Re:Microcode: the place where hardware and software meet
by cynwoody on Sunday March 10, 2013 @04:19PM
(#5353289)
> You can change the operation of instructions after the hardware is made, make custom sequences of instructions, or even fix microcode bugs (while uncommon, there have been cases in the past).
I am reminded of the famous Intel Pentium FDIV bug (1994). Seems they had implemented a new and improved floating point division algorithm. It needed only half the cycles of the previous algorithm.
The new algorithm used a 1066-cell lookup table to find partial quotients used in the calculation. Unfortunately, due to a screwup, five of the cells were left blank when the ROM was loaded. This led to obscure errors in the results, which went unnoticed until many thousands of chips were in customers' hands. At that point, Intel had a massively embarrassing recall on their hands.
I am reminded of the famous Intel Pentium FDIV bug (1994). Seems they had implemented a new and improved floating point division algorithm. It needed only half the cycles of the previous algorithm.
The new algorithm used a 1066-cell lookup table to find partial quotients used in the calculation. Unfortunately, due to a screwup, five of the cells were left blank when the ROM was loaded. This led to obscure errors in the results, which went unnoticed until many thousands of chips were in customers' hands. At that point, Intel had a massively embarrassing recall on their hands.
http://engineeringfailures.org/?p=466
http://www.trnicely.net/pentbug/pentbug.html