C
C	BBC Microcomputer emulation package
C	BBCMOS_TIME - System time functions
C
C	Copyright Peter Coghlan 1996
C
C	These routines are incredibly convoluted because :
C		- Practically nothing including EDIV can process a quadword
C			into a value larger than a longword.
C		- We want the time to the nearest 10ms -
C			Lib$Cvt_From/To_Interal_Time will not do that but
C			does give one value which is good for up to a year.
C		- We want TIME to reflect the VMS uptime which might be years -
C			Sys$NumTim / Lib$Cvt_VecTim makes that very difficult
C			but they do let us work to the nearest 10ms.
C		- A delta time of zero is not allowed for some reason. We must
C			treat zero as a special case and substitute the
C			smallest delta time (100ns) instead.

C	Osword 1 returns the number of 10ms units since the last system boot,
C		unless the time has been reset using Osword 2.

	Subroutine BBC_Time(A, X, Y)

	Implicit None

	Include '($SyiDef)'
	Include '($LibDtDef)'

	Integer Status, Sys$GetTim, Sys$NumTim, Lib$Cvt_VecTim, Lib$GetSyi
	Integer Lib$Sub_Times, Lib$Cvt_From_Internal_Time, Lib$Emul
	Integer Lib$Add_Times, Lib$Cvt_To_Internal_Time, Lib$Ediv

	Integer A, X, Y, Address, Seconds, Hundredths

C	If Y6502_Read_Memory is declared Integer *4, we get errors assigning
C	values larger than 127 to bytes.

	Integer *1 Y6502_Read_Memory

C	The BbcTime structure is extended to 8 bytes in order to use Lib$Emul.

	Structure /BbcTime/
	  Union
	    Map
	      Integer *4	Long0, Long1
	    End Map
	    Map
	      Integer *1	Byte0, Byte1, Byte2, Byte3, Byte4, %Fill(3)
	    End Map
	  End Union
	End Structure

	Structure /Timbuf/
	  Integer *2	Years, Months, Days, Hours, Minutes, Seconds, Csecs
	End Structure

	Integer *4 Realtime(2), BootTime(2), OffsetTime(2), Uptime(2)
	Integer *4 AdjustedTime(2), TimeA(2), TimeB(2), SmallestDelta(2)

	Record /BbcTime/ BbcTime
	Record /Timbuf/ TimeArray

	Logical Add_Time /.False./

C	Default OffsetTime to a delta time of 0 (or 100ns depending on pov)

	Data OffsetTime /ZFFFFFFFF, ZFFFFFFFF/
	Data SmallestDelta /ZFFFFFFFF, ZFFFFFFFF/

	External Lib$_NegTim

C	First, find the address of the control block

	Address = X + Y * 256

C	Get the system uptime in internal form (Time now minus boottime)

	Status = Sys$GetTim(RealTime)
	If (.Not. Status) Call Lib$Signal(%Val(Status))

	Status = Lib$GetSyi(Syi$_BootTime, BootTime, , , , )
	If (.Not. Status) Call Lib$Signal(%Val(Status))

	Status = Lib$Sub_Times(RealTime, BootTime, UpTime)
	If (.Not. Status) Call Lib$Signal(%Val(Status))

C	Osword 1 - Read system clock

	If (A .Eq. 1) Then

C	  Add or subtract any offset set earlier with Osword 2.

	  If (Add_Time) Then
	    Status = Lib$Add_Times(Uptime, OffsetTime, AdjustedTime)
	  Else
	    Status = Lib$Sub_Times(UpTime, OffsetTime, AdjustedTime)
	  Endif
	  If (.Not. Status) Call Lib$Signal(%Val(Status))

C	  Find out how many seconds in the adjusted time

	  Status = Lib$Cvt_From_Internal_Time(Lib$K_Delta_Seconds,
     +			Seconds, AdjustedTime)
	  If (.Not. Status) Call Lib$Signal(%Val(Status))

C	  Also find out how many hundredths of a second in the adjusted time

	  Status = Sys$NumTim(TimeArray, AdjustedTime)
	  If (.Not. Status) Call Lib$Signal(%Val(Status))

C	  Extend TimeArray.Csecs to a longword

	  Hundredths = TimeArray.Csecs

C	  Add the hundredths to 100 times the seconds to get a BBC style time.
C	  Because a delta time can be up to 10000 days (8.64E10 hundredths of
C	  a second) it might not fit in a signed longword (2.15E9). Therefore,
C	  use Lib$Emul to generate the result.

