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The Year 2000 problem and the Amiga
Hai!
v podstate to ignorujte, zkousim jen gateway soft...
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This message is forwarded from Area [AMIGA.42] (Mail:Areas/AMIGA.42/)
Original From: Petr Voralek (2:420/98.0)
Original To : All (2:420/98.0)
Original Subj: The Year 2000 problem and the Amiga
Original Date: 20 Sep 98 06:21:55 Message #:
------------------ Beginning of the forwarded Message ------------------
Hai!
Source: http://www.amiga.com/092098-y2k.html
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*The* *Year* *2000* *problem* *and* *the* *Amiga*
To make a long story short, the Amiga in general does not suffer from
the Year 2000 problem in the context known to the PC world.
However, the Amiga faces three distinct date problems and a single,
specific Year 2000 problem with limited scope which will be described
below.
1. /Scope/ /of/ /this/ /document/
The following text refers to Amiga desktop computers built between 1986
and 1997 and only covers computer hardware configurations designed and
built by Commodore-Amiga, Inc.
This specifically excludes 3rd party hardware extensions, such as the
Microbotics "StarBoard" which among other features offered a battery
backed up clock, but it includes Amiga computers built by Amiga
Technologies GmbH and Amiga, Inc.
2. /How/ /the/ /Amiga/ /handles/ /date/ /and/ /time/
The Amiga operating system has always followed the Unix model in
measuring time as the number of seconds that have elapsed since a fixed
point of time. Under AmigaOS that fixed point of time (also known as
`epoch') is 00:00:00 of January 1, 1978 (Unix uses 00:00:00 GMT, January
1, 1970).
The operating system manages time and date through a central component
known as timer.device. This component reads and stores date and time
information using a data structure known as timeval which, in `C'
language notation, is shown below:
struct timeval
{
ULONG tv_secs;
ULONG tv_micro;
};
In this context an ULONG refers to an unsigned 32 bit quantity.
The tv_secs structure member holds the number of seconds that have
elapsed since the AmigaOS epoch and the tv_micro member denotes the
number of microseconds (the 10-9th part of a second) that have elapsed
since the last second has passed.
Until AmigaOS 2.0 was introduced in 1989/1990 the operating system only
provided the methods for time keeping but did not offer any means to
convert the number of seconds elapsed since the AmigaOS epoch into human
readable format. This work was left to application software developers
who implemented different conversion algorithms with varying success.
2.1 /The/ /AmigaDOS/ /date/ /and/ /time/ /handling/ /is/ /special/
"AmigaDOS" and "AmigaOS" are not two names for the same thing. Exactly the opposite is true: AmigaDOS is (in a nutshell) the name of the
AmigaOS layer which implements filing systems and their actions, the
command line interpreter and which handles loading and relocation of
executable binary files. AmigaDOS is more or less a port of the
Cambridge University TRIPOS 32 bit kernel. It has its own peculiar data
structures, including its own version of the timeval structure described
above. The AmigaDOS flavour is known as DateStamp, as shown below:
struct DateStamp
{
LONG ds_Days;
LONG ds_Minute;
LONG ds_Tick;
};
In this context a LONG refers to a signed 32 bit quantity. The ds_Days member contains the number of days (each day consists of
exactly 24 hours) that have passed since the AmigaOS epoch. The ds_Minute member denotes the number of minutes that have passed since
midnight (00:00:00) of the given day and the ds_Tick member contains the
number of "ticks" that have passed since the last minute. A minute consist of 3,000 "ticks", i.e. there are 50 ticks in a second.
AmigaDOS uses DateStamps to describe file and volume creation dates, and
all shell commands follow the same model, i.e. if the system date is set
through the shell Date command, it will calculate time and date in
DateStamp format.
2.2 /Local/ /time/ /vs/ /GMT/
The Amiga operating system never knew the concept of local and global
time. While the AmigaOS 2.1 update (1992) introduced a locale
preferences editor that allowed for the time zone to be selected, the
operating system itself never put this feature to use or encouraged
application software developers to use it. One might argue that with
this background, the AmigaOS was always tuned to local time.
