On Mon, Dec 17, 2012 at 2:02 AM, Ritesh Harjani [off-list ref]wrote:

Hi Yann,


On Mon, Dec 17, 2012 at 3:12 PM, Yann Droneaud [off-list ref]wrote:

quoted

Le lundi 17 d?cembre 2012 ? 12:41 +0530, Ritesh Harjani a ?crit :

quoted

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.

quoted

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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