UNIBUS <-> PCI bridge

[Johnny Billquist]

Roger Ivie <rivie at ridgenet.net> wrote:

> On Mon, 10 Aug 2009, Johnny Billquist wrote:
>> Roger Ivie <rivie at ridgenet.net> wrote:
>> Second, the vector transfer isn't a normal bus transfer in the sense of the 
>> device addressing the CPU and transferring a word.
> 
> Page 2-13 of the UNIBUS spec (1979): "INTR is a bus signal asserted by
> an interrupting device *after it becomes bus master* to inform the
> interrupt fielding processor that an interrupt is to be performed and
> that the interrupt vector is present on the D lines."
> 
> Technically, you don't even have an interrupt until the device hands you
> the vector. Which it does as a bus master.

Ah. Yes, I see now (or remember). INTR is a bus transaction, with the 
interrupt fielding processor as the implicit slave.

>> The CPU cannot be a slave, 
>> unless my memory fails me.
> 
> Page 2-14: "INTR is negated upon receipt of the assertion of SSYN from
> the interrupt fielding processor."

I was just remembering the DATI/DATIP/DATO/DATOB transactions, which 
can't address the CPU.
I didn't remember that the vector transfer had it's own operation on the 
bus.

Nice design really. Yes, once your bus request is granted, you can do 
anything on the bus.

>> It's been way many years since I looked at the unibus map of the VAX UBA, but 
>> I can't for my life imagine that it could be any simpler than the Unibus map 
>> of the PDP-11.
> 
> The PDP-11 can map a UNIBUS page to any *word boundary* in the memory
> space. That means there are adders in there somewhere. The VAX
> scatter/gather map just replaces bits 9 and up with the contents of the
> map entry.

Having an adder, or an or with a mask, isn't much different, or 
conceptually any more complex in my eye.

But maybe that is just me. :-)

	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