SCSI CAM

[Andrew Valencia <vandys@cisco.com> writes:]
> Your comments concerning CAM are good. If I understand the
> architecture, we would talk CAM down into the 1542x adaptor server, and
> implement SCSI-command-set specific servers to sit on top, talk CAM
> down to a particular adaptor, and provide the appropriate interface
> upwards to the clients (SCSI disk would probably look like a WD server,
> perhaps tape would present a single file instead of a directory).

In general, this is true, although the details about the "SCSI-command-
set servers" are also specified in CAM.

In CAM's world, the disk and tape drivers (servers) are called
peripheral drivers (PDRV's for short). At the top, PDRV's system level
interface similar to that of any other device driver in the operating
system (open/close/read/write/ioctl entry points for *nix, for
example). PDRV's do their job by sending SCSI commands down to the
next CAM layer, called the transport (or XPT) layer. The commands are
contained in a data structure called a CCB (CAM Control Block).

One of the jobs of the XPT layer is to route requests from the PDRV's
above to one of the SCSI Interface Modules (SIM's) below. There may be
more than one SIM per system.

SIM's contain HBA (or dumb SCSI chip, etc.) specific code. The 1542x
adptor server would be a SIM module, for example. There could also be
another (probably much larger) SIM responsible for directly handling an
on board NCR53C9x chip.

In general, I think that the CAM architecture maps fairly well into
what people having been talking about doing for vsta. Comments?

                                                Mike Larson
Received on Sun Sep 12 12:05:55 1993