Re: mapping 36 bit physical addresses into 32 bit virtual

From: Maciej W. Rozycki (
Date: Wed Oct 16 2002 - 06:59:17 EST

On Wed, 16 Oct 2002, jw schultz wrote:

> OK. I guess i'm wrong. It may be that the hardware was
> locked into 32bit mode. The development period was a couple
> of years so we were running on essentially 89-90 tech with a
> faster clock.

 I'm not sure if you can lock a MIPS system into the 32-bit mode at all,
certainly not the processor -- it always runs with 64-bit operations
enabled when in the kernel mode (for the user and supervisor modes it's
selectable), though you may disable 64-bit addressing. A system may be
incapable of 64-bit operation if its system controller doesn't support
doubleword transfers on the host bus, but I'm not sure if it's possible to
force an R4k CPU to only use 32-bit transfers for cache fills and
writebacks. Probably not. So that's really the matter of software only.

+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+        e-mail:, PGP key available        +

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