2.3 /How/ /the/ /Amiga/ /maintains/ /its/ /system/ /time/
The early Amiga computer models did not support a battery backed up real
time clock that would keep on ticking and maintaining local time even
until after the machine was switched off. For example, the first Amiga
computer ever (later christened the Amiga 1000) did not offer a battery
backed up clock. For the Amiga 500 the battery backed up clock was an
extra hardware feature one had to buy separately with a memory expansion.
The Amiga 2000 and (with the exception of the Amiga 600 and Amiga 500+
models) all models to follow did feature a built-in battery backed up
clock.
On machines without battery backed up clocks, the Amiga sets its system
time according to the modification date of the boot volume. In other
words, the point of time the last file was modified or created on a disk
would determine the system time. As this was by no means accurate, the
AmigaOS boot process would suggest and prompt you to adjust the system
date once the system had booted (as pictured below).
[ Obrazek WB 1.1 http://www.amiga.com/startup.gif ]
With machines that featured battery backed up clocks, the system time
was read during the boot process. As of AmigaOS versions 1.2 and 1.3 a
special program, called SetClock, was responsible for reading the current
clock settings and setting the system time accordingly. Starting with
AmigaOS version 2.0 that functionality was integrated into the ROM
operating system, making the SetClock utility at least in part redundant.
If the system starts up without being able to set its system time, it
defaults to 00:00:00 January 1, 1978.
3. /Setting/ /and/ /reading/ /the/ /time/
The Amiga offers both a command line interface and a graphical user
interface. Both went through a number of changes over the years as will
be described below.
3.1 /The/ /command/ /line/ /interface/
There are two shell commands which deal with the system date, these
being SetClock and Date. The Date command is for reading and setting the
current system date whereas the SetClock command deals with the battery
backed up clock, it reads and stores the current system time from/in it.
The Date command is of particular interest due to the human readable date
format it uses by default. Today you might invoke the Date command and
receive the following output:
19-Sep-98
As one can see, the year number is limited to two digits only.
Even if a different locale is used (e.g. french), the year will always be
displayed with its two last decimals only. Luckily, this numbering is
consistent with the following rule:
* If the year number is greater than or equal to 78, the year is 1900
plus the number given (i.e. numbers 78..99 indicate years 1978..1999).
* If the year number is smaller 78, the year is 2000 plus the number
given (i.e. numbers 00..77 indicate years 2000..2077).
To set the system time to any year beyond 1999, you reverse the rule,
i.e. entering date 01-jan-01 will set the time to 1 January, 2001.
All versions of the AmigaDOS Date command (version 1.1 through version
37.1) display and parse the data format in the same fashion. They behave
consistently and predictably throughout all Amiga operating system
revisions.
3.2 /The/ /graphical/ /user/ /interface/
The system time is set through the preferences editor which in AmigaOS
versions 1.0-1.3 used to be a single, monolithic program as pictured
below:
[ Obrazek preferenci http://www.amiga.com/prefs11.gif ]
The controls for setting the system time are located in the top left
corner of the window. They allow the last two digits of the year to be
adjusted; the model follows the AmigaDOS Date command in that a year
number smaller than 78 denotes a year in the range 2000..2077 and all
other settings refer to a year in the range 1978..1999.
With the introduction of AmigaOS 2.0, the time preferences editor was
moved into a single program named Time as pictured below:
[ Obrazek WB 2.0 Time preferenci http://www.amiga.com/prefs20.gif ]
In this editor, the year can be entered as a four digit number. However,
the range is limited to the years 1978..2113.
When the AmigaOS 2.1 update was released, the time preferences editor
was revised, as can be seen below:
[ Obrazek WB 2.1 Time preferenci http://www.amiga.com/prefs21.gif ]
Just like with its predecessor, the year can be entered as a four digit
number. In this case, the range is limited to the years 1991..2099.
