A wild bug: 1970s Intel 8271 disc chip ate my data
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A wild bug: 1970s Intel 8271 disc chip ate my data
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Re: A wild bug: 1970s Intel 8271 disc chip ate my data
#2So that's how those Mission Impossible messages to James Bond would self destruct!
Re: A wild bug: 1970s Intel 8271 disc chip ate my data
#3Good reason to get a Gotek floppy emulator and work with copies instead. With the open source FlashFloppy software, they work great, and are pretty cheap.
Re: A wild bug: 1970s Intel 8271 disc chip ate my data
#4Fascinating read, although I take issue with its title that implies that it's a bug in the chip. Maybe a bug in the author's code (when he wrote wrong values to the register), definitely not a bug in the chip but a feature. If you write undocumented values into a register, undocumented stuff happens. A lot of ICs have undocumented test modes that are used by the manufacturer.
Re: A wild bug: 1970s Intel 8271 disc chip ate my data
#5So that's how those Mission Impossible messages to James Bond would self destruct!
Forgive me for being pedantic. The agent's name in Mission Impossibles is Ethan Hunt.
Re: A wild bug: 1970s Intel 8271 disc chip ate my data
#6Pretty interesting behaviour, but I don't think you can claim this is a fault in the controller. The contract was being invalidated when he wrote invalid data to a register. After that, anything may happen.
Today, most hardware has some protection against abuse, but in the days of the BBC micro it was common for hardware and os to completely trust the software. There were plenty of storys of damaged monitors because of invalid timing parameters.
One of my own storys, and I'm a bit hazy so some details are probably wrong: We found an old computer in a university dumpster some night, and decided to mess with the floppy drive. More beer than common sense around. There was some way to tell the hardware which track to read/write, with sane values from 0 to 79. But it was a byte , we could go to 255, so we decided to go up up up!
Well, the drive did exactly as commanded. 80 - 85 worked quite well, except the floppy wasn't guaranteed to be magnetically coated. But once we pushed it too far, the read head went literally over the edge: It jumped off the axle, dropped on the spinning disk below, got a serious yank, and the tiny wires got snapped off.
All of this with a single x86 out instruction, I think in dos 3.x debug. The OS was not stopping you if you did something stupid, there was no hardware protection or anything.
Re: A wild bug: 1970s Intel 8271 disc chip ate my data
#7Pretty interesting behaviour, but I don't think you can claim this is a fault in the controller. The contract was being invalidated when he wrote invalid data to a register. After that, anything may happen. Today, most hardware has some protection against abuse, but in the days of the BBC micro it was common for hardware and os to completely trust the software. There were plenty of storys of damaged monitors because…
At least the drive I accidentally tried the same had a mechanical stop. Although banging the head against it 170 times or so wasn't exactly beneficial for its alignment.
Even today, one is better off not to write undocumented values to registers. True story: I had to investigate a SW bug report concerning a modern, fairly popular microcontroller. (I won't name which.) Sometimes data in RAM changed without our code writing to it. Turns out that our startup code accidentally wrote to a 'reserved' bit in a register, activating some kind of internal RAM test mode. This was confirmed by the µC's manufacturer.
Re: A wild bug: 1970s Intel 8271 disc chip ate my data
#8Pretty interesting behaviour, but I don't think you can claim this is a fault in the controller. The contract was being invalidated when he wrote invalid data to a register. After that, anything may happen. Today, most hardware has some protection against abuse, but in the days of the BBC micro it was common for hardware and os to completely trust the software. There were plenty of storys of damaged monitors because…
Before analog monitors got a builtin delay for changing the video mode, you could intentionally wreck the device by writing a few lines of code in QBasic, and by the time someone had already power cycled the poor machine while troubleshooting, the evidence was long gone.
Re: A wild bug: 1970s Intel 8271 disc chip ate my data
#9Pretty interesting behaviour, but I don't think you can claim this is a fault in the controller. The contract was being invalidated when he wrote invalid data to a register. After that, anything may happen. Today, most hardware has some protection against abuse, but in the days of the BBC micro it was common for hardware and os to completely trust the software. There were plenty of storys of damaged monitors because…
Before analog monitors got a builtin delay for changing the video mode, you could intentionally wreck the device by writing a few lines of code in QBasic, and by the time someone had already power cycled the poor machine while troubleshooting, the evidence was long gone.
I'm not sure if its a good idea, but I'm going to link another of my old timer stories here:
Re: A wild bug: 1970s Intel 8271 disc chip ate my data
#10Pretty interesting behaviour, but I don't think you can claim this is a fault in the controller. The contract was being invalidated when he wrote invalid data to a register. After that, anything may happen. Today, most hardware has some protection against abuse, but in the days of the BBC micro it was common for hardware and os to completely trust the software. There were plenty of storys of damaged monitors because…
At least the drive I accidentally tried the same had a mechanical stop. Although banging the head against it 170 times or so wasn't exactly beneficial for its alignment. Even today, one is better off not to write undocumented values to registers. True story: I had to investigate a SW bug report concerning a modern, fairly popular microcontroller. (I won't name which.) Sometimes data in RAM changed without our code wr…
> Although banging the head against it
This was how an Apple II made sure you were in track zero - by banging the head against the stop. This is why it makes that typical noise when booting up.