how does this command(at+cfun=1,1) works?

[Ritesh Harjani]

Hi Yann,


On Mon, Dec 17, 2012 at 3:12 PM, Yann Droneaud <ydroneaud at opteya.com> wrote:

> Le lundi 17 décembre 2012 à 12:41 +0530, Ritesh Harjani a écrit :
> > Hi Everyone,
> >
> > When this command (at+cfun=1,1) is executed on phone, it does a
> > reboot. I want to know which and how this command calls the kernel
> > level functions.
> > I googled this, but seems like all the data explains only about AT
> > command and not as to how this reboot process is done.
> >
>
> The kernel alone is not responsible of interpreting Hayes commands (AT).
>
> According to ETSI TS 100 916 V7.4.0 (1999-11) Technical Specification
> Digital cellular telecommunications system (Phase 2+); AT command set
> for GSM Mobile Equipment (ME) (GSM 07.07 version 7.4.0 Release 1998),
> Section 8.2 Set phone functionality +CFUN (found through by
> http://wiki.openmoko.org/wiki/Hardware:AT_Commands ), this command
> (AT+CFUN=1,1) is one of the command a "baseband" must implement.
>
> >And this command is asking for a reboot. So what you describe seems more
> >likely to be a hardware problem.
>

On Android phones(some of them) there are essentially two processors.
The *Application
Processor (AP)* where your Android operating system (AOS) and user
interface (UI) lives, and the *Baseband/Cellular Processor (BP/CP)* where
all the GSM and other high-tech communication magic happens, including the
modem we wish to communicate with.
Here, AP and BP communicates via UART (serial line), USB, SPI or through
shared RAM and/or a combination of these. Therefore there will always be
some path directly accessible from the outside that we should be able to
use to communicate directly with the BP.

So, what I am asking for is not any hardware problem. What I have figured
out that, this command (at+cun=1,1) calls for sysrq reset which does a
emergency restart.
But, I wanted to know the exact path that it follows before calling Sysrq
key.

Thank you
Ritesh



>
> Regards.
>
> --
> Yann Droneaud
> OPTEYA
>
>
>
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