Pytrack RMC message

[rolandvs]

I was playing with the Pytrack and needed the date/time from the GPS. The $GNRMC string provides the time, date, speed and direction information along with the coordinates.
So I created a quick hack by adding this to the L76GNSS.py code. I only use date and time.

# date time
	def datetime(self, debug=False):
		thetime, debug_timeout = None, False
		if self.timeout != None:
			self.chrono.start()
		nmea = b''
		while True:
			if self.timeout != None and self.chrono.read() >= self.timeout:
				self.chrono.stop()
				chrono_timeout = self.chrono.read()
				self.chrono.reset()
				self.timeout_status = False
				debug_timeout = True
			if self.timeout_status != True:
				gc.collect()
				break
			nmea += self._read().lstrip(b'\n\n').rstrip(b'\n\n')
			gnrmc_idx = nmea.find(b'GNRMC') # find time data long lat
			if gnrmc_idx >= 0:
				gnrmc = nmea[gnrmc_idx:]
				e_idx = gnrmc.find(b'\r\n')
				if e_idx >= 0:
					try:
						gnrmc = gnrmc[:e_idx].decode('ascii')
						gnrmc_s = gnrmc.split(',')
						thetime = (gnrmc_s[1],gnrmc_s[9]) #return time and date
					except Exception:
						pass
					finally:
						nmea = nmea[(gnrmc_idx + e_idx):]
						gc.collect()
						break
			else:
				gc.collect()
				if len(nmea) > 4096:
					nmea = b''
			time.sleep(0.1)
		self.timeout_status = True
		if debug and debug_timeout:
			print('GPS timed out after %f seconds' % (chrono_timeout))
			return(None)
		else:
			return(thetime)

[livius]

@rolandvs
better is usuing some working code which exist on the web
the best i have found is this:
https://github.com/inmcm/micropyGPS/blob/master/micropyGPS.py

it need some modifications and extend error handling.
Also at the end you need to add GLONASS comands to the list.
Work for me like a charm :)

[rolandvs]

Thanks, I'll give it a try. Looks good!

[ozeta]

@livius hi, cannot code right now but i have some questions: what are glonass sentences?

i see that micropygps uses:
'GPRMC', 'GPGGA', 'GPVTG', 'GPGSA', 'GPGSV', 'GPGLL'

from l76 documentation ( here: http://ecksteinimg.de/Datasheet/QuectelL76-LGNSS.pdf )
gnsll fix uses:
GPGSV, GLGSV, GNGLL, GNGSA
in this list, oly gpgsv is implemented in micropyGPS. I can simply add and implement these other 3?

[livius]

@ozeta
Simply add something like this on the list:

 'GNGLL': gpgll

and other commands. As you can see i attache GNGLL to already supported gpgll emthod

[ozeta]

@livius hi, yesterday i figured it out and did this change on my own.

as for error handling what do you refer to? i didn't have any trouble till today

[livius]

@ozeta
you can get IndexError in various places if message is somehow malformed.

[urblau]

this is my solution.....
works quite well , but somtimes i get an memory error....

from machine import Timer
import time
import gc
import binascii
import machine

class L76GNSS:

GPS_I2CADDR = const(0x10)

def __init__(self, pytrack=None, sda='P22', scl='P21', timeout=None):
    if pytrack is not None:
        self.i2c = pytrack.i2c
    else:
        from machine import I2C
        self.i2c = I2C(0, mode=I2C.MASTER, pins=(sda, scl))

    self.chrono = Timer.Chrono()

    self.timeout = timeout
    self.timeout_status = True

    self.reg = bytearray(1)
    self.i2c.writeto(GPS_I2CADDR, self.reg)

def _read(self):
    self.reg = self.i2c.readfrom(GPS_I2CADDR, 64)
    return self.reg

def _convert_coords(self, gngll_s):
    gc.collect()
    #lat = gngll_s[1]
    lat = gngll_s[3]
    lat_d = (float(lat) // 100) + ((float(lat) % 100) / 60)
    #lon = gngll_s[3]
    lon = gngll_s[5]
    lon_d = (float(lon) // 100) + ((float(lon) % 100) / 60)
    #if gngll_s[2] == 'S':
    if gngll_s[4] == 'S':
        lat_d *= -1
    #if gngll_s[4] == 'W':
    if gngll_s[6] == 'W':
        lon_d *= -1
    #zeit = gngll_s[5]
    zeit = gngll_s[1]
    #print("zeit", zeit)
    geschw = gngll_s[7]
    kurs = gngll_s[8]
    datum = gngll_s[9]
    return(lat_d, lon_d, zeit, datum, geschw, kurs)

def coordinates(self, debug=False):
    lat_d, lon_d, zeit, datum, geschw, kurs, debug_timeout = None, None, None, None, None, None, False
    if self.timeout != None:
        self.chrono.reset()
        self.chrono.start()
    nmea = b''
    while True:
        if self.timeout != None and self.chrono.read() >= self.timeout:
            self.chrono.stop()
            chrono_timeout = self.chrono.read()
            self.chrono.reset()
            self.timeout_status = False
            debug_timeout = True
        if self.timeout_status != True:
            gc.collect()
            break
        gc.collect()#######################################################
        if gc.mem_free() <= 25000:#########################################
            print('##############################################################test1 %f' % (gc.mem_free()))##############################
            machine.reset()################################################

        nmea += self._read().lstrip(b'\n\n').rstrip(b'\n\n')
        #gngll_idx = nmea.find(b'GNGLL')
        #print (nmea)
        gngll_idx = nmea.find(b'GNRMC')
        if gngll_idx >= 0:
            gngll = nmea[gngll_idx:]
            e_idx = gngll.find(b'\r\n')
            if e_idx >= 0:
                try:
                    gngll = gngll[:e_idx].decode('ascii')
                    gngll_s = gngll.split(',')
                    #print("gngll_s", gngll_s)
                    lat_d, lon_d, zeit, datum, geschw, kurs = self._convert_coords(gngll_s)
                except Exception:
                    pass
                finally:
                    nmea = nmea[(gngll_idx + e_idx):]
                    gc.collect()
                    break
        else:
            gc.collect()
            if len(nmea) > 4096:
                nmea = b''
        time.sleep(0.1)
    self.timeout_status = True
    if debug and debug_timeout:
        print('GPS timed out after %f seconds' % (chrono_timeout))
        return(None, None, None, None, None, None)
    else:
        gc.collect()
        return(lat_d, lon_d, zeit, datum, geschw, kurs)

[livius]

@urblau said in Pytrack RMC message:

gc.mem_free() <= 25000

why do you reset device under 25K free mem?
And you should analyze where you consume memory.

My pytrack work many days and collect and then send data to the server.

You must carefully manage strings and make calculations.
e.g. previously i have used some implementation from internet about HMC5883L
but when i saw how it eat memory on every run i go into optimized solution.
maybe this point you to some direction:
https://github.com/pycom/pycom-libraries/pull/8/files

sometimes python syntax is evil in limited memory world..