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Fix https://github.com/adafruit/Adafruit_CircuitPython_GPS/issues/105 #115

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Fix https://github.com/adafruit/Adafruit_CircuitPython_GPS/issues/105 #115

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a70bdbc
Change RMC parsing so that datetime values are available even when
tristan-huber Apr 5, 2025
b02081f
Make same RMC parsing update to the newer RMC_4_1 format
tristan-huber Sep 4, 2025
79c6af3
formatting fix
tristan-huber Sep 4, 2025
2a85a48
another formatting fix
tristan-huber Sep 4, 2025
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6 changes: 4 additions & 2 deletions adafruit_gps.py
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@
https://github.com/adafruit/circuitpython/releases

"""

import time
from micropython import const

Expand Down Expand Up @@ -61,7 +62,7 @@
# 0 - _GLL
"dcdcscC",
# 1 - _RMC
"scdcdcffsDCC",
"scDCDCFFsDCC",
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@dhalbert dhalbert Aug 20, 2025

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One q: what does this change do?

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@tristan-huber tristan-huber Aug 21, 2025

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ya! as I recall this change is to ensure that _RMC sentences with missing location data will still get parsed and returned in case they contain other data, eg: datetime.

This string format is interpreted in _parse_data below and generally capital letters indicate an optional value and lowcase indicate a required value. (rereading the code now, this is clearly the case for c vs C but I'm uncertain if the changes to d and f are strictly necessary).

This string in particular corresponds to the RMC format (ie: table 1-11 in this pdf: https://cdn.sparkfun.com/assets/a/3/2/f/a/NMEA_Reference_Manual-Rev2.1-Dec07.pdf ). The changed characters mark latitude, N/S indicator, longitude, E/W indicator and speed+heading as optional values. These values are all absent if the chip has no GPS fix. But other values (eg: UTC time indicated by the first s) may still be present if the chip has an onboard battery clock. And in such a case a partial sentence can now be returned.

# 2 - _GGA
"sdcdciiffsfsIS",
# 3 - _GSA
Expand All @@ -77,7 +78,7 @@
# 8 - _GSV19
"iiiiiiIiiiIiiiIiiiI",
# 9 - _RMC_4_1
"scdcdcffsDCCC",
"scDCDCFFsDCCC",
# 10 - _VTG
"fcFCfcfcC",
)
Expand Down Expand Up @@ -588,6 +589,7 @@ def _parse_rmc(self, data: List[str]) -> bool:
self.fix_quality = 1
else:
self.fix_quality = 0
return True # break early since no fix means no following values will be populated

# Latitude
self.latitude = _read_degrees(parsed_data, 2, "s")
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25 changes: 25 additions & 0 deletions tests/adafruit_gps_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -162,6 +162,31 @@ def test_GPS_update_timestamp_timestamp_utc_was_not_none_new_date_none():
assert gps.timestamp_utc == exp_struct


def test_GPS_update_time_from_RTC_without_fix():
r = b"$GPRMC,210648.000,V,,,,,0.71,105.86,050425,,,N*4E\r\n"
with mock.patch.object(GPS, "readline", return_value=r):
gps = GPS(uart=UartMock())
assert gps.update() is True
exp_time = time.struct_time((2025, 4, 5, 21, 6, 48, 0, 0, -1))
assert gps.has_fix is False
assert gps.timestamp_utc == exp_time
assert gps.datetime == exp_time
assert gps.nmea_sentence == "$GPRMC,210648.000,V,,,,,0.71,105.86,050425,,,N*4E"


def test_GPS_update_time_from_RTC_without_fix_RMC_4_1():
# RMC_4_1 has an extra "Mode" parameter right before the checksum.
r = b"$GPRMC,210648.000,V,,,,,0.71,105.86,050425,,,A,N*23\r\n"
with mock.patch.object(GPS, "readline", return_value=r):
gps = GPS(uart=UartMock())
assert gps.update() is True
exp_time = time.struct_time((2025, 4, 5, 21, 6, 48, 0, 0, -1))
assert gps.has_fix is False
assert gps.timestamp_utc == exp_time
assert gps.datetime == exp_time
assert gps.nmea_sentence == "$GPRMC,210648.000,V,,,,,0.71,105.86,050425,,,A,N*23"


def test_GPS_update_with_unknown_talker():
r = b"$XYRMC,215032.086,A,1234.5678,N,00123.12345,E,0.45,56.35,021021,,,A*7c\r\n"
with mock.patch.object(GPS, "readline", return_value=r):
Expand Down