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Old 01-08-2013, 02:55   #1
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Furuno GP-80 GPS. Warning to Users

Received this at work from Furuno.
Anyone with an older model GP-80 should take note

Good day


We have been informed by Furuno that due to a "Week number roll over" problem a number of FURUNO GPS navigators will fail to work after August 11, 2013




The possible failure may happen for the following serial numbers for GP-80:


FURUNO GP-80 with serial number from S/N 2477-0101 to 2477-8512 shipped before June 2000.


The remaining GP-80 S/N 2477-8513 and after are not related with this problem.






Nature of the positioning error and its cause:
The GPS system is synchronized to a different time scale than Coordinated Universal Time (UTC) and
calculates time by counting the number of weeks up to the 1,023rd week. After week 1,023, the week
number count is reset to zero. This is called "GPS week number roll-over".
This roll-over will occur to GP-80 on August 11, 2013, and the week number is reset to the week 0,
which is December 26, 1993. Subsequently, the erroneous date information on the GPS receiver
clock may result in instability in positioning, causing position errors, including failure of GPS position
acquisition, etc.
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Old 01-08-2013, 05:09   #2
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Re: Furuno GP-80 GPS. Warning to Users

Shipped before June 2000... So they had a pretty good bit of use out of their GPS unit and it's time to update to something a little newer I guess.
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Old 01-08-2013, 09:02   #3
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Re: Furuno GP-80 GPS. Warning to Users

Hey! A Y2K bug!

Computers have a real struggle with dates. The addition of a century identifier is just the visible part of the problem.

How do you figure age? This requires converting a date to a base 10 number to allow arithmetic to do its thing. The way this is done is to pick a date in a previous century and write a program that takes the month, day, year that you give it and calculate the number of days since that arbitrary date from the previous century. After you've done this to two dates, you add or subtract those two numbers and then run it thru another program to convert the results back to months, days, years. Sounds like a programming problem.

I once took care of an accounts receivable hospital system written by IBM in the sixties, that on Sept. 21, 1985 the date routine used the last bit of its allocated space, which was the sign-bit and started returning a negative number. Fortunately we knew it was coming.
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Old 05-08-2013, 15:40   #4
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Re: Furuno GP-80 GPS. Warning to Users

It's not the first time this has happened. If I remember right, the last time was in August 1999. The week count in the GPS system is a 0-1023 (12-bits), so every 1023 weeks the problem reoccurs. Careful programming avoids the issue, so it depends on the GPS programming.
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Old 05-08-2013, 18:19   #5
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Re: Furuno GP-80 GPS. Warning to Users

It's a computer, right? Designed and programmed by humans.

It's not the GPS system. Its the Furuno GP-30 GPS device. Specifically it's the amount of space allocated for the date in that particular model.

BTW I would really take issue with you on the 1023 = 12 bits thing. 4 bits = a byte and a computer moves 2 bytes at a time and while in memory places them on half-word boundaries. They don't move odd numbers of bytes! The number 1023 would take 4 bytes, with the left most bit a sign bit to tell if the number was positive or negative.
BTW-2 a computer can only add.
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Old 08-08-2013, 12:45   #6
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Re: Furuno GP-80 GPS. Warning to Users

Yes, the processing chip is a computer.

It has always been quite common in low-speed data systems to optimize (i.e., minimize) the number of bits used to encode any particular value. I have no idea what the GPS system designers were thinking, but the date value in the GPS data is a 12-bit number counting the number of weeks (0-1023) from (I think) January 1, 1980. I distinctly remember having to get a firmware update from Garmin for my old Garmin 65 when this same problem happened in 1999.

While most computers since the early 1970s have been designed around an 8-bit byte, that wasn't always the case. Early computers often used 6 and 7 bit "bytes" and word lengths up to 64 bits.

Modern computers are "defined" with 8-bit bytes, but internally almost never actually manipulate data 8-bits at a time. Memory and cache widths are often 64, 128 or sometimes more bytes at a time. Internally, I suspect that most modern, high-speed processors work on 64-bits at a time and only use less when they absolutely have to.

