To:  CAM Committee Participants
             From:  Dal Allan
          Subject:  Layering and Control Blocks

We covered a lot of territory in our meeting last week, but we ran out of 
time to go back and do a recap of what we had covered in the meeting. 

We drew up the layering at Judy Polonsky's prompting and later on agreed to 
truncate the CCB to reduce the amount of overhead that had to be moved over 
from software. We called that the task of the Transport Module, but did not 
name the corresponding Control Block, so here goes with that filled in. 

 +-----------------------+ 
 | OSD Driver            |    Operating System Dependent Control Block 
 +-----------------------+ 
 | Tranport Module       |    Transport Control Block 
 +-----------------------+ 
 | SCSI Interface Module |    Common Access Method Control Block 
 +-----------------------+ 
 | Protocol Hardware     |    Command Descriptor Block
 +-----------------------+ 

Lance Robinson of Storage Dimensions has argued that we are too close to 
SCSI in the CCB, and require too much of the driver writers who just want to 
ask for Reads and Writes. 

I propose that we include simplified requests into the truncated CCB that we 
agreed belonged in the Transport Module. This would give SCSI-insensitive 
capabilities to ISVs, and the same OSD calls would still be used. 

The Transport Module would have to be capable of generating a SCSI CCB from 
the simpified request. I suspect this will cause heartburn for some members 
but it adds the 3rd level of interface that John Webb of Sytron talked about 
(at the December meeting on what ISVs need). 

Any comments?

Dal