[Simh] vax idle for NetBSD

[Paul Koning]

> On Nov 15, 2018, at 10:21 AM, Mark Pizzolato <Mark at infocomm.com> wrote:
> 
> Hi Paul,
> 
> On Thursday, November 15, 2018 at 6:32 AM, Paul Koning wrote:
>> I just installed NetBSD/VAX V8 on SIMH.  The documentation mentions "set
>> cpu idle=netbsd", but it doesn't work -- I'm stuck at 100% CPU.
>> 
>> I'm running it on the microvax3900 simulator, if that makes a difference.  Any
>> ideas?
> 
> I thought this had gotten settled a long time ago.  
> 
> At one point, the BSD code that implemented what the OS does when there is nothing else to do got changed from how things were done in earlier BSD kernels.  The big change seemed to align with when SMP support was added to the kernel to support other (non VAX) architectures.  This restructuring created some platform specific routine which existed to do what was good on that platform while idling.  As it turned out, what was initially implemented in the VAX specific code that did that was operationally indistinguishable from other code running elsewhere in the OS, and given that on those kernel versions idling wasn't possible under simh.  Someone (I don't recall who) had come along and complained about this and after explaining the issue, I suggested that if the VAX specific routine were changed to do something that wasn't done anywhere else in the OS simh idling support could once again work.  When I was poking around, I observed that nothing in any BSD kernel used IPL 1 for anything, so I suggested that the kernel idle routine could set IPL to 1 could be an indicator that simh could detect and properly idle.  The party who had complained passed this suggestion back as a VAX platform specific patch and it ultimately was included in the kernel and it worked for subsequent versions.
> 
> Maybe this change has gotten removed from the VAX specific BSD code in recent versions, or maybe something else is going on with your simh configuration that is interfering with idling.
> 
> I can't find a VAX platform NetBSD 8.0 ISO image, or I'd have checked out what is happening before writing this.  If you can make the disk image and your configuration file available for me.  I'll explore the details and let you know what is happening.

I just followed these instructions: http://www.netbsd.org/ports/vax/emulator-howto.html using the 8.0 image found via the link on that page.

	paul