The normal way to process a 12-bit value was to load 16-bits, AND-off the 4 bits that you didn't want, and process the remainder as a 16-bit number.

in the case of the GPS week-count, it is specified as an unsigned 12-bit value.

WRT a computer only "adding," the original implementations, because hardware was expensive, was to subtract by a complement followed by an add since both of these operations were required for other things and it was easier to use the two operations in sequence than to build special hardware to subtract.

Rick
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Old 08-08-2013, 14:22   #7
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Re: Furuno GP-80 GPS. Warning to Users

Some manufactures make mistakes!


Mainframe manufacturer, IBM and the like went out of there way to save bits. The first IBM mainframe that I worked on had a total of 8k of memory! That was in 1969, and by 1975 I was working with a mainframe of 256k with an additional 256k add-on. We used the additional memory to allow the use of CRT terminals for commutation with the mainframe. (THEY HAD NO OPERATING SYSTEM OF THEIR OWN).
In October of 2000, when I left Stanford I had been working on a IBM mainframe with an MVS operating system that handled 16 sub operating systems each of which could process 8 different tasks at the same time and the whole thing ran in harmony. We also had an application on PC's that could extract data from disk storage maintained by the mainframe for their own needs..

You're correct that mini-computers and PC's use a octal (base 8) numbering system. IBM and Hitachi of Japan continue to manufacture mainframe computers which use a hexadecimal (base 16) numbering system.

As for "adding" on a computer.

in 1854 George Boolean developed the thought process that became the way that computers "think". Google it.

He also proved, mathematically, that if you add a positive number and a negative number together, the positive number would be reduced by the amount of the negative number. It's done by flipping the bits in the logic system he devised and to this day is called "Boolean Algebra". The program that executes when you give the command 'subtracted by" changes the subtracted by number to a minus number and adds the two together. To multiply, you add a number the amount of times you indicate. Division is just a matter of subtraction
The bit to identify the value of a number is generally the left most bit and when the sum of a calculation uses that bit to store a bit, the value of that number is no longer valid.
I say generally because the Burroughs computer was designed to have the value bit on the right side. The engineers at Control Data designed their computer to have both a plus"0" and a minuses "0". A true sob to program.
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Old 08-08-2013, 15:17   #8
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Re: Furuno GP-80 GPS. Warning to Users

Quote:
Originally Posted by John A View Post
.............. The first IBM mainframe that I worked on had a total of 8k of memory! That was in 1969,.................
Ah, John....that brings back some wonderful memories!

The first mainframe I worked on (an RCA301) had a grand total of 10k memory. Into that small space, you had to load the machine-language program, the print table, the OS and, of course, you had to leave a bit of room for the data :-)

Took up a huge space in the basement of a large government building, together with its six big tape drives, paper-tape readers/punches, IBM card readers, line printers, etc.

No FORTRAN or BASIC or COBOL or any of that sissified stuff. Programming was in machine code (binary on this machine). Whole herd of operators, manufacturer's reps, etc., in three round-the-clock shifts. Communication with the computer was via a binary keyboard which looked and played like a piano.

But, hey, we managed to process a payroll of 80,000 employees and still have time left over for mailing lists and other things.

Those were the (long lost) days of tight, elegant programming....because we had to. Nowadays, graphics and "drop-in" program code and bloatware which can do all sorts of fancy things have pushed their way onto the computer stage, along with their inherent bugs and stability and reliability problems!

Bill
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Old 08-08-2013, 15:55   #9
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Re: Furuno GP-80 GPS. Warning to Users

Those were the days! I once spent a day running 300,000 cards thru a IBM Model 81 card sorter to find all the cards with an "H" in column 18. I found 645 cards. I'll never forget that!
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Old 13-08-2013, 08:55   #10
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Re: Furuno GP-80 GPS. Warning to Users

Dear Nigel,
I'm wondering from where you get this information. We only received last year the FQ8-2011-005 regarding this issue and there were no serial numbers mentioned. On Furuno's Technet I can't trace it neither.
But thanks for sharing anyway!
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