Pandora questions

[Chuck Robey-5]

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I bought me a nice new Pandora, and in the next 6 weeks before it arrives, I
want to get a bunch of questions answered dealing with me trying to do a ARMv7A
OpenBSD port.

My pandora hasn't been delivered yet, but I'm coming up with questions, some I'd
like to bounce of folks here.  I don't begin coding until my pandora gets
delivered, but I can do the research right now).  The first ones that hit me
regard some differences I've noted with the Cortex-A8, versus maybe an Arm6 (?)
 The Cortex-A8 has that 2 level security thing (they call it TrustZone), one
processor being secure, the other one being insecure (I think that's how you
refer to it).  This hasn't anything whatever to do with the ordinary split
between user-level and system-level, and beyond that, the split apparently
continues all the way out to peripherals.  Things like only code in the secure
processors can access secure peripherals.  Well, the question is, is there any
place in OpenBSD for TrustZone features?  That question not only asks whether
it's been used yet, it also asks if there is even any contemplated way that such
a feature *could* be used in OpenBSD.  I need to consider this, if I'm going to
seriously try to port the OpenBSD code to use the ARMv7A (same as Cortex-A8).  I
figure most of the differences I'm going to hit against are going to be more
obvious to me, just look how it's been done before (maybe for the Xscale in the
Sharp Zaurus) and see what possible changes might be available for me to use.
The trouble with TrustZone is, I know its not been done for any other palmtop I
ever heard of, so I don't have much idea how TrustZone might get used for
OpenBSD for ARMv7A.

I know another thing, that the BeagleBoard is based on precisely the same chip
(including all of the available modules that are in it, like the DSP stuff in
the Neon) as the Pandora.  I get the odea that the BeagleBoard might be the
perfect, cheap ($150 versus Pandora's $330) development platform.  I think, from
what I've read so far, that the only major differences are the LCD display and
chiclet qwerty keyboard that're in the Pandora.  So, if OpenBSD brings in the
Pandora, I think it'd be the same as saying it's bringing in the BeagleBoard.

What might the OpenBSD port be called?  Just a ARMv7A version of the OpenBSD/Arm
port?  Or, call it OpenBSD/Cortex-A8?  Or, refer to the hardware/software (like
callling it OpenBSD/Pandora? (or OpenBSD/BeagleBoard)?  I'm horrible at names,
I'd appreciate it if someone with better taste than I chose the name.

I'd like to discuss the Xscale's use of their memory controller.  I've not done
any work in VM before, and I have a question regarding the fact that, according
to the Xscale memory manager's tech manual, the replacement policy of the MM is
RoundRobin.  That seems incredibly odd to me, when LRU seems both the obvious
way to choose memory area replacement, and pretty simple to implement.  So, it's
seems to me more than a little likely that I just read the manual wrong.  I need
to know what's right, because I saw references to the same "round robin" in the
Cortex-A8 tech manual, so I wanted to know if round robin might be used by
OpenBSD?  I won't be mad if you just tell me that I read it all completely
wrong, better to know that than for me to go make some huge mistake in trying to
do the code for the Cortex-A8.

If you need for me to drag out references about this, I could do that, easily in
the Cortex (I have the manual pdf right here) and I wouildn't have too hard a
time getting the tech ref manual for the Xscale (I hope Intel hasn't pulled it
off their website!)  You just search for round robin, it's right here in black &
white.
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

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[Leif Lindholm-2]

Hi Chuck,

> The trouble with TrustZone is, I know its not been done for any other
> palmtop I
> ever heard of, so I don't have much idea how TrustZone might get used for
> OpenBSD for ARMv7A.

There is a (recently released) document about TrustZone available at:
http://infocenter.arm.com/help/topic/com.arm.doc.prd29-genc-009424c/index.html

My understanding it that this would not be the intended use of the
TrustZone features - although that does not necessarily mean they couldn't
be used for it.

Also, I think there is a "high security" version of the OMAP3530 that
actually implements useful TrustZone support, but that the one used on the
beagleboard for example does not really implement any of the hardware
features (i.e. Secure only memory) that would be required to actually gain
any additional security.

Regards,

Leif