4. /The/ /problems/
As far as is known today, the Amiga faces four date problems. Two are design problems caused by numeric overflow, one is caused by
hardware limitations and one is a real bug that will strike in the year
2000.
4.1 /Negative/ /time/
As was outlined above, the Amiga measures time in seconds. As it turns out, the number of seconds to accumulate until 19 January,
2046, 03:14:07 will form the largest value a signed 32 bit integer number
will hold. This is not a problem for the time keeping module
(timer.device), but application software and other operating system
components which treat the number of seconds as a signed quantity will
get into trouble one second later: the number of seconds will rise to
2,147,483,648 which in two's complement format represents the negative
number -2,147,483,648.
AmigaDOS, which always treats time as a signed quantity, will consider
this date to be invalid because it is negative. Worse, the ROM date
conversion routines exhibit a bug which, once the date is later than 19 January, 2046, 03:14:07, causes all subsequent date operations to be
inaccurate. The immediate effect this has is that calculations on dates
can be off by more than two years.
This behaviour is consistent through all AmigaOS versions. A fix is not available yet, but research is in progress to investigate
whether this bug may be fixed by updating several AmigaOS modules
(locale.library, dos.library). After all, this bug is "just" a
side-effect of treating an unsigned quantity as signed.
4.2 /Time/ /rolling/ /over/
An unsigned 32 bit integer can hold a maximum value of 4,294,967,295.
When the Amiga has accumulated that many seconds, it will be 7 February,
2114, 06:28:15. One second later the seconds counter will roll over and
restart at 0. In other words, on 7 February, 2114, 06:28:16 the Amiga
will believe that it is midnight on 1 January, 1978.
No fix for this problem is available yet.
4.3 /The/ /battery/ /backed/ /up/ /clock/ /can/ /count/ /only/ /to/ /99/
Amiga computers that feature a battery backed up real time clock use one
of two different hardware designs: either the Oki MSM6242RS (A500, A2000)
or the Ricoh RP5C01 (A3000, A1200, A4000) chip.
As is common with clock chips of that type, the year counter is
implemented as a two digit BCD number. Once it reaches the year 99, the
counter will roll over and start again with 00.
Starting with Amiga operating system version 2.0, the boot process will
read the battery backed up clock time and set the system time
accordingly. This takes place every time the Amiga is reset. Because the year number covers only two digits, the same algorithm as
used by the AmigaDOS Date command is employed. The consequence this has
is that the Amiga system date set at system startup time will always be
in the range 1978..2077. While the system clock will keep on ticking
beyond 31 December, 2077 a system reset will set the clock back to 1
January, 1978.
No fix for this problem is available yet.
4.4 /SetClock/ /stops/ /working/ /in/ /the/ /year/ /2000/
The SetClock program shipped with the Amiga Workbench disk revisions 1.2
and 1.3 exhibits a bug which causes it to miscalculate the battery backed
up clock time starting with the year 2000. It is accurate only for the
years 1978..1999. Once the year counter rolls over to 00, SetClock will
believe that the year is 1978 until the year 2079 is reached; that's when
it will believe that the year is 1979 -- which is not necessarily an
improvement.
Please note that only the SetClock program found on the AmigaOS 1.2 and
1.3 Workbench disks suffers from this problem. Several versions of this
program were distributed, each between 4,000 and 7,000 bytes in size. To tell whether you have a version that works or not, check the file
size; if it is less than 1,000 bytes in size you will probably have the
properly working version. If it is larger than 4,000 bytes, you probably
have the faulty version.
A fix for this problem is provided in this archive
[ ftp://ftp.amiga.com/pub/SetClock_v34.3.lha ]
Download it and unpack it, then read the enclosed SetClock_ReadMe file.
[ ftp://ftp.amiga.com/pub/SetClock_ReadMe ]
Written by Olaf Barthel * (C) Copyright 1998 Amiga, Inc.
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__/// Petr Voralek <nazir@comp.cz>
\XX/ *Nazir* [Team */AMIGA/*] YASNIMS: 16127560
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