From 975a673efd4fcabc21becb8f92f434b432f43265 Mon Sep 17 00:00:00 2001 From: taco Date: Fri, 17 Jul 2026 21:15:09 +1000 Subject: [PATCH] add calcMaxPacketMillis --- src/helpers/radiolib/RadioLibWrappers.cpp | 18 ++++++++++++++++++ src/helpers/radiolib/RadioLibWrappers.h | 6 ++++++ 2 files changed, 24 insertions(+) diff --git a/src/helpers/radiolib/RadioLibWrappers.cpp b/src/helpers/radiolib/RadioLibWrappers.cpp index 5e72336c..7146e47b 100644 --- a/src/helpers/radiolib/RadioLibWrappers.cpp +++ b/src/helpers/radiolib/RadioLibWrappers.cpp @@ -228,3 +228,21 @@ float RadioLibWrapper::packetScoreInt(float snr, int sf, int packet_len) { return max(0.0, min(1.0, success_rate_based_on_snr * collision_penalty)); } + +PacketMillis RadioLibWrapper::calcMaxPacketMillis(uint8_t sf, float bw, uint8_t cr, uint8_t preambleSymbols) { + // based on RadioLib's calculateTimeOnAir() + uint32_t tsym_us = ((uint32_t)10000 << sf) / (bw * 10); + uint32_t sfCoeff1_x4 = (sf == 5 || sf == 6) ? 25 : 17; // 6.25 : 4.25, semtech magic numbers to account for sync word + sfd + + // preamble + syncword + sfd + header + uint32_t preamble_us = (((preambleSymbols + 8) * 4 + sfCoeff1_x4) * tsym_us) / 4; + + // airtime for max packet at current radio settings + uint32_t total_us = _radio->getTimeOnAir(MAX_TRANS_UNIT); + // airtime for payload only (no preamble, header or SOF) + uint32_t payload_us = total_us > preamble_us ? total_us - preamble_us : 4000 - preamble_us; // fallback to 4 secs at worst case + // rescale payload_us for max possible CR + if (cr >= 5 && cr < 8) { payload_us = (payload_us * 8) / cr; } + + return PacketMillis {(preamble_us + 999) / 1000, (payload_us + 999) / 1000}; +} \ No newline at end of file diff --git a/src/helpers/radiolib/RadioLibWrappers.h b/src/helpers/radiolib/RadioLibWrappers.h index 3091832f..e7fef910 100644 --- a/src/helpers/radiolib/RadioLibWrappers.h +++ b/src/helpers/radiolib/RadioLibWrappers.h @@ -3,6 +3,11 @@ #include #include +struct PacketMillis { + uint32_t preambleMillis; // preamble-detect -> header-valid deadline + uint32_t payloadMillis; // header-valid -> rx-done deadline +}; + class RadioLibWrapper : public mesh::Radio { protected: PhysicalLayer* _radio; @@ -47,6 +52,7 @@ public: virtual uint8_t getSpreadingFactor() const { return LORA_SF; } static uint16_t preambleLengthForSF(uint8_t sf) { return sf <= 8 ? 32 : 16; } void updatePreamble(uint8_t sf) { _preamble_sf = sf; _radio->setPreambleLength(preambleLengthForSF(sf)); } + PacketMillis calcMaxPacketMillis(uint8_t sf, float bw, uint8_t cr, uint8_t preambleSymbols); virtual int16_t performChannelScan(); int getNoiseFloor() const override { return _noise_floor; }