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

[Anand Arumugam]

On Mon, Dec 17, 2012 at 2:02 AM, Ritesh Harjani <ritesh.harjani at gmail.com>wrote:

> 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.
>

Did you try 'strace'?
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