Bring back Blinkenlights!!!

On 20 Apr 2006 07:33:47 -0700, "ghosdog_688" wrote, in part:

It could be done as part of an *emulator*.

In fact, you could perhaps modify a _virtualization_ package to even run your favorite operating system under an emulated CPU - more slowly, of course - and watch the lights blink.

John Savard

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Its been a long time since blinking lights were of any real use. I don't know about other makers but even the IBM Mainframes of the 1980's did not have "blinken lights". 43xx series had a terminal you could use to display memory etc. 30xx had a 43xx. Even the disk drives had a diagnostic unit that had LCD displays. Some of the older stuff still had lights....

What I did is certainly newer than pre-70's machines, but about

20 years ago, after spending a long time on a crushing project, I decided to build such a gadget. The problem with most of those that I looked at was that you could sort of only see the most significant bit, all the rest were lost in the fuzz.

What I chose to do was take an 8 bit wide slice of the address bus, decode that into 256 leds, let the user position that slice on any nibble boundary, and if it wasn't the most significant eight bits to let the user select the upper bits with toggle switches. Then I added decoding to allow selection of any combination of Read, Write, Input, Output, and I think it was M1 on the 8080, the first byte of an instruction fetch.

With that in a dim room it was possible to actually see the global behavior of programs as they ran. And at the opposite extreme, toggling a few switches would allow zooming in on a particular area. Flip a few switches and I could see the 6 glowing leds that were the first byte of six instructions making up the idle loop while the machine was waiting for input.

I built simpler versions of that for the IBM PC up until the 286 and even early 386.

There was a pretty funny reaction to a call I made to a software vendor, telling the person who answered the phone that I saw their newest version of the software had changed the way they did garbage collection, previously I knew it was doing X but with this version I saw they were now doing Y, and I'd like to make a suggestion about they way they could improve this. There was a long pause, I was asked if I might hold a moment, when someone new picked up the phone he asked me to repeat what I had just said, I did, there was an even longer pause, and finally "How do you know this?" I explained and we became great friends, I still use their stuff and do beta test for them.

But after the 386 PC's stopped presenting all the memory addresses to the ISA bus and the method wouldn't work in that form any more.

I purchased a motherboard with the extra 487 socket which gave access to all the memory cycles, at least those not caught by the internal cache, but never completed that prototype.

I believe it is possible to build similar hardware today. I briefly thought about that as a product but never carried through. The best hardware solution that I've thought of is to create a "dummy SIMM" that captures address cycles and transforms this down into a slow stream of bits to drive the bank of leds. Additional hardware can produce an audio stream, varying pitch, tempo and volume so you could hear the behavior if you wanted to.

The "case mod" people today might be willing to pay the price to have such a toy. But a decade ago it didn't look like "the Egghead Software Christmas impulse buyer" would pay what these would cost to sell in small volumes.

Now, "of any real use", I don't go there, not anymore. But if someone really wants to pursue this, I can tell you all the thought and work I put into this. Maybe you could send me one when you get it working, I'd be curious to watch a modern OS run under this, and I've got a big box of leds in the back room I might give you. (I've thought about it and I don't think software is the answer)

Congratulations! Sounds like a good idea.

A variation that is perfectly suited to 8 bit micros with a 16 bit address bus is this: feed the high and low byte of the address bus to two D/A converters, use the analog outputs to drive the X/Y inputs of an oscilloscope. It is amazing how much information you can collect about what your code is doing by just looking at the resulting display. For example, an unlit spot in an area you know belongs to your data ram is data that is not being accessed, the relative intensity of the traces tells you where you are spending most of the time, etc.

Nah, that is too fancy. Just put a small AM radio next to your gear. Again, amazingly useful. (Not always, I concede.). After finding the right spot on the dial we may learn that "chirp" means a particular ISR is being called, that "buzz" comes form that function and so on.

I would be interested. I would like to build (just for fun) an FPGA base computer. Every time I sit to make a few sketches the architecture changes, but the toggle switches and blinkenlights are always there.

Roberto Waltman

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*snip*

Shouldnt be hard at all, many people are doing this now. Get a 150$ development board, grab a few opencores and have a ball.

Later you can drop the cores, and make your own..