Replied: Fri, 30 Sep 88 02:27:16 -0700
Date:  Thu, 29 Sep 88 12:59:22 PDT
From: Carl Lowenstein <cdl@mplvax.nosc.mil>
Message-Id:  <8809291959.AA09749@mplvax>
To: casey@CS.UCLA.EDU
Subject: how to tell a tm11

Newsgroups: comp.bugs.2bsd
In-Reply-To: <16291@shemp.CS.UCLA.EDU>
Organization: U.C. San Diego, Marine Physical Laboratory
Cc: cdl
Status: R

In article <16291@shemp.CS.UCLA.EDU> you write:

>  The problem is that the TS and the TM share the same CSR address
>(0172520), but the *standard* TS CSR is only two words long:
>
>	/*
>	 * TS11 controller registers
>	 */
>	struct tsdevice {
>		u_short	tsdb;		/* data buffer */
>		u_short	tssr;		/* status register */
>	};
>
>and the TM CSR is seven words long:
>
>	/*
>	 * TM11 controller registers
>	 */
>	struct tmdevice {
>		u_short	tmer;		/* error register, per drive */
>		u_short	tmcs;		/* control-status register */
>		short	tmbc;		/* byte/frame count */
>		caddr_t	tmba;		/* address */
>		short	tmdb;		/* data buffer */
>		short	tmrd;		/* read lines */
>		short	tmmr;		/* maintenance register */
>	};

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
Thanks to networked computers, I got hold of my RT11 sources without
having to leave this chair.  DEC tells the difference between TS11 and
TM11 with the following PDP11 assembly language (paraphrased):
(this is DEC-flavor not unix-flavor assembly language)

;;;;;;;;;;;;;;;;;;
	MOV	#MTCSR, R0		; point to control-status
	MOV	#1000, 2(R0)		; try to select unit 2
	BIT	#1000, 2(R0)		;  did it work?
	BNE	GOOD			; yes, it is a TM11
BAD:					; no, it isn't
	. . .
GOOD:
;;;;;;;;;;;;;;;;;;

I would take a first cut at translating this into C as:

	TMADDR->tmcs = 01000;		/* try to select unit 2 */
	if (TMADDR->tmcs & 01000) {
		/* do tm11 things */
	} else {
		/* do ts11 things */
	}
/* note that selecting unit 2 is a benign thing to do even if you have
    only one TM11 drive.  The controller can select up to 8 drives
    even if they are not present.  Of course, the non-existent drive
    doesn't report that it is ready. */

		carl

	carl lowenstein		marine physical lab	u.c. san diego
	{decvax|ucbvax}	!ucsd!mplvax!cdl