import serial, time
import smbus
import math
import RPi.GPIO as GPIO
import struct
import sys
 
ser = serial.Serial('/dev/ttyAMA0',  9600, timeout = 0)	#Open the serial port at 9600 baud
ser.flush()
 
def readlineCR():
    rv = ""
    while True:
        time.sleep(0.001)	# This is the critical part.  A small pause 
        					# works really well here.
        ch = ser.read()        
        rv += ch
        if ch=='\r' or ch=='':
            return rv
 
class GPS:
	#The GPS module used is a Grove GPS module http://www.seeedstudio.com/depot/Grove-GPS-p-959.html
	inp=[]
	# Refer to SIM28 NMEA spec file http://www.seeedstudio.com/wiki/images/a/a0/SIM28_DATA_File.zip
	GGA=[]
 
	#Read data from the GPS
	def read(self):	
		while True:
			# GPS.inp=ser.readline()
			GPS.inp = readlineCR()
			if GPS.inp[:6] =='$GPGGA': # GGA data , packet 1, has all the data we need
				break
			time.sleep(0.1)
		try:
			ind=GPS.inp.index('$GPGGA',5,len(GPS.inp))	#Sometimes multiple GPS data packets come into the stream. Take the data only after the last '$GPGGA' is seen
			GPS.inp=GPS.inp[ind:]
		except ValueError:
			print ""
		GPS.GGA=GPS.inp.split(",")	#Split the stream into individual parts
		return [GPS.GGA]
 
	#Split the data into individual elements
	def vals(self):
		time=GPS.GGA[1]
		lat=GPS.GGA[2]
		lat_ns=GPS.GGA[3]
		long=GPS.GGA[4]
		long_ew=GPS.GGA[5]
		fix=GPS.GGA[6]
		sats=GPS.GGA[7]
		alt=GPS.GGA[9]
		return [time,fix,sats,alt,lat,lat_ns,long,long_ew]
 
g=GPS()
f=open("gps_data.csv",'w')	#Open file to log the data
f.write("name,latitude,longitude\n")	#Write the header to the top of the file
ind=0
while True:
	try:
		x=g.read()	#Read from GPS
		[t,fix,sats,alt,lat,lat_ns,long,long_ew]=g.vals()	#Get the individial values
		print "Time:",t,"Fix status:",fix,"Sats in view:",sats,"Altitude",alt,"Lat:",lat,lat_ns,"Long:",long,long_ew
		s=str(t)+","+str(float(lat)/100)+","+str(float(long)/100)+"\n"	
		f.write(s)	#Save to file
		time.sleep(2)
	except IndexError:
		print "Unable to read"
	except KeyboardInterrupt:
		f.close()
		print "Exiting"
		sys.exit(0)
	except:
		print "Raw String appears to be empty."

import serial, time
import smbus
import math
import RPi.GPIO as GPIO
import struct
import sys
 
ser = serial.Serial('/dev/ttyAMA0',  9600, timeout = 0)	#Open the serial port at 9600 baud
ser.flush()
 
def readlineCR():
    rv = ""
    while True:
        time.sleep(0.001)	# This is the critical part.  A small pause 
        					# works really well here.
        ch = ser.read()        
        rv += ch
        if ch=='\r' or ch=='':
            return rv
 
class GPS:
	#The GPS module used is a Grove GPS module http://www.seeedstudio.com/depot/Grove-GPS-p-959.html
	inp=[]
	# Refer to SIM28 NMEA spec file http://www.seeedstudio.com/wiki/images/a/a0/SIM28_DATA_File.zip
	GGA=[]
 
	#Read data from the GPS
	def read(self):	
		while True:
			# GPS.inp=ser.readline()
			GPS.inp = readlineCR().strip()
			if GPS.inp[:6] =='$GPGGA': # GGA data , packet 1, has all the data we need
				break
			time.sleep(0.1)
		try:
			ind=GPS.inp.index('$GPGGA',5,len(GPS.inp))	#Sometimes multiple GPS data packets come into the stream. Take the data only after the last '$GPGGA' is seen
			GPS.inp=GPS.inp[ind:]
		except ValueError:
			print ""
		GPS.GGA=GPS.inp.split(",")	#Split the stream into individual parts
		return [GPS.GGA]
 
	#Split the data into individual elements
	def vals(self):
		time=GPS.GGA[1]
		lat=GPS.GGA[2]
		lat_ns=GPS.GGA[3]
		long=GPS.GGA[4]
		long_ew=GPS.GGA[5]
		fix=GPS.GGA[6]
		sats=GPS.GGA[7]
		alt=GPS.GGA[9]
		return [time,fix,sats,alt,lat,lat_ns,long,long_ew]
 
g=GPS()
f=open("gps_data.csv",'w')	#Open file to log the data
f.write("name,latitude,longitude\n")	#Write the header to the top of the file
ind=0
while True:
	try:
		x=g.read()	#Read from GPS
		[t,fix,sats,alt,lat,lat_ns,long,long_ew]=g.vals()	#Get the individial values
		print "Time:",t,"Fix status:",fix,"Sats in view:",sats,"Altitude",alt,"Lat:",lat,lat_ns,"Long:",long,long_ew
		s=str(t)+","+str(float(lat)/100)+","+str(float(long)/100)+"\n"	
		f.write(s)	#Save to file
		time.sleep(2)
	except IndexError:
		print "Unable to read"
	except KeyboardInterrupt:
		f.close()
		print "Exiting"
		sys.exit(0)
	except:
		print "Raw String appears to be empty."

Update GroveGPS.py