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' GPS CLOCK
' WhiteWizzard July 2014
' Based on Geoff Graham's code, March 2014
'
' Demonstration of the MAX7219 SPI driven
' This program will get the time from a U-Blox 7 GPS module, add the timezone
' and daylight saving then display on a 40x8 LED Matrix
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'----------------------MAIN----------------------------



' Configuration constants
TimeZone = 0.0 ' hours from GMT (+ or -)

UseDST = 1 ' set to 1 to enable daylight saving time (DST) adjust, 0 to disable
dms = 3 ' the month that DST starts
dhs = 2 ' the hour that DST starts
dme = 10 ' the month that DST ends
dhe = 2 ' the hour that DST ends

' global arrays
DIM md(12), arg$(20)
DATA 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
FOR i = 1 TO 12: READ md(i): NEXT i

OPEN "COM2:9600" AS #1 ' open the GPS serial interface

' this is the main program loop, it never exits
DO
TIMER=0
SF=0
GetRMC:
arg$(0)="": arg$(2)=""
GetGPSRecord ' get a GPS record
if timer>550 then goto ContMain
if arg$(0)<>"GPRMC" then goto GetRMC:
IF arg$(2) = "A" THEN ' we only want the RMC record. "A" means valid record
'? "Fix"
SF=1
' the GPS has the valid time
' first extract the elements of the date/time from the GPS record
year = VAL(RIGHT$(arg$(9), 2)) ' extract the date
month = VAL(MID$(arg$(9), 3, 2))
day = VAL(LEFT$(arg$(9), 2))
hour = VAL(LEFT$(arg$(1), 2)) ' extract the time
min = VAL(MID$(arg$(1), 3, 2))
sec = VAL(MID$(arg$(1), 5, 2))

' convert the time to minutes since midnight 1st Jan 2014
' then add/subtract the timezone and if required add daylight saving
' this calculation takes just 15mS at 40MHz
mins = GetMins(year, month, day, hour, min)
mins = mins + TimeZone * 60 ' adjust for the timezone
IF UseDST THEN ' if we observe daylight saving
IF mins > GetDST(year, dms, dhs) AND mins < GetDST(year, dme, dhe) THEN
mins = mins + 60 ' adjust for AWST DST
ENDIF
ENDIF

' because we will display the time at the start of the next second
' we have to add 1 second to th e current time
sec = sec '+ 1
IF sec >= 60 THEN sec = 0 : mins = mins + 1
' finally convert the minutes back into the current date/time
Time$ = GetTime$(mins)
'Line2$ = GetDate$(mins)

else
if Timer>200 then
SF=0
goto ContMain
endif
goto GetRMC
ENDIF
ContMain:
LoadTime
DispData

LOOP


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' subroutine to get a GPS record into the array arg$()
SUB GetGPSRecord
arg$(0)="": arg$(2)=""
SF=0
timer=0
do
if INPUT$(1, 1) = "$" then exit do ' wait for the start
if Timer>600 then exit sub
loop

Timer = 0
FOR i = 0 TO 20
arg$(i) = "" ' clear ready for data
DO ' loops until a specific exit
x$ = INPUT$(1, 1) ' get the character
IF x$ = "," THEN EXIT DO ' new data item, new field
IF x$ = "*" THEN EXIT SUB ' end of record, so return with it
IF asc(x$)>31 AND ASC(x$)<127 then arg$(i) = arg$(i) + x$ ' add to the data
if Timer>600 then exit sub
LOOP ' keep going
NEXT i ' increment the field
END SUB


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' calculate the minutes since midnight 1st Jan 2014
FUNCTION GetMins(yr, mth, day, hr, min)
GetMins = (yr - 14) * (365 * 24 * 60) + ((yr - 13) \ 4) * (24 * 60)
GetMins = GetMins + (md(mth) * (24 * 60))
GetMins = GetMins + ((day - 1) * (24 * 60))
GetMins = GetMins + (hr * 60)
GetMins = GetMins + min
IF (yr - 16) MOD 4 = 0 AND mth > 2 THEN GetMins = GetMins + (24 * 60)
END FUNCTION


' convert minutes back into the time (as a string)
FUNCTION GetTime$(minutes)
LOCAL hr, min, am$
am$ = "AM"
hr = (minutes \ 60) MOD 24
IF hr > 12 THEN am$ = "PM" : hr = hr - 12
IF hr = 0 THEN hr = 12
min = minutes MOD 60
GetTime$ = STR$(hr) + ":"
GetTime$ = GetTime$ + RIGHT$("0" + STR$(min), 2) + ":"
GetTime$ = GetTime$ + RIGHT$("0" + STR$(sec), 2) + " " + am$
END FUNCTION


' convert minutes back into the date (as a string)
FUNCTION GetDate$(minutes)
LOCAL yr, mth, day, mths$, days$
mths$ = " JanFebMarAprMayJunJulAugSepOctNovDec"
days$ = "SunMonTueWedThuFriSat"
FOR yr = 14 TO 99
IF minutes < GetMins(yr + 1, 1, 1, 0, 0) THEN EXIT FOR
NEXT yr
FOR mth = 1 TO 12
IF minutes < GetMins(yr, mth, 1, 0, 0) THEN EXIT FOR
NEXT mth
mth = mth - 1
day = ((minutes - GetMins(yr, mth, 1, 0, 0)) \ (24 * 60)) + 1
GetDate$ = MID$(days$, ((((minutes \ (24 * 60)) + 3) MOD 7) * 3) + 1,3)+" "
GetDate$ = GetDate$ + RIGHT$(" " + STR$(day), 2)
GetDate$ = GetDate$ + "-" + MID$(mths$,mth*3,3) + "-" + STR$(yr + 2000)
END FUNCTION


' get the minutes that DST will start or end in a month
' modified for UK DST which starts on the LAST Sunday of the month
FUNCTION GetDST(yr, mth, hr)
LOCAL d, m, n
m = GetMins(yr, mth, 1, hr, 0)
d = ((m \ (24 * 60)) + 3) MOD 7
m = m + (((7 - d) MOD 7) * 24 * 60)
n = GetMins(yr, mth + 1, 1, 0, 0)
do while m + (7 * 24 * 60) < n
m = m + (7 * 24 * 60)
loop
GetDST = m
END FUNCTION

FUNCTION GetTime$(minutes)
LOCAL hr, min, am$
'am$ = "AM"
hr = (minutes \ 60) MOD 24
'IF hr >= 12 THEN am$ = “PM”
'IF hr > 12 THEN hr = hr – 12
IF hr = 0 THEN hr = 12
min = minutes MOD 60
GetTime$ = STR$(hr) + ":"
GetTime$ = GetTime$ + RIGHT$("0" + STR$(min), 2) + ":"
GetTime$ = GetTime$ + RIGHT$("0" + STR$(sec), 2) + " " + am$
END FUNCTION

If UseDST Then ‘if we observe daylight saving
If mins < GetDST(year, dme, dhe) OR mins > GetDST(year, dms, dhs) THEN
mins = mins + 60 ‘adjust for AWST DST
EndIf
EndIf

If mins > GetDST(year, dms, dhs) AND mins < GetDST(year, dme, dhe) THEN

IF secs MOD 20 = 0 THEN
PRINT Line1$ " ", Line2$ " " latitude "" ,(arg$(4))"",longitude "",(arg$(6))""

LOOP

IF sec MOD 20 = 0 THEN
PRINT Line1$ " ", Line2$ " " latitude "" ,(arg$(4))"",longitude "",(arg$(6))""

ENDIF
LOOP