[LinuxBIOS] OLPC Keyboard/System Controller ENE KB3920

[Jim Gettys]

On Tue, 2006-03-14 at 08:13 -0600, Bari Ari wrote:
> Jim,
> 
> I see from the OLPC Wiki
> 
> http://wiki.laptop.org/wiki/Hardware_specification
> 
> that the ENE KB3920
> 
> http://www.ene.com.tw/
> 
> is to be used for keyboard scan and system management.
> 
> Are there plans to keep the code for this open as well?
> 
> Many types of these controllers share memory space with the flash that 
> stores the BIOS. The KB3920 data sheet is not available from the ENE 
> website. Do you know if this device has enough flash, OTP or mask ROM to 
> hold all of it's own code or will it share with the system BIOS?

I think the part may not have been released yet;  so you get the part
number for now; or maybe it is just some variant of an existing part.  I
don't know the exact situation and will have to ask Quanta.

It isn't clear to me if we should release the code (at least without
some thought) to this part.

IIRC, the flash in which LinuxBIOS is getting stored is interfaced via
this controller and is a serial flash part; possible sizes are 4
megabits and 8 megabits.  We save something like $.3 to $.5 if we can
use the 4 megabit part.  Right now, we are carrying the 8 megabit
version on the BOM.

Here's what I'm paranoid about: that the serial flash rom in which
LinuxBIOS  and bootloader is stored gets overwritten, and the laptop is
no longer a laptop, but an expensive brick.  I particularly worry about
someone writing a worm that manages to do this, and that
thousands/millions of machines all over the world are unrecoverable.
The logistics of repair are impossible.  I will ask Mark Foster about
how that flash gets write enabled; if we can absolutely in hardware
inhibit write to the boot flash, then I get much less worried.  I've
sent him mail asking.

I do want the bootloader sequence in this flash to be able to load a
second copy of itself out of the regular main flash so that later
versions can be installed safely (with appropriate checksum checking).
I don't want the situation we had on the iPAQ where you could possibly
"brick" the unit when updating the bootloader.  The iPAQ valhalla we had
(you could send us a bricked iPAQ and we'd eventually reflash it via
jtag and return it) was a PITA, and not feasible for OLPC.  We have to
ensure boot and restore is absolutely bulletproof.
					- Jim

-- 
Jim Gettys
One Laptop Per Child