String Parsing/Converting

g3cwi · 2012-03-04 00:31

Dear all

I am using the GPS_IO_MINI to extract data from the NMEA information from my GPS. I need to use the velocity and GPS fix quality as numbers. A first attempt failed after which it occured to me that they were probably extracted as strings. First question - is that right?

If they are strings, I need to convert them into decimals. One is an integer (quality), the other is not (velocity). In practice I only need the integer part of the velocity though. Looking around I have found lots of objects that can turn strings into decimals but (newbie alert) they all "return a pointer" and I don't know how to use them. So the second question is where can I find a gentle walkthrough description of using methods that "return a pointer"? If you assume that I have no more programming knowledge than the average Cocker Spaniel you will have the level just right!

Oh and I also need some advice on just getting the integer part of the velocity out of the string!

Time for breakfast.

Regards from rainy England

Richard

kuroneko · 2012-03-04 01:48

Maybe this gets you started http://forums.parallax.com/showthread.php?138045-A-Simple-GPS-Problem. As for returning a pointer, that would be the wrong kind of method/object as you want a number from a string.

g3cwi · 2012-03-04 02:45

Thanks. I have included the Numbers object and have tried:

value := numbers.FromStr(gps.speed, numbers#DEC)

This returns nothing at all so I am still puzzled.

Regards

Richard

kuroneko · 2012-03-04 03:01

What about a minimal test case (or we're here all day/night)?

g3cwi · 2012-03-04 03:06

I rather thought that was the minimal test case! I am happily using the NMEA string for other things but now I need to do some calculations using the data.

As I mentioned, I'm new to this...

Regards

Richard

kuroneko · 2012-03-04 03:16

OK, so what do you get for serial.str(gps.time) (serial being your PC debug connection)?

Next would be to check serial.hex(gps.speed, 8), if that value is NULL then it's not available, otherwise (not equal NULL) what does serial.str(gps.speed) report?

repeat
    waitcnt(clkfreq + cnt)
    if temp := gps.speed
      serial.str(temp)
    else
      serial.str(string("not available", 13))

g3cwi · 2012-03-04 03:28

gps.speed returns "0.00" and gps.valid returns "A".

!5315.80N/00208.80W-0.00 Knots A

I used the numbers object and then added 120 to the "speed" and "333" to the valid, this gave:

<0x06>5<0xfa><0x80>F Knots 0N/

where <0x06>5<0xfa><0x80>F is the speed and;

0N/ is the valid.

I am debugging over an APRS network and clearly it can't interpret these values as decimal numbers so something's wrong!

Regards

Richard

kuroneko · 2012-03-04 03:50

Quick and dirty. Not seeing your code makes it a bit tricky to spot what could be wrong.

CON
  _clkmode = XTAL1|PLL16X
  _xinfreq = 5_000_000
          
OBJ
 fds[2] : "FullDuplexSerial"
 GPS    : "GPS_IO_mini"
 n      : "Numbers"

VAR
  long  stack[32]
  
Pub GPS_Time | value, valid, s_addr

  cognew(helper, @stack{0})                             ' fake GPS emitter
  
  GPS.start(1, 9600)
  fds{0}.start(31, 30, %0000, 115200)

  repeat
    if valid := GPS.valid                               ' get valid state
      fds{0}.str(valid)                                 ' valid
      fds{0}.tx(32)
    else
      fds{0}.str(string("- "))                          ' not valid
    if s_addr := GPS.speed
      fds{0}.str(s_addr)                                ' print as string
      fds{0}.tx(32)
      value := n.FromStr(s_addr, n#DEC)                 ' convert to decimal
      fds{0}.dec(value)                                 ' print as decimal
      fds{0}.tx(13)
    else
      fds{0}.str(string("not available", 13))
    waitcnt(clkfreq + cnt)

PRI helper

  fds[1].start(2, 1, %0000, 9600)
  repeat
    waitcnt(clkfreq*3 + cnt)
    fds[1].str(string("$GPRMC,081836,A,3751.6565,S,14507.3654,E,[COLOR="red"]010.0[/COLOR],360.0,130998,011.3,E*62", 13))
    
DAT

With the code above I send a fake GPS string every 3 seconds and get this output:

- not available
- not available
- not available
A 010.0 10
A 010.0 10
A 010.0 10
...

