about UART on Nexus S

[PaulK]

Le vendredi 30 décembre 2011 à 09:38 +0800, 俞强 a écrit :
> Hi guys,
>     I make a UART line
> from http://trac.osuosl.org/trac/replicant/wiki/NexusSBootloader, but
> it doesn't work at all, then I swap Rx(D-) and Tx(D+), and it works,
> you make sure the table is right ?
> UART to USB board
> output
> resistor
> microUSB
> connector(s)
> name(s)
> microUSB wire
> color
> N/A
> 150K Ohm
> ID and GND
> ID not wired (the
> 5th connector
> that is unused),
> GND is black
> 3.3V
> N/A
> V+
> red
> GND
> N/A
> GND
> black
> Rx
> N/A
> D-
> white
> Tx
> N/A
> D+
> green

Hi! I have just tested a few minutes ago and I confirm this is working
very well. Perhaps you should check that you're using 3.3V and not 5V.

I am now working with a protoboard, which is quite a good idea as there
is no risk of naked-wires overlapping.

> btw, a few days ago I made a decision to write a opensource bootloader
> for Nexus S, then I found you project, and I'm interesting, so I want
> to do something for this great project, I think NS's bootloader is a
> good begin.

That's really amazing! The original idea was to use u-boot as first
bootloader (replacing the Samsung Primitive Bootloader, as they call
it), since u-boot has support for the SOC (s5pc110) but with the UART
output, we figured out that the board is e-fused, which means that the
bootloaders are signed (we know that from the s5pc110 datasheet). 

As a result, it's not possible to run u-boot as primitive bootloader.
Though, some enthusiastic Galaxy S (which is also s5pc110) users decided
to try to write a bootloader that permits to unbrick a bricked device. 
All of this is in
http://trac.osuosl.org/trac/replicant/wiki/NexusSBootloader#Linksofinterest

It's anyway not a replacement for the first bootloader but software that
will be chainloaded. As in Replicant, we care about freedom, we didn't
really see the point of having a free bootloader chainloaded by the same
remaining non-free ones. 

If you're still interested, I think you should get in touch with the
hummingbird-hibl authors and try to make it work on Nexus S.