arch/mach selection guidelines ?

["Galit Heller" <Galit dot Heller at nsc dot com>]

We are now creating gcc and binutils ports for National Semiconductor's
CR16C, CR16CPlus and CRX processors. These processors are members of
NS's CompactRISC family.

We have currently got one ELF machine identifier for the CompactRISC
family - EM_CR, which is used in the CR16C binutils port code.

The differences between the other CompactRISC processors and the CR16C
vary - some have a slightly different microarchitecture, e.g.
the CR16CPlus can access greater memory area, and some have a very
different instruction set, e.g. the CRX.

The question is twofold:

1. What are the guidelines for requesting a new separate ELF machine code
   for a processor ?

2. What are the guidelines for distinction between architecture and machine,
   i.e. how to decide whether to define two processors as two machs of the
   same archs or as two different archs ?

 It seems that in the ELF specification the terms machine and architecture
 are used interchangeably: the e_machine designates the architecture.
 However, in bfd there is a distinction between architecture and machine.
 What is the exact distinction and the relationship beween the bfd terms
 and the ELF terms, if any ?

Thanks,
Galit.