Note that GPS.speed returns an address to a string. This string must not be manipulated in any way. After convertion you'll get a single long value which is all yours.

g3cwi · 2012-03-04 03:59

Brilliant - and much appreciated. I will experiment!

Regards

Richard

g3cwi · 2012-03-04 06:39

Hair tearing out time. Taking the advice above and using a similar format for the code, I have modified my code to use what I had hoped would be decimal values for gps.valid and gps.speed.

CON

  _clkmode      = xtal1 + pll16x
  _xinfreq      = 5_000_000

  out   =       1  'useful definitions
  in    =       0
  on    =       1
  off   =       0

  'AX25 Modem Definitions
  XMTPIN = 27
  PTTPIN = 25
  TX_LVL = 10

  'LED PORT
  LED = 22

  'GPS Config
  GPS_RX   = 23    'NMEA data sent to this port from GPS
  GPS_Baud = 9_600 'Default for most GPS modules

  
OBJ

  mdm   :  "ax25"        'generates AX25 packet

  gps   :  "GPS_IO_mini" 'Extracts data from GPS NMEA string

  Num   :  "Numbers"     'Used to convert strings into decimals

  Debug :  "Debug_LCD"


VAR

  byte packet[255]
  byte packetcount
  LONG TX_DELAY 'used for timing
  Long valid_dec, speed_dec, speed_addr, valid_addr 'used in string to dec routine

PUB main

    Debug.init(0, 9_600, 4) 'Pin 0, 9_600 baud, 4 lines
    Debug.backlight (true)
    Debug.
    dira~~   'sets all pins to outputs - this help avoid problems with RF
    dira[GPS_RX] := in   'GPS Port set to input
    
 
    mdm.start_simple(mdm#NONE, XMTPIN, PTTPIN, TX_LVL) 'Start AX25
    gps.start(GPS_Rx, GPS_Baud) 'Start GPS

    
    Repeat 5 'Boot indicator
    
      led_(on) 
      waitcnt((clkfreq/10)+cnt) 
      led_(off)
      waitcnt((clkfreq/10)+cnt) 

    repeat 'this is the main loop
    
      valid_addr := gps.valid 'get address of gps.valid
      valid_dec  := num.FromStr(valid_addr, num#DEC) 'convert to decimal
    
        if valid_dec > 0  'Don't send invalid packets
         
          led_(off) 
      
          clearPacket

          fillGPSPacket

          mdm.createPacket(@packet, 1)  '1 means no path included , 0 means full path
     
          mdm.sendPacket

          led_(on) 'Packet dispatched
          
          waitcnt((clkfreq/3)+cnt)
      
          led_(off)

          TX_DELAY := 120 'initialise TX hold off (seconds)

          Repeat until TX_DELAY < 1 'simple adaptive delay
          
            'Conversion from string to decimal
            speed_addr := gps.speed  'get address of gps.speed
            speed_dec  := Num.FromStr(speed_addr, Num#DEC) 'turn string into decimal
            speed_dec  := speed_dec * 100 'multiply by 100 to make integer
          
            IF speed_dec > 2500 'in Knots = 29MPH
            
             TX_DELAY := TX_DELAY - 5 'keep reducing the delay if travelling fast

            waitcnt( clkfreq + cnt ) 'Wait 1 second
            
            TX_DELAY := TX_DELAY - 1 'Decrement delay




PRI fillTestPacket

      addToPacket(string("!5315.60N/00207.70W-"), 20)
      addToPacket(string("***TEST***"), 10)
      'This allow remote debugging via APRS!
      addToPacket(gps.latitude, 7)
      addToPacket(gps.N_S, 1) 
      addToPacket(string("/"), 1)

      addToPacket(gps.longitude, 8)
      addToPacket(gps.E_W, 1) 
      addToPacket(string("-"), 1)
      
      addToPacket(string("Propellor Test 12345"), 20)
     
      addToPacket(0,1)          'end of packet

PRI fillGPSPacket

      addToPacket(string("!"), 1)
      addToPacket(gps.latitude, 7)
      addToPacket(gps.N_S, 1) 
      addToPacket(string("/"), 1)

      addToPacket(gps.longitude, 8)
      addToPacket(gps.E_W, 1) 
      addToPacket(string("-"), 1)
      
      valid_addr := gps.valid
      valid_dec  := num.FromStr(valid_addr, num#DEC)
      valid_dec  := valid_dec + 333
      
      speed_addr := gps.speed
      speed_dec  := num.FromStr(speed_addr, num#DEC)
      speed_dec  := speed_dec * 100
      speed_dec  := speed_dec + 120
            
