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
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