Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!rpi!uupsi!grebyn!ckp From: ckp@grebyn.com (Checkpoint Technologies) Newsgroups: comp.arch Subject: Re: Info. on DEC's Mass Storage Protocol Message-ID: <20009@grebyn.com> Date: 5 May 90 03:19:23 GMT References: <34955@shemp.CS.UCLA.EDU> Reply-To: ckp@grebyn.UUCP (Checkpoint Technologies) Organization: Grebyn Timesharing, Vienna, VA, USA Lines: 35 In article <34955@shemp.CS.UCLA.EDU> ravi@maui.cs.ucla.edu (T.M Ravi) writes: > >I am looking for information on DEC's Mass Storage Control Protocol (MSCP), >and their Mass Storage Subsystem. I am interested in how they provide a >logical interface which is device independent. Any information related to this >or pointers on how to obtain it would be appreciated. I've read the MSCP protocol documents and have written an MSCP disk driver (for a custom OS); however, that was a few years ago so all the details are foggy. I can't say much about anything besides the CPU's programming model for MSCP. Being device independent is pretty simple. SCSI does that too. The device is expected to appear as a linear array of 512-byte sectors numbered from 0 to the size of the device. The CPU knows nothing about tracks or cylinders, though with a command it can find out. The IO space contains a big total of two registers, the SA and the IP registers. The bulk of communications between the CPU and MSCP is via a communication region in memory. The CPU builds a request packet, "touches" the IP register to indicate there's a command; the MSCP interface reads the command from memory, performs it, and writes a reply packet into a different area describing how the operation went. There can be several packets outstanding, and the MSCP device may seek-optimize them. You can get the MSCP specs from Digital, but I don't know how hard that might be. DEC has been getting very secretive about programing info for some of their hardware, especially MSCP and TMSCP (MSCP for tape); but that's really the best place to get the documents. -- First comes the logo: C H E C K P O I N T T E C H N O L O G I E S / / \\ / / Then, the disclaimer: All expressed opinions are, indeed, opinions. \ / o Now for the witty part: I'm pink, therefore, I'm spam! \/