[HECnet] DECnet Implementation and Productization of RSX-11M, 11S, 11D and IAS (was Re: Anonymous FAL (Tops-20))

[Johnny Billquist]

On 2019-07-15 17:36, John Forecast wrote:
> 
> 
>> On Jul 14, 2019, at 11:55 PM, Thomas DeBellis 
>> <tommytimesharing at gmail.com <mailto:tommytimesharing at gmail.com>> wrote:
>>
>> However, there was a pretty vast commonality in the RSX code base.  
>> Specifically, I was wondering about two things:
> 
> Yes and no. Application level code was usually pretty easy to get 
> running on all flavors of RSX-11. However, the internal architecture was 
> split into 2 classes:
> 
> 1. RSX-11D/IAS - mapped systems only
> 
> Device drivers ran as ’tasks’ (processes) with direct access to I/O 
> devices, system memory allocations and some system routines

Not only that. Device drivers were expected to manipulate event flags of 
other tasks directly, and then inform the OS that a significant even 
happened, which could force rescheduling of tasks. And it seems every 
driver had the code to do this work inline in the driver. So all kind of 
I/O completion becomes sortof messy. I think the driver is still 
expected to switch to kernel mode before doing this work, and also copy 
the IOSB data to the requesting task. Not sure exactly how a think like 
a swapped out process was handled in this case, but maybe the task was 
always locked in memory if I/O was active.

> 2. RSX-11M/11S - any PDP-11 system with sufficient memory + devices
> 
> Device drivers ran as part of the ‘kernel’ serialized by the fork block 
> mechanism

Right. And I/O completion is normally handled by a couple of routines in 
the kernel, so the driver itself can be pretty minimal.

> I guess RSX-11M+ could be consider a separate class adding I/D space, 
> supervisor mode and multi-processor support.

Nah. 11M+ is really very similar to 11M. They pretty much share the same 
codebase, but M+ extends some data structures with a bit more 
information, and also adds a couple of more structures to make the 
system more flexible.
The splitting of I/D space, as well as supervisor mode actually have 
very little impact on the kernel. There is obviously a bit more work at 
a context switch, and there are a couple of details around ASTs, which 
can switch between user and supervisor, but much of the rest don't know 
or care. And drivers can pretty much be moved straight over, although 
you normally would want to modify them to take advantage of some nifty 
additional capabilities provided by M+.

>>  1. What is the latest Phase DECnet that 11M will run?  I guess the
>>     last release was 93?
> Phase IV. The last release I see on bitsavers.org 
> <http://bitsaver.org> was 4.5 in Oct 1989

No. Last/latest release was in 1998/1999 (depends on whether you look at 
11M or 11M+). But it was still all just phase IV.

Latest 11M is V4.8, and latest 11M+ is V4.6.
I think they are even available to trailing-edge...

   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