Firmware can generate NaN values

[mfine]

NaN values are showing up in libsbp (swift-nav/libsbp#128), in particular on cn0 values in tracking messages.

/cc @mookerji

[mfine]

Sample log lines:

{"timestamp": 1429577577, "data": {"sender": 863, "msg_type": 22, "states": [{"state": 1, "prn": 23, "cn0": 0.9774436354637146}, {"state": 1, "prn": 5, "cn0": 1.1590908765792847}, {"state": 1, "prn": 8, "cn0": 0.9618320465087891}, {"state": 1, "prn": 18, "cn0": 1.0597014427185059}, {"state": 1, "prn": 16, "cn0": 1.0}, {"state": 1, "prn": 19, "cn0": 0.7814569473266602}, {"state": 1, "prn": 29, "cn0": 1.7236841917037964}, {"state": 1, "prn": 6, "cn0": NaN}, {"state": 0, "prn": 0, "cn0": -1.0}, {"state": 0, "prn": 0, "cn0": -1.0}, {"state": 0, "prn": 0, "cn0": -1.0}], "crc": 31229, "length": 66, "preamble": 85, "payload": "ARe/OXo/AQUXXZQ/AQigOnY/ARJMpIc/ARAAAIA/AROQDUg/AR2vodw/AQYAAMB/AAAAAIC/AAAAAIC/AAAAAIC/"}, "delta": 203794}
{"timestamp": 1429577704, "data": {"sender": 863, "msg_type": 22, "states": [{"state": 1, "prn": 22, "cn0": 2.492307662963867}, {"state": 1, "prn": 0, "cn0": 1.207692265510559}, {"state": 1, "prn": 19, "cn0": 1.1629629135131836}, {"state": 1, "prn": 28, "cn0": NaN}, {"state": 1, "prn": 20, "cn0": 0.9850746393203735}, {"state": 0, "prn": 11, "cn0": -1.0}, {"state": 0, "prn": 12, "cn0": -1.0}, {"state": 0, "prn": 31, "cn0": -1.0}, {"state": 0, "prn": 19, "cn0": -1.0}, {"state": 0, "prn": 0, "cn0": -1.0}, {"state": 0, "prn": 0, "cn0": -1.0}], "crc": 2865, "length": 66, "preamble": 85, "payload": "ARb4gR9AAQCplZo/ARP425Q/ARwAAMB/ARTaLXw/AAsAAIC/AAwAAIC/AB8AAIC/ABMAAIC/AAAAAIC/AAAAAIC/"}, "delta": 330988}
{"timestamp": 1429577748, "data": {"sender": 863, "msg_type": 22, "states": [{"state": 1, "prn": 5, "cn0": 1.5333333015441895}, {"state": 0, "prn": 11, "cn0": -1.0}, {"state": 1, "prn": 16, "cn0": 0.9343065619468689}, {"state": 1, "prn": 20, "cn0": 1.293233036994934}, {"state": 1, "prn": 15, "cn0": NaN}, {"state": 0, "prn": 12, "cn0": -1.0}, {"state": 0, "prn": 21, "cn0": -1.0}, {"state": 0, "prn": 24, "cn0": -1.0}, {"state": 0, "prn": 28, "cn0": -1.0}, {"state": 0, "prn": 0, "cn0": -1.0}, {"state": 0, "prn": 0, "cn0": -1.0}], "crc": 33752, "length": 66, "preamble": 85, "payload": "AQVERMQ/AAsAAIC/ARC3Lm8/ARSpiKU/AQ8AAMB/AAwAAIC/ABUAAIC/ABgAAIC/ABwAAIC/AAAAAIC/AAAAAIC/"}, "delta": 375178}