      'Your data payload goes here
      addToPacket(string("APRS implemented by G3CWI. "), 27)
      addToPacket(string(" Test data follows: "), 20)
      if speed_dec > 119
        addToPacket(string("Speed was 120"),13)
        
      addToPacket(string(" Knots "), 7)
      if valid_dec > 332
        addToPacket(string("Valid was 333+"),14)
       
      addToPacket(0,1)          'end of packet

PUB led_(onoff)

      outa[led] := onoff

PUB addToPacket(straddr, length) | pointer        'no zeros may be added, except at the end!

    pointer := straddr

    repeat length
       if (packetcount<256)
         packet[packetcount++] := byte[pointer++]
        

PUB clearPacket | i

    repeat 255
        packet[i] := 0
        i++
        packetcount := 0

This fails to work as hoped. I am really finding this whole address and content thing most confusing.

Any ideas?

Regards

Richard

g3cwi · 2012-03-04 12:44

Still stuck. Spent all afternoon experimenting and getting nowhere.

I want to change a floating point number into a string.

FloatString has the perfect subroutine:

FloatToFormat(single, width, dp) : stringptr

However, I have been unable to figure out how to use it - the problem being that I don't understand
a) how to get back the string pointer and then
b) how to use it to get the string back.

Assuming my number is stored so that:

test := 123.456

I then tried combinations of:

test := fs.Floattoformat (test, 6, 2)
Debug.str (test)

I tried sprinkling @ signs around but still no joy. I am clearly mis-understanding the whole "address", Pointer, string thing.

Help appreciated.

Regards

Richard

Mike G · 2012-03-04 13:40

I'm not sure what is tripping you up. If it's going from a string to numbers or numbers to strings.

Strings are encoded (we're dealing with ASCII encoding) byte arrays where each byte represents a character. Strings end with a zero. Called zero or null terminated.

This is incorrect syntax

test := 123.456

This is correct syntax

bytemove(@buff, string("123.456"), strsize(string("123.456")))

Hopefully this example helps a bit. This is the first time I used Float32. Someone will correct me if I did not use the object correctly.

CON
    _clkmode = xtal1 + pll16x
    _xinfreq = 5_000_000

DAT
  buff  byte $0[10]
    
OBJ
  pst    : "Parallax Serial Terminal"
  f32    : "Float32"

  
PUB Main | integer, mantissa, ans
  pst.Start(115_200)
  f32.Start
  waitcnt((clkfreq / 1_000 * 1_000) + cnt)

  ' 2 * 3.1416 = 6.2832
  integer := 3 * 2
  mantissa := f32.FFloat(1416)
  mantissa := f32.FMul(mantissa, 2)

  'Write 6.2832
  pst.dec(integer)
  pst.char($2E) ' .
  pst.dec(mantissa)
  pst.char($0D) ' CR
  
  'Write a string
  bytemove(@buff, string("123.456"), strsize(string("123.456")))
  pst.str(@buff)
  pst.char($0D)  ' CR

g3cwi · 2012-03-04 13:48

Hi Mike

Thanks for your interest. The number I have is of the form 123.456 and is a floating point decimal. Basically I need to round it to 0 decimal places (i.e. 123) and then use it as a string. That was the reason for looking at theFloattoFormat method from the FloatString Object. However as I don't really understand the terminology I don't know how to recover the pointer and how to use it to recover the string itself.

Regards

Richard

SteveWoodrough · 2012-03-04 15:16

Richard,
I'm not much further along the trail than you are but I think I just walked your path last week. I've attached my sloppy code that is a work in progress. If I understand your issue correctly, essentially what you need to do is apply the Numbers object. I give an example in the code below. If I'm not mistaken, if you bring in a decimal number into the Prop, say 123.45, you will by default get 123 . I hope I'm not being captain obvious and this helps you out.

Point of order to the experts out there: I noticed that the object GPS_IO_mini does NOT have a STOP method. Should it by convention have a Stop method and that Stop method be part of the Start method?
Regards,
Steve Woodrough

{**************************************************
*      GETTING GPS DATA 4 MARCH 2012              *
*                                                 *
***************************************************
THIS PROGRAM DEMONSTRATES GETTING GPS DATA, PARSING AND CONVERTING STRINGS TO NUMBERS AS WELL
AS SENDING THE DATA TO EITHER THE PST OR LCD.
   
