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Fix SX1262 errata 15.4 (IQ polarity) and 15.1 (modulation quality)

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Errata 15.4: SetPacketParams resets register 0x0736 to an incorrect
default for IQ polarity. For standard IQ (no inversion), bit 2 must
be SET after every SetPacketParams call. Without this, LoRa RX
demodulation can fail silently while TX continues to work — the
symptom mimics a hardware failure.

Errata 15.1: Register 0x0889 bit 2 controls modulation quality at
different bandwidths. It must be cleared for 500 kHz BW and set for
all others. The previous implementation was a no-op stub.

Both fixes are from the SX1262 datasheet errata (DS_SX1261-2_V2.1)
and apply to all SX1262-based boards.
This commit is contained in:
GlassOnTin 2026-03-29 17:53:28 +01:00
commit 5d2f0b93e3
1 changed files with 28 additions and 3 deletions
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31
sx126x.cpp
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@ -270,9 +270,24 @@ void sx126x::setPacketParams(long preamble_symbols, uint8_t headermode, uint8_t
buf[4] = crc;
buf[5] = 0x00; // standard IQ setting (no inversion)
buf[6] = 0x00; // unused params
buf[7] = 0x00;
buf[8] = 0x00;
buf[7] = 0x00;
buf[8] = 0x00;
executeOpcode(OP_PACKET_PARAMS_6X, buf, 9);
// SX1262 errata section 15.4: IQ polarity is inverted compared to
// SX1276. The SetPacketParams command resets register 0x0736 to an
// incorrect default. For standard IQ (no inversion), bit 2 must be
// SET after every SetPacketParams call. For inverted IQ, bit 2 must
// be CLEARED. Without this fix, LoRa RX demodulation fails silently
// while TX continues to work.
uint8_t iqreg = readRegister(0x0736);
if (buf[5] == 0x00) {
// Standard IQ: set bit 2
writeRegister(0x0736, iqreg | 0x04);
} else {
// Inverted IQ: clear bit 2
writeRegister(0x0736, iqreg & ~0x04);
}
}
void sx126x::reset(void) {
@ -729,7 +744,17 @@ void sx126x::handleLowDataRate() {
}
// TODO: Check if there's anything the sx1262 can do here
void sx126x::optimizeModemSensitivity(){ }
// SX1262 errata section 15.1: Modulation quality with 500 kHz LoRa BW.
// Register 0x0889 bit 2 must be cleared for 500 kHz, set for all other
// bandwidths. Improves receiver sensitivity at non-500 kHz bandwidths.
void sx126x::optimizeModemSensitivity(){
uint8_t reg = readRegister(0x0889);
if (getSignalBandwidth() == 500E3) {
writeRegister(0x0889, reg & 0xFB); // clear bit 2
} else {
writeRegister(0x0889, reg | 0x04); // set bit 2
}
}
void sx126x::setSignalBandwidth(long sbw) {
if (sbw <= 7.8E3) { _bw = 0x00; }