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Re: Linux on a VR4111.

To: linux-mips@fnet.fr
Subject: Re: Linux on a VR4111.
From: Warner Losh <imp@village.org>
Date: Fri, 13 Nov 1998 20:34:27 -0700
In-reply-to: Your message of "Fri, 13 Nov 1998 22:03:18 EST." <XFMail.981113220318.sbutts@purdue.edu>
References: <XFMail.981113220318.sbutts@purdue.edu>
In message <XFMail.981113220318.sbutts@purdue.edu> Steve Butts writes:
:    I just joined the list so I dunno if this topic has been
: discussed yet or not.  I was wondering if anyone here knew if it
: would be possible to run Linux on a NEC MIPS VR4111?  Mainly to
: convert a WinCE system to a usuable portable network computer
: running Linux.  I haven't been able to find much information on the
: processors besides a simple Dhrystone benchmark so I don't even know
: how fast these chips are and if it would be even worth the effort.

Yes.  People have looked into this.  I have looked into this.  You
might check out the japanese nec site.  They have the datasheets and
user manuals for the Vr4111 (as well as other 41xx machines).  You'll
find that almost all of what you need to know in that cpu user's
manual as this part is highly integrated.

The cache lines and sizes are differently determined than other mips
processors.  There will need to write lots of drivers, as they aren't
pc compatible.

Finally, the biggest barrier to entry is that it is hard to boot these
devices.  they boot from rom, which is hard to replace.  so there
needs to be some kind of vector.  I think that for the MobilePro 4x0
that I have it will be possible to leverage off the touch screen
driver to "overwrite" the memory that WinCE has setup.  With this sort
of thing, you'll likely find that memory is extremely tight.  It may
be possible to run off a flash card which may help some.  It may also
be possible to create BOOT ROMS, but I've been unable to find any chip
that has the same pinouts as the mask roms that are used in the mobile
pro.  It may be possible to puzzle out the pinouts of the rom
daughter card so that another one can fabricated that takes, eg, flash
roms.

I've not had time to work on this lately, as things at work have been
insane.  The MobilePro 4x0 has a Vr4101 which is fairly similar to the
Vr4111, but with a smaller cache, and more non-standard hardware (the
serial ports on the Vr4111 are 16450 compatible, while the 4101 has at
least one that is specific to the 4101.  Oh, the 4101 has SIR while
the 4111 has FIR, and there are at least two versions of the Vr4111
which have slightly different IR registers).

Warner

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