calculating the wrong rate
epicsTimeStamp currentTime = epicsTime::getCurrent(); epicsTimeStamp currentTime = epicsTime::getCurrent();
if (epicsTimeDiffInNS(&currentTime, &lastRateUpdate) > minRateSamplePeriod) { if (epicsTimeDiffInNS(&currentTime, &lastRateUpdate) >
timeSpans[countDiffsPtr] = epicsTimeDiffInNS(&currentTime, &lastRateUpdate); minRateSamplePeriod) {
timeSpans[countDiffsPtr] =
epicsTimeDiffInNS(&currentTime, &lastRateUpdate);
uint64_t totalTime = 0; uint64_t totalTime = 0;
for (size_t i = 0; i <= rateAverageWindow; ++i) { for (size_t i = 0; i <= rateAverageWindow; ++i) {
totalTime += timeSpans[i]; totalTime += timeSpans[i];
} }
lastRateUpdate = currentTime; lastRateUpdate = currentTime;
for (size_t i = 0; i <= this->num_channels; ++i) { for (size_t i = 0; i <= this->num_channels; ++i) {
countDiffs[i * rateAverageWindow + countDiffsPtr] = countDiff[i]; countDiffs[i * rateAverageWindow + countDiffsPtr] =
countDiff[i];
uint64_t cnt = 0; uint64_t cnt = 0;
for (size_t j = 0; j <= rateAverageWindow; ++j) { for (size_t j = 0; j <= rateAverageWindow; ++j) {
cnt += countDiffs[i * rateAverageWindow + j]; cnt += countDiffs[i * rateAverageWindow + j];
} }
rates[i] = rates[i] = cnt / (totalTime * 1e-9);
cnt / (totalTime * 1e-9);
countDiff[i] = 0; countDiff[i] = 0;
} }