Re: Assembler Clarification

Hi Ron,

I'm no wizard, but I like to dabble with assembler.

> It looks to me like one of the first things a program does in setting up
> it's own environment  is tell the CPU where to put the registers?  Are do the registers actually
> reside in memory?  Does each program get it's own set of registers? Gee that would make >context  changes  really easy..

You're only saving a *copy* of the current contents of the registers,
and this is only necessary, in the case where your program has been
called by another program, i.e. the O.S., when your program starts
running.

So when you save them with some variant of the ST(ore), STM( store
multiple) command, the saved copies *are* in memory.   The registers
themselves are part of the CPU hardware, not the memory hardware
(unlike many microcontrollers, like the PIC, where the "registers" are
really just memory addresses).

By changing the ARCHMODE config variable, Hercules can emulate three
different architectures :

1) S/370

  All of the "old" O.S'.s  we're running run S/370 mode  (** VM380
runs in ESA/390 mode ... )

#2009-09-11 22:30:00
ibm/370/princOps/GA22-7000-4_370_Principles_Of_Operation_Sep75.pdf
http://bitsavers.org/pdf/ibm/370/princOps/GA22-7000-4_370_Principles_Of_Operation_Sep75.pdf

#2009-09-11 22:29:00
ibm/370/princOps/GA22-7000-0_370_Principles_Of_Operation_Jun70.pdf
http://bitsavers.org/pdf/ibm/370/princOps/GA22-7000-0_370_Principles_Of_Operation_Jun70.pdf

Although  ESA/390,  Z/arch(ESAME)  won't be applicable when running
Turnkey MVS (as it runs in ARCHMODE  S/370).   You *can* run ARCHMODE
ESA/390, Z/arch (ESAME) on the "bare metal" though (no O.S.  just
using raw assembler).

I started a wiki on "bare metal" programming :
http://hercules-bare-metal.wikispaces.com/

ESA / 390
http://publibz.boulder.ibm.com/epubs/pdf/dz9ar008.pdf

Z/arch
http://publibz.boulder.ibm.com/epubs/pdf/dz9zr007.pdf

Zarch Summary / Reference Card
http://publibz.boulder.ibm.com/epubs/pdf/dz9zs005.pdf