[HECnet] Speaking of IDLE

[Paul_Koning at Dell.com]

On Jun 4, 2012, at 6:22 PM, Johnny Billquist wrote:

On 2012-06-04 13:52, Brian Hechinger wrote:
Anyone know how it works? I'd really like to get it working on Solaris.

Simple. For a VAX, simh tries to detect the instruction sequence that the OS do in the idle loop. That's why it depends on which OS you are running on the emulated machine.

For a PDP-11 it is (supposedly) simpler, since hopefully the idle loop of the OS uses the PDP-11 WAIT instruction, but that actually depends on which OS we're talking about. Not sure that RT-11 do, for instance. (I have some vague memory of discussing this with someone a few years ago, and coming to the realization that not all PDP-11 software might be using the WAIT.)

For other hardware and OS combinations, the answers might differ even more.

The doc says that RT and Unix do it differently (no WAIT).   I haven't seen the Unix code but I did see the one for RT (F/B version), and indeed, no WAIT instruction there.   I'm not sure why not.   RT11 S/J seems to just be full of spin loops, no central idle of any kind that I can see.

	paul