negative addresses

[== M. Yuhara ==]

In article <2393 at uvacs.CS.VIRGINIA.EDU>, wulf at uvacs.CS.VIRGINIA.EDU (Bill Wulf) writes:
> Has anyone ever seen a machine with "negative addresses", that is, one
> where the address space is -2**31..2**31-1 rather than 0..2*32-1??

Yes, yes.
TRON chip deals an address as an signed integer.
On TRONCHIP32, -2**31..-1 is called Shared-semi-Space (SS) which is shared
among processes. 0..2**31-1 is called Unshared-semi-Space (US) which is
independent among processes.
(You can think of SS as System's Space, and US as User's Space).

TRON chip architecture is designed to be extensible from 32 bit address space
through 48 (TRONCHIP48) to 64 bit address space (TRONCHIP64).

If you think SS is 2**31..2*32-1, you will have difficulty when you
extend address space. But if you think it is signed, address space can
be extended naturally.

		-2**63	+---------+
		   /	|         |
		 /	|         |
		/	|         |
	       /	|         |
-2GB+---------+ -2**31  |         |
    |  SS     |         |   SS    |
    |         |         |         |  <-- Some system parameters stay here.
  0 +=========+       0 +=========+      (such as reset vector.)
    |         |         |         |
    |  US     |         |         |
+2GB+---------+ 2**31-1 |   US    |
	       \    	|	  |
		\	|         |
		 \	|         |
		   \	|         |
		2**63-1	+---------+




-- 
Artifitial Intelligence Division
Fujitsu Laboratories LTD., Kawasaki, Japan.
Masanobu YUHARA
kddlab!yuhara%flab.flab.fujitsu.junet at uunet.UU.NET