Jochen wrote:
>         You mean it is possible to speak MSCP on a DSSI bus without
>         an additional protocol layer?
>         Or do you mean that (only?) non-DSSI controllers a la RQDXx and
>         KU]DA50 can speak MSCP without SCA/SCS?

And Roar wrote:
         I have got a very strong feeling I was wrong. (Sorry)

>         But if you have to talk SCA/SCS with the DSSI-devices, that might 
> be a
>         problem, since SCA/SCS is not published, and no implementations are
>         available.

In my experience with the SII chip you set up a buffer in its shared memory 
with the MSCP "packet" layed out, and the node number of where you wanted 
it to go at the front. Then you write the that address into the descriptor 
register and the SII chip picks it up and drops it off at the drive.

In my case I was writing the equivalent of the SCSI INQUIRE command, and 
then a bit later, the SII chip interrupts you to tell you that there is a 
new descriptor in its buffers and if you look at it (which I did from the 
kernel debugger because I had just panic'd on the interrupt :-) you can see 
that the drive has returned to you the information you requested.

Questions that were unanswered in my mind when I put this down about this 
time last year were:
         1) maintaining the physical/virtual mapping between the 128KB buffer
            and main memory.
         2) Hooking the MSCP code that was there so that it could fill in
            the packets.
         3) Writing the bus "enumerator" for config so that I could create
            a device instance for each disk I found (tapes I would ignore 
for now)
         4) Hooking send and receive queues through a top level structure that
            would feed/retrieve them from the SII chip.

So I tried last night to get a 'diff' of my build tree from the cvs tree 
but since its from 1.5.1 pre-release, the number of diffs is _huge_ 
relative to the 1.5.2 tree. I'll put a tarball of my sys tree up later 
today for anyone who might want to look at it. What I've not been able to 
find was my code that set up the INQ command. It shouldn't be too hard to 
recreate however.

--Chuck