{"timestamp": 1429577778, "data": {"sender": 863, "msg_type": 22, "states": [{"state": 1, "prn": 18, "cn0": 1.174242377281189}, {"state": 1, "prn": 7, "cn0": NaN}, {"state": 0, "prn": 29, "cn0": -1.0}, {"state": 0, "prn": 5, "cn0": -1.0}, {"state": 1, "prn": 4, "cn0": 0.9548872113227844}, {"state": 0, "prn": 14, "cn0": -1.0}, {"state": 0, "prn": 20, "cn0": -1.0}, {"state": 1, "prn": 10, "cn0": 0.939393937587738}, {"state": 0, "prn": 24, "cn0": -1.0}, {"state": 0, "prn": 0, "cn0": -1.0}, {"state": 0, "prn": 7, "cn0": -1.0}], "crc": 65142, "length": 66, "preamble": 85, "payload": "ARKTTZY/AQcAAMB/AB0AAIC/AAUAAIC/AQR9c3Q/AA4AAIC/ABQAAIC/AQoffHA/ABgAAIC/AAAAAIC/AAcAAIC/"}, "delta": 405176}
{"timestamp": 1429577781, "data": {"sender": 863, "msg_type": 22, "states": [{"state": 1, "prn": 18, "cn0": 0.7555555701255798}, {"state": 1, "prn": 7, "cn0": 1.2170542478561401}, {"state": 1, "prn": 21, "cn0": 1.0285714864730835}, {"state": 1, "prn": 0, "cn0": 0.8358209133148193}, {"state": 1, "prn": 16, "cn0": NaN}, {"state": 0, "prn": 14, "cn0": -1.0}, {"state": 0, "prn": 20, "cn0": -1.0}, {"state": 0, "prn": 10, "cn0": -1.0}, {"state": 0, "prn": 24, "cn0": -1.0}, {"state": 0, "prn": 0, "cn0": -1.0}, {"state": 0, "prn": 7, "cn0": -1.0}], "crc": 21374, "length": 66, "preamble": 85, "payload": "ARIXbEE/AQdvyJs/ARU7qIM/AQBc+FU/ARAAAMB/AA4AAIC/ABQAAIC/AAoAAIC/ABgAAIC/AAAAAIC/AAcAAIC/"}, "delta": 408376}
{"timestamp": 1429577945, "data": {"sender": 863, "msg_type": 22, "states": [{"state": 1, "prn": 21, "cn0": 0.935251772403717}, {"state": 1, "prn": 6, "cn0": 0.9130434989929199}, {"state": 1, "prn": 11, "cn0": 0.9855072498321533}, {"state": 1, "prn": 17, "cn0": 0.8196721076965332}, {"state": 1, "prn": 10, "cn0": NaN}, {"state": 0, "prn": 5, "cn0": -1.0}, {"state": 0, "prn": 26, "cn0": -1.0}, {"state": 0, "prn": 9, "cn0": -1.0}, {"state": 0, "prn": 12, "cn0": -1.0}, {"state": 0, "prn": 28, "cn0": -1.0}, {"state": 0, "prn": 7, "cn0": -1.0}], "crc": 28723, "length": 66, "preamble": 85, "payload": "ARWpbG8/AQY4vWk/AQs0Snw/AREI1lE/AQoAAMB/AAUAAIC/ABoAAIC/AAkAAIC/AAwAAIC/ABwAAIC/AAcAAIC/"}, "delta": 572174}

[mfine]

Found some Infinity values in Acquisition:

{"timestamp": 1429658424, "data": {"sender": 1497, "msg_type": 21, "prn": 0, "cf": -8491.69921875, "crc": 11043, "length": 13, "snr": Infinity, "cp": 491.0, "preamble": 85, "payload": "AACAfwCA9UPMrgTGAA=="}, "delta": 21051207}
{"timestamp": 1429656694, "data": {"sender": 863, "msg_type": 21, "prn": 13, "cf": -7742.43212890625, "crc": 42065, "length": 13, "snr": Infinity, "cp": 44.5, "preamble": 85, "payload": "AACAfwAAMkJ18/HFDQ=="}, "delta": 19276843}