LMIC doesn't handle LoRaWAN MAX_FCNT_GAP

[terrillmoore]

Somewhere early on, but after the LMIC started, the core spec added MAX_FCNT_GAP, a regional/network parameter (default 16384) that specifies how far a message count can be from the previous one and still be accepted.

The LMIC code at

arduino-lmic/src/lmic/lmic.c

Lines 814 to 842 in 4eebb4a

	seqno = LMIC.seqnoDn + (u2_t)(seqno - LMIC.seqnoDn);
	if( !aes_verifyMic(LMIC.nwkKey, LMIC.devaddr, seqno, /*dn*/1, d, pend) ) {
	EV(spe3Cond, ERR, (e_.reason = EV::spe3Cond_t::CORRUPTED_MIC,
	e_.eui1 = MAIN::CDEV->getEui(),
	e_.info1 = Base::lsbf4(&d[pend]),
	e_.info2 = seqno,
	e_.info3 = LMIC.devaddr));
	goto norx;
	}
	if( seqno < LMIC.seqnoDn ) {
	if( (s4_t)seqno > (s4_t)LMIC.seqnoDn ) {
	EV(specCond, INFO, (e_.reason = EV::specCond_t::DNSEQNO_ROLL_OVER,
	e_.eui = MAIN::CDEV->getEui(),
	e_.info = LMIC.seqnoDn,
	e_.info2 = seqno));
	goto norx;
	}
	if( seqno != LMIC.seqnoDn-1 || !LMIC.dnConf || ftype != HDR_FTYPE_DCDN ) {
	EV(specCond, INFO, (e_.reason = EV::specCond_t::DNSEQNO_OBSOLETE,
	e_.eui = MAIN::CDEV->getEui(),
	e_.info = LMIC.seqnoDn,
	e_.info2 = seqno));
	goto norx;
	}
	// Replay of previous sequence number allowed only if
	// previous frame and repeated both requested confirmation
	replayConf = 1;
	}

must be changed to match the spec.

[terrillmoore]

Fixed by #378