15 Apr
2015
15 Apr
'15
7:04 a.m.
{Replies to all three recent posts bundled together to reduce list traffic;
hope that's OK...}
From: Glen Slick
> Actually, the PMI signals are all (I'm pretty
sure, but have not
> checked) just like most other QBUS signals - 'broadcast'
> bi-directionally down a transmission line.
when PMI memory boards are installed above and
adjacent to the M8190
CPU the PMI signals are bused through one PMI memory board to the one
above and adjacent to it
At a low level, yes; but I'm trying to understand PMI at a higher level - one
that applies across _all_ backplanes, including the 11/84 backplane, which is
a purer implementation of 'PMI is just another broadcast bus'.
From: Johnny Billquist
> PMI signals are all (I'm pretty sure, but have
not checked) just like
> most other QBUS signals - 'broadcast' bi-directionally down a
> transmission line.
I checked (Micronote #30, 11/84 Tech Manual) and this is basically correct;
all the additional PMI signals are implemented as bi-directional transmission
lines (although some are only used uni-directionally, e.g. PMAPE, PUBSYS,
etc). The UNIBUS adapter does use the BDMG and BIACK lines, which are
uni-directional grant lines, but they are both actually QBUS signals.
But because of the way the CD slots are wired, it
cannot be a general
broadcast thing.
Repeat previous reply to Glen...
> My impression is that the CPU does not get
involved in DMA access to
> PMI memory.
This is one thing I'd like to check though. And I
think this is my
point of worry...
I couldn't find any 11/83 manuals online. There is a User Manual for the
KDJ11-B, and it indicates (Section 1.6.1) that DMA devices can become QBUS
masters and do any normal data transfer over the QBUS, which I take to mean
that the CPU is not involved (other than to do the initial
arbitration). Section 7.3 confirms this.
> I'm pretty sure that whether PMI memory works
as PMI memory or QBUS
> memory depends only on what it hears on the busses, and nothing else.
The memory works as PMI or plan Qbus memory simply
based on where it is
located in relationship to the CPU
Again, that's looking at one special case (the Q/CD backplane); I'd rather
look at PMI in a more general way.
From: Pete Turnbull
QBus non-PMI memory does work (as QBus memory) if
placed before the CPU.
That part I was pretty sure about (given the way the QBUS works). The part I
didn't know was whether an M8190 would work correctly with a mix of PMI and
non-PMI memory.
I wonder what it does - does it start a PMI cycle, and then convert to a QBUS
cycle when the PMI doesn't happen? Or does it somehow scan for both types
during startup, and have some sort of configuration table that it relies on
thereafter? I didn't see anything in either the KDJ11-B or KDJ11-E User
Manual, and there is no KDJ11-x Tech Manual that I could find.
Noel