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Rethinking demodulation code using interrupts

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This commit is contained in:
Rodrigo Alfonso
2025-02-11 04:29:25 -03:00
parent 965e927e3a
commit ad7775740b
3 changed files with 74 additions and 53 deletions
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87
lib/iwram_code/LinkIR.cpp
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@@ -31,65 +31,84 @@ LINK_CODE_IWRAM bool LinkIR::receive(u16 pulses[],
bool hasStarted = false;
bool isMark = false;
u32 pulseIndex = 0;
u32 initialTime = 0;
u32 lastTransitionTime = 0;
firstLightTime = 0;
lastLightTime = 0;
transitionCount = 0;
startCount();
initialTime = getCount();
u32 initialTime = getCount();
linkGPIO.setSIInterrupts(true);
while (true) {
// begin a fixed demodulation window
u32 windowStart = getCount();
u32 transitionsCount = 0;
bool previousRaw = isDetectingLight();
u32 currentLastLightTime = lastLightTime; // (mutated via interrupts)
u32 currentFirstLightTime = firstLightTime; // (mutated via interrupts)
u32 now = getCount();
u32 timeSinceLastLight = now - currentLastLightTime;
// sample for a fixed window duration
while (getCount() - windowStart < DEMODULATION_SAMPLE_WINDOW_CYCLES) {
bool currentRaw = isDetectingLight();
if (currentRaw != previousRaw) {
transitionsCount++;
previousRaw = currentRaw;
}
}
// Transitions
bool isCarrierPresent = transitionsCount >= DEMODULATION_MIN_TRANSITIONS;
u32 transitionTime = getCount();
// new transition?
if (isCarrierPresent != isMark) {
if (!hasStarted && isCarrierPresent) {
// first mark initializes the capture
hasStarted = true;
lastTransitionTime = transitionTime;
} else if (hasStarted) {
// record the pulse duration in microseconds
if (pulseIndex >= maxEntries - 1)
break;
u32 pulseDuration =
(transitionTime - lastTransitionTime) / CYCLES_PER_MICROSECOND;
if (!isMark && transitionCount > DEMODULATION_MARK_MIN_TRANSITIONS) {
// [space ->] mark
if (hasStarted) {
u32 pulseDuration = (currentFirstLightTime - lastTransitionTime) /
CYCLES_PER_MICROSECOND;
pulses[pulseIndex++] = pulseDuration;
lastTransitionTime = transitionTime;
if ((int)pulseIndex >= (int)maxEntries - 2)
break;
}
isMark = isCarrierPresent;
isMark = true;
lastTransitionTime = currentFirstLightTime;
hasStarted = true;
}
if (hasStarted && isMark &&
timeSinceLastLight >=
DEMODULATION_SPACE_THRESHOLD * CYCLES_PER_MICROSECOND) {
// mark -> space
u32 pulseDuration =
(currentLastLightTime - lastTransitionTime) / CYCLES_PER_MICROSECOND;
pulses[pulseIndex++] = pulseDuration;
if ((int)pulseIndex >= (int)maxEntries - 2)
break;
isMark = false;
lastTransitionTime = currentLastLightTime;
transitionCount = 0;
}
// Timeouts
u32 timeSinceLastTransition = now - lastTransitionTime;
u32 timeSinceInitialization = now - initialTime;
// if we've started and we're in a space, check for timeout
if (hasStarted && !isMark &&
((getCount() - lastTransitionTime) / CYCLES_PER_MICROSECOND >=
signalTimeout))
timeSinceLastTransition >= signalTimeout * CYCLES_PER_MICROSECOND)
break;
// if we haven't started and we've waited too long, timeout too
if (!hasStarted &&
((getCount() - initialTime) / CYCLES_PER_MICROSECOND >= startTimeout))
timeSinceInitialization >= startTimeout * CYCLES_PER_MICROSECOND)
break;
}
pulses[pulseIndex] = LINK_IR_SIGNAL_END;
stopCount();
linkGPIO.setSIInterrupts(false);
return pulseIndex > 0;
}
LINK_CODE_IWRAM void LinkIR::_onSerial() {
if (!isEnabled)
return;
detected = true;
lastLightTime = getCount();
if (transitionCount == 0)
firstLightTime = lastLightTime;
transitionCount++;
}
/**
* NOTES:
* To modulate a signal at 38kHz, we need to stay 13.15µs LOW and 13.15µs HIGH.