}
CON
 _clkmode        = xtal1 + pll16x
 _xinfreq        = 5_000_000

 RxPin = 1
   CR = 13                                               ' ASCII <CR>
   LF = 10                                               ' ASCII <LF>

{  LCD ASCII Commands
8 Cursor left
9 Cursor right
10 Cursor down (bottom line will wrap to top line)
12 Clears the display
13 goes to next line
21 Turns display off
22 Turns Display ON
128 - 143 along line 0
148 -163 along line 1
}


          
OBJ
 ss     : "Simple_Serial"
 fds    : "FullDuplexSerial"
 GPS    : "GPS_IO_mini"
 n      : "Numbers"
VAR
long Time, ShortTime
  
Pub Main

    GPS_LCD                     'This sould display the GPS data to the LCD.  


Pub GPS_LCD
GPS.start(15,9600)               'Starts the GPS data parser to Rx data at 9600

fds.start(-1,4,1,19_200)   ' Data to LCD via FDS (No Rx Pin, Tx on Pin 4, Mode 0 or 1, 19_200 Baud)     
 FDS.tx(22)                  'Turn LCD ON   
 waitcnt(clkfreq/20+cnt)
 FDS.tx(12)                  'Clears screen  
 
'fds.start(31,30,0,57600)        'Sending data to PST via FDS   

repeat
   fds.tx(12)                  'Clears screen
   fds.tx(128)                 'move cursor
   Display_Longitude 
   fds.tx(140)                 'move cursor
   Display_Speed
   
   fds.tx(148)                 'move cursor
   Display_Latitude
   fds.tx(160)
   Display_Heading
   
   waitcnt(clkfreq/2+cnt)
   
Pub Display_Longitude

   fds.str(GPS.longitude)            'Transmits string pointer
    
Pub Display_Latitude

    fds.str(GPS.latitude)            'Transmits string pointer
    
Pub Display_Heading

    fds.str(GPS.Heading)            'Transmits string pointer

Pub Display_Speed

    fds.str(GPS.Speed)            'Transmits string pointer    
   
Pub Display_Time
    
    fds.str(String("GPS String = "))
    fds.str(GPS.time)            'Transmits string pointer to PST displaying the current time                    
    fds.tx(CR)
    fds.tx(LF)

    
    fds.str(String("GPS Time as Variable 'TIME' = ")) 'Converts the string value of time to a 10 digit decimal 
    Time := n.FromStr(GPS.time,10)                     'Using BASE 10 format
    fds.dec(Time)

    
    ShortTime:=Time-5                  'Just playing around and proving to myself that I actually have a real number
    fds.str(String(" ShortTime = "))   'Of course when "Time" ends with 00 the value of ShortTime ends in 95 but that
    fds.dec(ShortTime)                 'was not the point of the exercise

                    
    fds.tx(CR)
    fds.tx(LF)
     
    waitcnt(clkfreq+cnt)        'wait a second just to keep too much data from going to the PST

Pub GPS_String_to_PST|x                'This routine works just fine and sends the NMEA strings to the PST
 ss.init(15,-1,9600)             'Message in on pin 15, no TX (-1) and 9600 baud 
  
 fds.start(31,30,0,57600)       'Sending data to PST must be turned off to use VP terminal 
  
 repeat
   
   x:=ss.rx                     'Receive a byte on pin 3 from the GPS

  fds.tx(x)                    'Transmits data to PST works great w/o VP active

kuroneko · 2012-03-04 15:29

g3cwi wrote: »

Hair tearing out time. Taking the advice above and using a similar format for the code, I have modified my code to use what I had hoped would be decimal values for gps.valid and gps.speed.
...
This fails to work as hoped.

What did you expect to happen and what does happen? Note that the valid indicator (valid_addr) can be NULL so converting this will give you unexpected results. Furthermore, the returned string is "A" which can't be converted to decimal. So AFAIAC looking at NULL/not NULL should be enough for a valid indication. The speed retrieval looks OK apart from a NULL check (not sure if that field is mandatory).

g3cwi · 2012-03-05 12:47

Thanks all for your patience. I am now up and running. Part of the problem was my ineffective debug facilities. I now have a serial 4 x 20 LCD so I can actually see what is happening.

'Till the next problem

regards

Richard

String Parsing/Converting

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