	  Status = Lib$Emul(Seconds, 100, Hundredths, BbcTime)
	  If (.Not. Status) Call Lib$Signal(%Val(Status))

C	  Finally, we have a 5 byte BBC style time - store it for the caller.

	  Call Y6502_Write_Memory(Address + 4, BbcTime.Byte4)
	  Call Y6502_Write_Memory(Address + 3, BbcTime.Byte3)
	  Call Y6502_Write_Memory(Address + 2, BbcTime.Byte2)
	  Call Y6502_Write_Memory(Address + 1, BbcTime.Byte1)
	  Call Y6502_Write_Memory(Address + 0, BbcTime.Byte0)

C	Osword 2 - Set system clock

	Else If (A .Eq. 2) Then

C	  Initialise the top three bytes of the BbcTime quadword to 0

	  BbcTime.Long1 = 0

C	  Put the time we wish to set the clock to in the rest of BbcTime

	  BbcTime.Byte0 = Y6502_Read_Memory(Address + 0)
	  BbcTime.Byte1 = Y6502_Read_Memory(Address + 1)
	  BbcTime.Byte2 = Y6502_Read_Memory(Address + 2)
	  BbcTime.Byte3 = Y6502_Read_Memory(Address + 3)
	  BbcTime.Byte4 = Y6502_Read_Memory(Address + 4)

C	  Separate it out into seconds and hundredths of a second as there
C	  is no library routine which can handle both and also cope with a
C	  full spec delta time. (We can still have problems - the BbcTime
C	  might be larger than a longword after dividing it by 100 but these
C	  problems are not as important as wierd things happening when you try
C	  to read the time after the system has been up for x days.)

	  Status = Lib$Ediv(100, BbcTime, Seconds, Hundredths) 
	  If (.Not. Status) Call Lib$Signal(%Val(Status))

C	  Genetate an internal time from the seconds and one from the hundredths
C	  Treat zero as a special case each time as it is not allowed!

	  If (Seconds .Ne. 0) Then

	    Status = Lib$Cvt_To_Internal_Time(Lib$K_Delta_Seconds,
     +			Seconds, TimeA)
	    If (.Not. Status) Call Lib$Signal(%Val(Status))

	  Else

	    TimeA(1) = SmallestDelta(1)
	    TimeA(2) = SmallestDelta(2)

	  Endif

	  If (Hundredths .Ne. 0) Then

	    TimeArray.Csecs = Hundredths
	    TimeArray.Seconds = 0
	    TimeArray.Minutes = 0
	    TimeArray.Hours = 0
	    TimeArray.Days = 0
	    TimeArray.Months = 0
	    TimeArray.Years = 0

	    Status = Lib$Cvt_Vectim(TimeArray, TimeB)
	    If (.Not. Status) Call Lib$Signal(%Val(Status))

	  Else

	    TimeB(1) = SmallestDelta(1)
	    TimeB(2) = SmallestDelta(2)

	  Endif

C	  Add the two times together

	  Status = Lib$Add_Times(TimeA, TimeB, AdjustedTime)
	  If (.Not. Status) Call Lib$Signal(%Val(Status))

C	  Subtract from the system uptime to arrive at the offset time.
C	  The offset time is subtracted from the system uptime to give
C	  the value returned to the caller when they read the time with
C	  Osword 1.

	  Status = Lib$Sub_Times(Uptime, AdjustedTime, OffsetTime)

C	  If we got a negative result then time was set to a value greater
C	  than uptime. In this case, find out how much greater and set a
C	  flag to note that the offset should be added to the uptime rather
C	  than subtracted as usual. (Why can't delta times be negative?)

	  If (Status .Eq. %Loc(Lib$_NegTim)) Then
	    Status = Lib$Sub_Times(AdjustedTime, Uptime, OffsetTime)
	    Add_Time = .True.
	  Else
	    Add_Time = .False.
	  Endif

	  If (.Not. Status) Call Lib$Signal(%Val(Status))

	Endif

	Return
	End