Recently, my program to read sentences on my GPS card (GPS Ultimate Logging Shield) crashes in the self.readline() routine of the GPS class in the adafruit_gps.py module. Here is the routine to which I added print commands to find the deadlock. The program never returns from the self.readline() routine.
Code: Select all
def _read_sentence(self):
# Parse any NMEA sentence that is available.
# pylint: disable=len-as-condition
# This needs to be refactored when it can be tested.
# Only continue if we have at least 11 bytes in the input buffer
print(f"self.in_waiting {self.in_waiting} bytes")
if self.in_waiting < 11:
return None
print("Read sentence")
sentence = self.readline()
print("Sentence read")
if sentence is None or sentence == b"" or len(sentence) < 1:
return None
try:
sentence = str(sentence, "ascii").strip()
except UnicodeError:
return None
# Look for a checksum and validate it if present.
if len(sentence) > 7 and sentence[-3] == "*":
# Get included checksum, then calculate it and compare.
expected = int(sentence[-2:], 16)
actual = 0
for i in range(1, len(sentence) - 3):
actual ^= ord(sentence[i])
if actual != expected:
return None # Failed to validate checksum.
# copy the raw sentence
self._raw_sentence = sentence
return sentence
# At this point we don't have a valid sentence
return None
To confirm that my program was not in question, I returned to the test program offered on the Adafruit site. I also used my second Metro M4 Airlift Lite microcontroller. But the problem remains. And here I am looking for other possible solutions to my problem.
Copy of the test program. For the needs of my project, note that for the adafruit_gps.py module, I added a 'nmea_sentence_type' property to be able to easily retrieve the type of the sentence being processed without having to put the module in 'debug' mode. This is the reason for the 'dirty' suffix to the module name used in my example.
Code: Select all
# test_serial_connexion_UART.py
# SPDX-FileCopyrightText: 2021 ladyada for Adafruit Industries
# SPDX-License-Identifier: MIT
# Simple GPS module demonstration.
# Will wait for a fix and print a message every second with the current location
# and other details.
import time
import board
import busio
from my_lib import adafruit_gps_dirty as adafruit_gps
# Create a serial connection for the GPS connection using default speed and
# a slightly higher timeout (GPS modules typically update once a second).
# These are the defaults you should use for the GPS FeatherWing.
# For other boards set RX = GPS module TX, and TX = GPS module RX pins.
uart = busio.UART(board.TX, board.RX, baudrate=9600, timeout=10)
# for a computer, use the pyserial library for uart access
# import serial
# uart = serial.Serial("/dev/ttyUSB0", baudrate=9600, timeout=10)
# If using I2C, we'll create an I2C interface to talk to using default pins
# i2c = board.I2C()
# Create a GPS module instance.
gps = adafruit_gps.GPS(uart, debug=False) # Use UART/pyserial
# gps = adafruit_gps.GPS_GtopI2C(i2c, debug=False) # Use I2C interface
# Initialize the GPS module by changing what data it sends and at what rate.
# These are NMEA extensions for PMTK_314_SET_NMEA_OUTPUT and
# PMTK_220_SET_NMEA_UPDATERATE but you can send anything from here to adjust
# the GPS module behavior:
# https://cdn-shop.adafruit.com/datasheets/PMTK_A11.pdf
# Turn on the basic GGA and RMC info (what you typically want)
gps.send_command(b"PMTK314,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0")
# Turn on just minimum info (RMC only, location):
# gps.send_command(b'PMTK314,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0')
# Turn off everything:
# gps.send_command(b'PMTK314,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0')
# Turn on everything (not all of it is parsed!)
# gps.send_command(b'PMTK314,1,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0')
# Set update rate to once a second (1hz) which is what you typically want.
gps.send_command(b"PMTK220,1000")
# Or decrease to once every two seconds by doubling the millisecond value.
# Be sure to also increase your UART timeout above!
# gps.send_command(b'PMTK220,2000')
# You can also speed up the rate, but don't go too fast or else you can lose
# data during parsing. This would be twice a second (2hz, 500ms delay):
# gps.send_command(b'PMTK220,500')
# Main loop runs forever printing the location, etc. every second.
last_print = time.monotonic()
while True:
# Make sure to call gps.update() every loop iteration and at least twice
# as fast as data comes from the GPS unit (usually every second).
# This returns a bool that's true if it parsed new data (you can ignore it
# though if you don't care and instead look at the has_fix property).
gps.update()
# Every second print out current location details if there's a fix.
current = time.monotonic()
if current - last_print >= 1.0:
last_print = current
if not gps.has_fix:
# Try again if we don't have a fix yet.
print("Waiting for fix...")
continue
# We have a fix! (gps.has_fix is true)
# Print out details about the fix like location, date, etc.
print("=" * 40) # Print a separator line.
print(
"Fix timestamp: {}/{}/{} {:02}:{:02}:{:02}".format(
gps.timestamp_utc.tm_mon, # Grab parts of the time from the
gps.timestamp_utc.tm_mday, # struct_time object that holds
gps.timestamp_utc.tm_year, # the fix time. Note you might
gps.timestamp_utc.tm_hour, # not get all data like year, day,
gps.timestamp_utc.tm_min, # month!
gps.timestamp_utc.tm_sec,
)
)
print("Latitude: {0:.6f} degrees".format(gps.latitude))
print("Longitude: {0:.6f} degrees".format(gps.longitude))
print(
"Precise Latitude: {:2.}{:2.4f} degrees".format(
gps.latitude_degrees, gps.latitude_minutes
)
)
print(
"Precise Longitude: {:2.}{:2.4f} degrees".format(
gps.longitude_degrees, gps.longitude_minutes
)
)
print("Fix quality: {}".format(gps.fix_quality))
# Some attributes beyond latitude, longitude and timestamp are optional
# and might not be present. Check if they're None before trying to use!
if gps.satellites is not None:
print("# satellites: {}".format(gps.satellites))
if gps.altitude_m is not None:
print("Altitude: {} meters".format(gps.altitude_m))
if gps.speed_knots is not None:
print("Speed: {} knots".format(gps.speed_knots))
if gps.track_angle_deg is not None:
print("Track angle: {} degrees".format(gps.track_angle_deg))
if gps.horizontal_dilution is not None:
print("Horizontal dilution: {}".format(gps.horizontal_dilution))
if gps.height_geoid is not None:
print("Height geoid: {} meters".format(gps.height_geoid))
Thank you for the help you will give me.
