Path: utzoo!telly!ddsw1!lll-winken!uunet!tut.cis.ohio-state.edu!DECWRL.DEC.COM!dan%jeremy.DEC
From: dan%jeremy.DEC@DECWRL.DEC.COM (Dan Frommer)
Newsgroups: gnu.gcc
Subject: Targeting GCC to a 16-bit'er
Message-ID: <8810050730.AA29328@decwrl.dec.com>
Date: 5 Oct 88 13:30:00 GMT
Sender: daemon@tut.cis.ohio-state.edu
Distribution: gnu
Organization: GNUs Not Usenet
Lines: 27

Attached is the "Q" processor spec. I'm interested in hosting GCC under
VAX/VMS, while targeting the code to the 16-bit Q. Is this feasable?
Are there limitations on targeting GCC's output to a 16-bit machine?
How hard is it to adapt the machine description files to a new target?

Dan

                      "Q" Processor Description
                      -------------------------

     The "Q" processor is a 16 bit micro-controller used as an on-chip
control processor, which also has a 16-bit address space.

     It has 8 general purpose registers, a stack pointer, and  several
other  control  registers  (The  SP & PC are not part of the GPRs).  A
single addressing mode is available:  Base Register +  Offset.   Small
(5-bit)  constants can be used as literals in arithmetic instructions,
and a Load Immediate instruction can load a  register  with  a  single
word  constant.   Memory  can  only  be referenced using word (16-bit)
addresses.  Least significant bits have lower addresses.

     The instruction set includes various integer arithmetic & logical
instructions.    but   no   multiply/divide.   No  condition  code  is
available, and test reg+branch is done using single  instructions.   A
carry bit is available to enable multiple precision arithmetic.

     The  stack  is  used  for  push/pop  register  instructions,  and
call/return.