🚀 go-pugleaf

>From the recent discussion on CTCA's, I have the impression that you
>write a program that specifies the (virtual on CMS) addresses of the
>coupled CTCA's as channel device addresses and then tramsmits data from
>one to the other by means of an I/O program similar to one you would
>write for a DASD (disk).

        Yes.  Except that you would not have to do any SEEKs :-)

>                 ... I thought that instructions like RDD (Read Direct)       ,
>WRD (Write Direct) and SIGP (Signal Processor) would be used in a CTCA
>program.

        No ... SIO (Start I/O), TIO (Test I/O), and cousins.
READ/WRITE DIRECT use an 8-bit path,  only ONE path at that,  not
4096 or 8192 or 65536 possible addresses as with normal 370 I/O.
You want to go the Start-I/O route,  which means you'll need to learn
to write "channel programs".  But I think you'll find that channelized
I/O is better in many respects.

>I have a System/370 Reference Summary, Fourth Edition, November 1976.
>Is it too out-of-date to be reliable?

        It IS out of date,  but hang on to it!  After version 4 of that
reference,  they removed mention of certain virtual control bits,  which
are only meaningful in a virtual control register of a virtual machine.
The reference now deals only with real hardware,  I believe.

>                                     I know that the CMS nucleus, whose
>layout is described by the macro NUCON, occupies the low end of memory
>in the virtual machine.

        Actually,  CMS lives in hign memory,  usually a DCSS  (virtual
ROM)  beyond your machine's virtual RAM.

>         In that case, where are the Fixed Storage Locations, beginning
>with IPL PSW, IPL CCW1, IPL CCW2 etc. ...

        Those are in the addresses listed in your reference.  You can
do a  CP DISP vaddr  to examine them,  or a  CP STORE vaddr value(s)
to change them;  be careful!  REXX provides the STORAGE function.
In ASSEMBLEr programs,  you can refer to any virtual address you like.

 Rick Troth <TROTH@RICEVM1.RICE.EDU> ------------- Rice ONCS VM Systems Support