Re: Address of second TMSCP controller

[Johnny Billquist <bqt%update.uu.se@localhost>]

On 2021-01-28 23:11, Mark Pizzolato - Info Comm wrote:
> On Thursday, January 28, 2021 at 12:27 PM, Johnny Billquist wrote:
> > RSX basically do explicit address assignment, and only use autoconfiguration
> > in one explicit place in the SYSGEN process, to find out what hardware is
> > installed on your system, to provide some default answers for the SYSGEN
> > process itself. It's not used at any other time.
> >
> > I think RSTS/E made more use of the probing at runtime. Not sure about RT-
> > 11.
> >
> > And how you probe the I/O space is almost as the description above, but not
> > quite. But if someone wants to, we could go over how it is done.
>
> VMS essentially requires that this algorithm is used to assign device addresses.

Definitely not. It is convenient to use that algorithm, but if/when you 
attach devices in SYSGEN in VMS, you can explicitly give the CSR as 
well. Not hard at all.

> The complete details of this process are implemented in the simh VAX and PDP11
> Simulators in the routine auto_config in module PDP11/pdp11_io_lib.c.
> A distinctly lesser cut at this is implemented in the simtools repository config11/config11.c
> module.

Which can be useful, but which have also confused people.

> Given the decades of legacy behavior where device addresses are explicitly declared
> in BSD configurations, it would seem quite late in the day to think about changing
> how things have always worked for BSD.

Yeah. I do not expect that this will change in any BSD. And there is 
certainly also an argument to be made against this scheme.

It's a misery if you ever want to add some hardware, since you have to 
potentially change the settings on a bunch of boards you have in the 
machine. Not something that is ever fun.
Admittedly, that is much less a problem in a simulated environment.

  Johnny

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