My favorite hardware bug

Adi Oltean asks: What's your favorite Bug?

My personal favorite was on the ICL PWS-400.  The ICL PWS-400 was a custom hardware design built by ICL. I was on the team of 5 (two from Microsoft, three from ICL) whose job it was to port MS-DOS 4.1 to this new hardware.  The cool thing about the PWS-400 was that it had some custom hardware that allowed real mode applications to access bank switched memory in 4K pages.  This allowed apps to run in the background without impacting running applications.

Since the five of us we were the entire development team, we also did a lot of ad-hoc testing.  One of my personal favorites was running a game that Valorie had brought me from school.  I'm not sure which game it was now, but every time I played it, when it got to a specific spot, the machine would spontaneously reboot.

We put the machine under an ICE (in circuit emulator - a hardware tool that lets you see what's going on inside and outside the CPU) and discovered that the CPU was being externally reset.  That ruled out some wierd software bug.

The hardware guys took the game and the machine and started looking.

After a couple of days, they came back to me and announced they'd found the problem.  It turns out that the trace on the motherboard for the PC speaker was too close to the trace on the motherboard for the CPU reset line.  When you played a specific sound on the PC speaker, EMF emissions from the speaker trace would cause the CPU reset to go high, which caused the CPU to reboot.

 

Gotta love working with hardware :)

Comments

• Anonymous
  August 29, 2005
  The comment has been removed

• Anonymous
  August 29, 2005
  From Larry Osterman’s blog: Adi Oltean asks about favorite hardware bugs.
  I have two that I have...

• Anonymous
  August 29, 2005
  The comment has been removed

• Anonymous
  August 29, 2005
  Matt, that's a brilliant bug.
  
  One that happened to me a long time ago: I had a 386SX16 with 1MB of RAM on the mobo. Added 2MB in SIMMs (remember those?). The system then refused to boot. I took the entire system to the store. They opened it up, reseated the SIMMs and started the computer. It booted up just fine.
  
  I returned home and started the system. Same problem as before. Turns out that the problem was caused by the power supply cables being near the SIMMs and causing interference. At the store, they had taken out the power supply to gain access to the SIMMs, moving the cables out of the way and allowing the system to boot.
  
  Yet another hardware problem that can be solved with duct tape.

• Anonymous
  August 29, 2005
  Surely some (but not all) Intel processor errata are due to the same kind of EMI problems.
  
  At a former employer one of many problems was EMI from a board, an ordinary product purchased in the marketplace, putting noise on an IDE cable. Of course it took quite a while to track down the cause of Windows 2000 hanging. Some kinds of absurd operations seemed to be causing hangs, such as a mouse click on a menu item to refresh a view. It finally turned out that when Windows 2000 detected an error in a signal from a CD-ROM drive, Windows 2000 insisted on writing an event to the log file. If the hard drive was using the same IDE cable then the system never came back. Windows NT4, no problem. Windows 2000 with separate IDE cables, no problem (but there were log entries, which started to give a hint).
  
  By the way what does EMF stand for? I learned EMI as electromagnetic interference, not always caused by static on vinyl records ^^ And then here was Matt Williams blaming the sun, but I thought you guys were only supposed to blame linux, 'cause if you blame sun then who's next, sco? ^^

• Anonymous
  August 29, 2005
  EMF can be several things depending on what you're talking about. Usually it's either ElectroMotive Force (i.e. voltage) or ElectroMagnetic Field. If you're talking about interference, it's probably the latter.

• Anonymous
  August 30, 2005
  Many years ago one of our installations with PDP computers would reboot during the night. After weeks of trying to track down the problem, we discovered that the night operator would pull the PDP away from the wall and then go to sleep behind the computer. In his sleep he would knock the plug out of the wall.
  
  :P

• Anonymous
  August 30, 2005
  I changed the plugs and wires in my '97 Cadillac Deville. After about a week, I noticed that the fan motor was making strange noises, and the noises would change relative to the speed of the engine.
  
  It stumped everyone, until the fan motor burned out and we bought a new one, which came bundled with foil EMI shield. It turns out that when I changed the spark plug wires, I left one of the wires too close to the fan motor. The motor's controller used small voltage variations to change the fan's speed, and pulses from the spark plug wire caused the strange fan noises and burned out the motor!
  
  

• Anonymous
  August 30, 2005
  Back in the dark ages of the 1980's I fancied myself a EE. Once frequencies on the boards started to equal that, of say, WIBA-FM all I seemed able to create was EMI radio stations. I knew at that moment in time that my future lay in software.
  

• Anonymous
  August 30, 2005
  The comment has been removed

• Anonymous
  August 30, 2005
  The comment has been removed

• Anonymous
  August 31, 2005
  The best one I came across was an old VAX which was being used in a steelworks for keeping track of material as it was being transported around the site. Everyday, at just after 5pm, the machine would disappear from the network for 5 minutes, and then reappear having logged a reboot. When someone then was sitting in the room with it, nothing happened so we left it alone again and, sure enough, it rebooted again. Eventually we realised that the cleaner had been going in, unplugging the power from the wall to plug in her vacuum cleaner, and then plugging it back in when she left.

• Anonymous
  August 31, 2005
  The comment has been removed

• Anonymous
  August 31, 2005
  That's funny Wound, the same thing happened to Kimbery Tripp.
  
  http://www.lazycoder.com/weblog/index.php/archives/2005/08/05/beware-urban-legends/
  

• Anonymous
  September 05, 2005
  From Larry Osterman’s blog: Adi Oltean asks about favorite hardware bugs.
  I have two that I have come...

• Anonymous
  September 06, 2005
  Norman D:
  
  "'cause if you blame sun then who's next"
  
  Blame it on the rain. (It keeps falling falling.)
  
  Matt W: If the mouse ball was rolling against the plastic rollers, how did the sun make it get confused?

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