cctech Digest, Vol 21, Issue 22

[Mark Matlock]

On Mar 23, 2016, at 12:00 PM, cctech-request at classiccmp.org wrote:

> Message: 2
> Date: Tue, 22 Mar 2016 16:34:01 +0100
> From: Mattis Lind <mattislind at gmail.com>
> To: "General Discussion: On-Topic and Off-Topic Posts"
> 	<cctalk at classiccmp.org>
> Subject: RSX11S
> Message-ID:
> 	<CABr82SKAPr=Ck92GKPmog9S64GSe2D2Z47A7yS-mFpAeKcGptg at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
> 
> While archiving a bunch of old 8 inch disks I found disks that apparently
> contain an old RSX11S system. I think it has been used in some kind of
> railroad CTC system.
> 
> https://dl.dropboxusercontent.com/u/96935524/Datormusuem/PDP11RX01DISKS/DISK4.RAW
> 
> It is possible to boot this image in SimH (when setting CPU type to 11/03,
> 11/23 (F11), 11/34 or 11/73 (J11) )
> 
> I get this:
> 
> sim> b rx0
> XDT: 18
> XDT>g
> RSX-11S V02 BL18
> 
> 
> DEVICE TT01: NOT IN CONFIGURATION
> DEVICE FT00: NOT IN CONFIGURATION
>> a
> MCR -- 1
>> b
> MCR -- 1
>> ccc
> MCR -- 1
>> 
> 
> 
> So first there is a XDT> prompt. By pressing g or p it starts RSX11S. But
> it seems to be possible to do other things. Commands like "s" and "l" do
> stuff "x" causes:
> 
> XDT>x
> 
> SYSTEM CRASH AT LOCATION 025276
> 
> REGISTERS
> 
> R0=000000 R1=177170 R2=003403 R3=157000
> 
> R4=012422 R5=000002 SP=157004 PS=000340
> 
> SYSTEM STACK DUMP
> 
> LOCATION CONTENTS
> 
>  157004   157150
> 
> HALT instruction, PC: 000572 (MOVB #15,R2)
> sim>
> 
> I understand that RSX11S is a scaled down version of RSX11M. An embedded
> RTOS of that day. But what kind of commands are possible at the XDT and
> MCR(?) prompts. I am a little bit curious to understand more about the
> system that it has been running.
> 
> 
> /Mattis

Mattis,
    A good description of what is possible in RSX11S can be found in the manual:

http://bitsavers.trailing-edge.com/pdf/dec/pdp11/rsx11/RSX11S_V4.2_Jul85/AA-2874F-TC_RSX-11S_4.2_Sysgen_Jul85.pdf

    Because you got the MCR - 1 (Illegal Function) response I think basic MCR must have been included in the system. The XDT> is the eXecutive Debugging Tool and is similar to ODT. The X is a command to do a crash dump.

   There are not many MCR commands available in RSX11S, but one that you should try is TAL which if it was included in the system sysgen will display all the installed tasks and their status, ATL shows which tasks are active. RUN task name will execute a task that is installed.
The most interesting thing that you might find in the system, if it was included is a task called RSDV1H which displays a live picture of the memory organization and system operation similar to RMD on a RSX11M or M+ system.

   RSX11S was designed to be a memory resident real-time priority driven multitasking system. It is booted from a disk but really doesn't have a file system unless it is included in the sysgen and then it only does block I/O type operations.  Nonresident tasks can be loaded by a task loader if that capability is sysgened in.

   This all sounds pretty limiting and it is but still RSX11S can do a lot when needed. Over 30 years ago, I helped create a system that read data from 8 commodity exchanges & a news wire feed in various formats, then sent DECnet data packets to 10 PDP-11/23s running RSX11S. The 11/23s each had 20 VT100s hung off each one (using DLV11Js and DZV11s) with each commodity trader getting customized screens of data in real-time. The goal was to get data to the traders faster than any other commercial service. News headlines scrolled across the bottom of the VT100 and the trader could request specific stories which were stored in a RMS-11 Indexed file back on the main server which was an 11/44 run RSX11M. The RSX11S systems had no disk and were downloaded the OS over the leased data line running at 9600 baud (fast for the day). The 11/23s ran re-entrant Macro-11 code in 256 Kbytes of RAM (OS, programs, & DECnet).

Best Regards,
Mark