[unwind]

The Amiga remains magical to me, having grown up programming it and having had more "aahaa!" moments thanks to it than any other computer in particular.

I still have things like this, floating around in my brain somewhere[]:

  .loop: move.w $dff006,$dff180
         btst.b #6,$bfe001
         bne.s  .loop

It was so awesome, a computer with a great CPU, intriguing and poweful custom hardware for graphics/sound, and still a very decent operating system on top. It had it all. Sniff.

[] Somewhere slightly shady, since I mis-remembered the two first register addresses, and also the sign of the /FE0 bit being read by the third instruction. Still, it's been 14 years since I switched to Linux, so I'm kind of happy.

[rryyan]

What does this code do?

[hackermom]

$dff006 is the vertical raster position register, $dff180 is the background color register, and $bfe001 is one of the registers belonging to one of the two CIAs of the Amiga; the piece of code copies 16 bits of data (on the amiga referred to as a "word") from $dff006 to $dff180, checks if bit 6 in $bfe001 is high - the bit that contains the status of the left mouse button of joy/mouse port #1 - and then branches back to the .loop label if the comparison resulted negatively - that is, if the bit was not high.

In plain-speak, it renders vertical green/blue/cyan gradients in the background until the left mouse button is pressed.

(as a side note, I spent 4-5 years coding on the Amiga in the early 90s.)