[Simh] LAVC

[Timothe Litt]

Not just named buffers.  *Virtual* named buffers; the interface takes
pointers to page tables (or, things that look like page tables in a
couple of cases).  Process, system and global entries.  The only
restriction is that all PTEs must be valid (e.g. buffers are virtually
addressed, but must be resident) And interlocked queues shared with the
host for commands and responses.  That's the full 2-stage interlock of
the VAX queue instructions.

And yes, there are virtual circuits established between hosts and
storage controllers. credit-based flow control.

CIport (host-CI) interfaces are among the most complex; they provide a
mostly hardware-managed network stack.  The HSC does disk level
optimization; responses (and partial buffer transfers) happen in any
order, can be interleaved across the named buffers.  The HSC also has a
command processor, and it's possible to do 3rd party IO, as well as
physical backups.

LAVC replaces the PHY, more or less.  Don't forget TMSCP & DUP.

There *is* microcode in the HSC - the K.xxx cards are 290x based (did
the data moving) & had loadable microcodes.  The J11 firmware (pdp-11
code) handles command decoding, scheduling, error reporting & the CLI. 
But the data transfers are off-loaded to microded engines.   If you want
to run the pdp-11 code, you need to emulate those devices too.

There is exception handling when one cable set breaks (don't remember
exactly the division of responsibility); there are also dual port disks
(across HSCs) for redundancy.

That's just off the top of my head.  It's a non-trivial project.  Er,
P.roject.  That's a very large 'P'.

Could be fun.  But non-trivial.  And there are many layers of research
required to get it right.

On 11-Mar-17 16:53, Paul Koning wrote:
>> On Mar 11, 2017, at 4:42 PM, Johnny Billquist <bqt at softjar.se> wrote:
>>
>> On 2017-03-11 22:33, Tim Stark wrote:
>>> Yeah.
>>>
>>> I believe so.  That is possible to replace CI/DSSI physical layer with UDP over IP multicast to embed SCS/MSCP packets to other hosts and HSCs at once.
>> Of course this is doable. The network part itself is not even hard. The big work is actually implementing the CI controller emulation. Once you have the packet to send out, you just send it.
> It's probably not as easy as you might think.  As I mentioned, the CI protocol (SCA) is an RDMA protocol ("named buffers").  If you want to emulate CI, you'd have to emulate that, because the host code that talks to the CI expects that service, and the real CI interfaces provide it on the I/O card.  You could use the LAVC protocol spec (if there is one available) as inspiration, but it may be that LAVC doesn't provide the same application services as SCA does.
>
> 	paul
>
>
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