GTA04 Block V4

Ian Stirling OpenMoko at
Tue Aug 26 15:55:54 CEST 2008

Andy Green wrote:
> Hash: SHA1
> Somebody in the thread at some point said:
> | Andy Green wrote:
> |> Hash: SHA1
> |>
> |> Somebody in the thread at some point said:
> |>
> |> |> Really USB host is very "usable" and flexible for these tasks.
> |>
> |> | It mandates a microcontroller, USB and programming,
> |>
> |> So what?
> |
> | For some things - switches and buttons - it's a complication beyond just
> | jamming an I2C peripheral on there.
> Is that even true?  You still need a button <-> I2C device.  Then you
> might as well have a USB <-> button device and so not need to open the
> case -- and get power coming cleanly.  And your button / whatever works
> on a laptop or desktop PC.

Sorry for the delay in responding.

I'm absolutely not talking about uses where an external button would be 
any use.

This is - for example - to add an internal capacitive touch-slider to 
the case, so that the phone can sense finger position adjacent to the 

I have a prototype of this - but it's useless as a product as there is 
no way to connect it sensibly.

This is simply using a I2C-capacitive sensor chip - with 
absolutely no programming.

> |> | and can't do wakeup well.
> |>
> |> Citation needed.
> |
> | To clarify - as I understand it the likely power draw required for the
> | SC* to be awake enough to do USB suspend negotiations is rather high.
> | Plus it'd require a 5V source alive all the time.
> What's an SC*?

The hardware SoC inside the GTA04.

I am absolutely not suggesting this as an external interface, that would 
be utterly insane. This is an internal device only to the phone, that 
would be entirely useless not attached to the phone in a replacement case.

This was based on the assumption that the existing debug connector was 
staying - I was proposing a cheaper, less fragile and with cables 
available from stock online cheaply ($5) that would also be of use for 
internal expansion.

Using the external USB for this purpose makes any replacement case much, 
much harder, as it's got to instead of merely being a replacement back 
or front (or in some applications an internal fitment to the case) be an 
entire case, with a plug going into the side of the phone, a USB hub or 
switch inside, a USB socket, ...

> If all your device is doing is a button, you can take it down during
> suspend and re-enumerate it on resume.  Otherwise USB specifies clearly
> about max suspend current, 500uA.

USB suspend may specify that - as I understand the likely configuration 
of the SoC in the GTA04 - it will not support wake from suspend in the 
lowest power configurations.

Unfortunately, I don't have a datasheet as samsung restrict it, and I 
don't yet have an appropriate looking website yet.

> | 20 way 0.5mm FPC connectors are available off-the-shelf inexpensively.
> | This would make it useful for expansion, in addition to its primary
> | purpose, in a way that the existing one is not.
> It's wrongheaded.  Use a standard interface that already exists.  This
> week I tore my debug flat cable, they are evil compared to standard and
> robust USB connector.  I will definitely be agitating that we forget
> about any kind of nonstandard internal connector.

That particular flat cable is especially fragile, not that any are 
especially robust.

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