[HECnet] Speaking of IDLE

[Johnny Billquist]

On 2012-06-05 02:57, Paul_Koning at Dell.com wrote:

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.

Right. I think my discussion with whomever it was actually centered around RT-11 and Unix. I had to go digging in the Unix code (since I have been playing quite a lot with 2.11BSD), and the information is incorrect on Unix. I searched all the way back to 7th edition (if I remember right), and Unix on the PDP-11 is using WAIT, and always have been. If anyone can find any other pointers to any Unix not using WAIT, I'm always interested in hearing. Since I normally only play with 2.11BSD with all kind of patches, I might definitely have missed something in past history.

But thanks on the confirmation for RT-11. I seemed to remember having checked that one and not found any WAIT, but I was way too unsure to claim anything.

	Johnny

-- 
Johnny Billquist                                   || "I'm on a bus
                                                                  ||   on a psychedelic trip
email: bqt at softjar.se                         ||   Reading murder books
pdp is alive!                                         ||   tryin' to stay hip" - B. Idol