CON

  _clkmode      = xtal1 + pll16x
  _xinfreq      = 5_000_000

'SD Card pins:

  DO_PIN        = 22
  CLK_PIN       = 23
  DI_PIN        = 24
  nCS_PIN       = 25

'Serial I/O pins:

  GPS_IN        = 16
  GPS_OUT       = 17
  PC_IN         = 31
  PC_OUT        = 30

'Write indicator:

  LED_PIN       = 26

'Unit ID:

  UNIT          = "0"

'ASCII constants:

  CR            = 13
  LF            = 10

OBJ

  sio   : "FullDuplexSerial"
  gps   : "FullDuplexSerial"
  sd    : "fsrw"

PUB start | ch, i

  gps.start(GPS_IN, GPS_OUT, 0, 4800)
  sio.start(PC_IN, PC_OUT, 0, 9600)
  sd.mount_explicit(DO_PIN, CLK_PIN, DI_PIN, nCS_PIN)
  filename[7] := UNIT
  dira[26]~~

  waitcnt(cnt + clkfreq)
  gps.str(string("$PSRF100,0,4800,8,1,0*0F", CR, LF))   'Switch to SiRF binary protocol at 4800,8,N,1
   
  'Diable Static Navigation
  
  waitcnt(clkfreq + cnt)
  repeat i from 0 to 9
    gps.tx(DisStatNav[i])
   
  'Switch back To NMEA Protocol Message ID 129, leave only GGA and RMC strings and keep speed at 4800
  
  waitcnt(clkfreq / 2 + cnt)
  repeat i from 0 to 31
    gps.tx(BackToNMEA[i]) 
   
  repeat
    waitstr(string("$GPRMC,"))
    getstr(@time, 10)
    'if (time[5] == "0" or time[5] == "5")
      gps.rx
      if (gps.rx == "A")
        gps.rx
        getstr(@lat, 9)
        waitstr(string("N,"))                           'Change to "S" for southern hemisphere.
        getstr(@lon, 10)
        sio.str(@time)
        outa[26]~~                                      'Turn LED on during write, so it won't be interrupted by flipping off the power.
        sd.popen(@filename, "a")                        'Open the file to append data.
        sd.pwrite(@time, strsize(@time))                'Write the time and position line to the file.
        sd.pclose                                       'Do a close to stat the file.
        outa[26]~                                       'Turn off the LED.
      else
        sio.tx("*")
      
PUB waitstr(strptr) | ptr, match

  ptr := strptr
  repeat while match := byte[ptr++]
    if (gps.rx <> match)
      ptr := strptr

PUB getstr(strptr, len)

  repeat len
    byte[strptr++] := gps.rx

DAT

filename      byte      "gpsdata_.txt"
time          byte      "dddddd.ddd,"
lat           byte      "ddmm.mmmm,"
lon           byte      "dddmm.mmmm",13,0

'SiRF Disable Static Navigation, Message ID 143

DisStatNav    byte      $A0,$A2,$00,$02,$8F,$00,$00,$8F,$B0,$B3

'Switch back To NMEA Protocol Message ID 129 at 4800 bauds, leave on GGA and RMC strings updating oce per second.

BackToNMEA    byte      $A0,$A2,$00,$18,$81,$02,$01,$01,$00,$01
              byte      $00,$01,$00,$01,$01,$01,$00,$01,$00,$01
              byte      $00,$01,$00,$01,$00,$01,$12,$C0,$01,$61
              byte      $B0, $B3