Simple GPS for Picaxe

; *******************************
; ***** GPS I2C Slave       *****
; *******************************
;    Filename: GPS_Pixaxe  
;    Date:   04/09/2011 
;    File Version: 1.5 
;    Written by:  Marcwolf 
;    Function:  Decode GPS Signals
;    Last Revision:
;    Target PICAXE: 28X2
; ******************************* 

' This should work on any Picaxe with a scratchpad and variable space
' The scratchpad is split into 2 parts
' 0 to 256 (changable as we only really need 130.. But this is only the 
' start for this project.
' and 256 + for info retrieved from the GPS unit (EM406A but can be any)
' The target conept is to have a Slave I2C PicAxe that will gather 
' GPS, Temp, Voltage etc data and present it in the scratchpad
' ready for the master to collect it.
' There is no special speed constraints on this so no SetFreq is needed

Symbol ptrSer = w26  ' Pointer for incoming serial
Symbol ptrI2C = w27  ' Pointer for outgoing I2C
Symbol SerPoke = 256 ' Start of the Scratchpad area of Serial
Symbol I2CPoke = b49 ' Slave I2C store ptr for Master to grab
Symbol PokePtr = b51 ' Temp area for extraction
Symbol Commas = b50  ' # of comma's to start from
Symbol GPSPort = b.7 ' Where is the GPS
' Starts of routine
GPS:
' Clear scratchpad to spaces ready for data
ptr =0: for b0 = 0 to 150 : ptr = b0 : @ptr = 32 : next
 
ptr=SerPoke ' Set pointer to start of GPS store
' Get the GPS info in. Had issues with HSERIn so now just use the scratchpad
serin GPSPort,T4800,("GPGGA"),@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc
pause 100 ' pause to take processing breath
' Get the information
' Search GPS scratchpad for the number of Comma's
' then put the resulting text into the scratchpad
' starting at potion I2CPoke
Commas = 1: gosub GetString : I2CPoke = 0   : gosub PutString ' Time
Commas = 2: gosub GetString : I2CPoke = 30  : gosub PutString ' Lat
Commas = 3: gosub GetString : I2CPoke = 110 : gosub PutString ' E/W
Commas = 4: gosub GetString : I2CPoke = 45  : gosub PutString ' Long 
Commas = 5: gosub GetString : I2CPoke = 115 : gosub PutString ' N/S
Commas = 9: gosub GetString : I2CPoke = 60  : gosub PutString ' MSL
Commas = 10:gosub GetString : I2CPoke = 120 : gosub PutString ' Meters for MSL

' Same again
ptr=SerPoke
serin GPSPort,T4800,("GPRMC"),@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc,@ptrinc
Pause 100
Commas = 2: gosub GetString : I2CPoke = 125 : gosub PutString ' GPS Fix
Commas = 7: gosub GetString : I2CPoke = 75  : gosub PutString ' speed
Commas = 8: gosub GetString : I2CPoke = 90  : gosub PutString ' Direction
Commas = 9: gosub GetString : I2CPoke = 15   : gosub PutString ' Date
' now read out the scratchpad to simulate a I2C Master Read
ptr =0: for b0 = 0 to 150 : ptr = b0: sertxd(@ptr) : next : sertxd(CR,LF)
' you can add other functions and processes.
GOTO GPS

GetString:
' Clear temp mem - 15 Bytes
for b0 = 80 to 95: poke b0,32: next
' Search along the scratchpad for X number of comma's
ptrSer =  SerPoke
ptr = SerPoke -1
b2 = 0  ' count of comma's
do  ' look until we find the comma we are looking for
  if @ptrinc = "," then ' We found a comma
    inc b2 
    if b2 = Commas then exit ' Are we X Comma's along. If so then exit
  end if
loop
' We are at the X comma, check that there is a next character
if @ptrinc = "," then return : end if ' empty string as in ,,
dec ptr :PokePtr = 80 ' Step back one position and reset the temp memory ptr
' Now get the string to the next comma
do
  b0 = @ptrinc ' Get the valid character
  if b0 = "," then  ' Are we at the next delimiter
    exit ' ok jump out of loop
  else
     poke PokePtr, b0 ' put the actual value into the memory store
     inc  PokePtr ' increment memory store ptr
  end if
loop
' nothing more to do.  GPS extract is in bytes 80 to 95 ready for processing
return  

PutString:
' put the memory store back into the correct position of the  SLAVE I2C store
ptr = I2CPoke  ' set pointer to the I2C slave area
For b0 = 80 to 95 ' loop through memory store
   peek b0,b1 ' get the info
   if b1 = 32 then return: end if ' A space - then we are at the end of the string
   @ptrinc  = b1 ' poke the value into the I2C store
next
return