[assimpleaspossi]

We had a presentation of our new medical instrument to marketing on Wednesday so there was a big push on Monday to get the display up and running perfectly. There was a dot on the screen. I didn't know why there was a dot but I was under pressure to finish everything else. So I semi-ignored it.

The the Engineering Manager walked by. "There's a dot," he said, "Get rid of it before Wednesday."

With all the other things going right with the project, why this dot--a single pixel--was so important drove us all crazy. I ran through the assembly code that handled all this over and over again and couldn't see anything wrong. Never a reported error by the assembler. Neither could the project manager. Stayed at work all night to wrap it all up and, on Wednesday morning, everything was done and working perfectly just as the Engineering Manager walked into the room at 8am.

"That dot is still there."

Like the author of the article, I questioned whether I should be in this line of work. I continued rewriting, assembling, and testing every variation of the code I could. At 3:00PM on Friday, I found the issue.

MOVE B #0,D0

Do you see it? Imagine this is the 1990s, with a green screen monitor and a PDP-11.

[mandarax8]

No I don't see it. Are moving D0 into B? What's the #0 doing?

[assimpleaspossi]

The problem. It's MOVE.B #0,D0

Do you see it now?

[saagarjha]

I assume that’s where the framebuffer is?

[assimpleaspossi]

Yes. Or at least the data for it.