Re: Neo900 - finally a successor of N900
 

Yes, exactly. Also keep in mind that SYS_BOOT only defines where from ROMBOOT loads xloader aka MLO. The latter then loads uBoot from arbitrary storage - depending on what's coded into xloader. Finally uBoot loads the kernel and tells kernel where is /-fs. So even without any control over SYS_BOOT[5] the natural method to do "multiboot" is to have uBoot (as well as xloader) loaded from NAND and uBoot then lets user decide where kernel and system should get fetched from. In case xloader in NAND is not found, the ROMBOOT will fall through to next source in boot sequence
So SYS_BOOT[5]=1 is only needed to recover from a broken xloader/uBoot in OneNAND, by booting from either USB, UART3 (HackerBus) or MMC1. While normal changing of boot device (and thus kernel and system) is done in uBoot which can have all the protection against attacks you could think of. And since OneNAND is first in normal boot sequence, if you locked your device there's no way for an attacker to bypass that security in uBoot, except of unlocking the device again which means disassemble and solder which can't get done without losing RAM content. So your encrypted filesystem is secure when your device has a lockscreen enabled :-) The less concerned user would keep the battery lid hallswitch connected to SYS_BOOT[5] to allow forcing of e.g. USB (xloader) boot in case some mishap messed up e.g. uBoot. For added safety you would want your system to erase from RAM any cryptokeys for your encrypted filesystems as soon as a battery lid removal gets detected on a screenlocked device.

cheers
/j

Re: Neo900 - finally a successor of N900
 

I hadn't thought of that obvious risk. It sounds good then that SYS_BOOT5 is not easily accessible without removing the whole board and maybe soldering something first.

Why use the hallswitch for that purpose? If we have the Hackerbus, could one of its pins be jumper-able to SYS_BOOT5 instead? Basically so that test automation is easier, like if having to bisect a uBoot bug or something. Not my idea, but its something I've heard from a Linaro developer while visiting ARM so probably has wisdom in it.

Thanks!

p.s. this is also a defence against supply-chain interdiction - the paranoid end-user should be able to re-flash MLO/uBoot - even if the ones in flash are not 'broken' they may be considered untrusted.

Re: Neo900 - finally a successor of N900
 

As I mentioned in the announcements thread
http://talk.maemo.org/showthread.php?p=1493994
we have promising candidates for the flash LEDs, which were one of the remaining few problem spots.

Now the question is what color temperature to choose. Unfortunately, it seems that we don't have much information about the original LEDs. Would anyone happen to be able to measure or estimate the color temperature of the N900 flash LEDs ?

My guess would be "higher is better" (for a flash), but then that's not really my domain, and the experts seem to have a variety of opinions on this, too:
http://www.flashlightuniversity.com/...r-temperature/

Wikipedia suggests 5500 K:
https://en.wikipedia.org/wiki/Flash_(photography)

In any case, we should try to match the color of the original N900 flash.

Worst case, we can always try a side-by-side comparison, but I hope there's a more exact way.

Suggestions ?
- Werner

Re: Neo900 - finally a successor of N900
 

Does anybody have RX-51 schematics, and do they help any?

Thank you. Best wishes.

Re: Neo900 - finally a successor of N900
 

No idea about anybody, but google has it :P

http://plan9.stanleylieber.com/hardw...schematics.pdf

Re: Neo900 - finally a successor of N900
 

also see http://wiki.maemo.org/N900_Hardware_Schematic :)
/j

ps: ooops, stale links

Re: Neo900 - finally a successor of N900
 

The ones I know unfortunately don't contain part numbers.

Also
http://www.electronicproducts.com/No...e_text-90.aspx
knows the price has nothing else to say but "Primary Camera Flash - High Intensity White".

A search for that would lead us here
http://www.carclo-optics.com/optic-1...ntensity-white
But no, that one is rather far off :)

- Werner

Re: Neo900 - finally a successor of N900
 

I just did a quick & dirty test (rather unscientific) by taking a direct photograph of the n900's LED with a DSLR and setting white balance manually in rawtherapee (you basically specify a region that is supposed to be white and it gives you the color temperature then). I get about 5600 Kelvin, so 5500 does seem reasonable. Please keep in mind that this is in no way a calibrated measurement, but it should give you an idea.

Re: Neo900 - finally a successor of N900
 

Great, thanks a lot !

I currently have my eyes set on the L130-5780002011001 with 5700 K and a minimum CRI of 80%. CRI is something new I found:
https://en.wikipedia.org/wiki/Color_rendering_index

Of course, two parameters are still a very course approximation of the actual spectrum. But you'd probably need serious lab equipment to determine that. (A comparison between two LEDs would be easier, though, since any systematic errors of the test setup would affect both measurements in the same way. Joerg suggested using a prism. You'd still need a proper lab setup, though, if only to make sure the geometry doesn't change between tests.)

- Werner

Re: Neo900 - finally a successor of N900
 

There's a nice instruction on how making a spectrometer out of cardbox and a DVD-R as a diffraction grating:
https://publiclab.org/sites/default/...ni-spec3.8.pdf
Using a good camera, it seems possible to get surprisingly good results from this:
https://publiclab.org/notes/cfastie/...ometer-testing

So, if you're a bit into that stuff, it could be fun to build one (I feel a bit tempted to do this myself now :D ).

But the most pragmatic solution probably is this: get a colorchecker chart, take a raw image on the n900 with fcamera using LED illumination, compare using a standard white balance setting, pick the LED closest to the original one. Just from the spectrum, the effects of different LEDs could be a bit hard to predict, because of the color filter array on the sensor and its transmission function.