ZTE 3G module not responding to picocom

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My tablet (a Renesas-dual A9 w/ Android 2.3) has a ZTE-MF216 3G module onboard, 
perfectly functional for my data connections, but when I try to access the same 
on /dev/ttyUSB0 through picocom (cross-complied for ARM using Sourcery G++ 
Lite) it doesn't respond to commands, though the terminal connection looks 
correctly established:

------------------------
# dmesg
...
<6>option 1-1.1:1.0: GSM modem (1-port) converter detected
<6>usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB0
<6>option 1-1.1:1.1: GSM modem (1-port) converter detected
<6>usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB1
<6>option 1-1.1:1.2: GSM modem (1-port) converter detected
<6>usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB2
<6>option 1-1.1:1.3: GSM modem (1-port) converter detected
<6>usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB3
# 
# picocom --b 115200 /dev/ttyUSB0
picocom v1.6

port is        : /dev/ttyUSB0
flowcontrol    : none
baudrate is    : 115200
parity is      : none
databits are   : 8
escape is      : C-a
local echo is  : no
noinit is      : no
noreset is     : no
nolock is      : no
send_cmd is    : sz -vv
receive_cmd is : rz -vv
imap is        : 
omap is        : 
emap is        : crcrlf,delbs,

Terminal ready
------------------------

It stays there forever, with no feeback, no echo of the AT commands I try to 
type, neither I can exit with the escape commands... I need to switch off the 
3G module (from System Setting) to exit from the terminal.

Anything that I'm doing wrong? 

I'm pretty sure it's not a picocom issue... but I hope someone can help. Thanks.

Original issue reported on code.google.com by ffum...@googlemail.com on 2 Mar 2012 at 5:17

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Probably not a picocom issue. I leave it open in case somebody can help

Original comment by nick.pat...@gmail.com on 7 Mar 2012 at 7:13

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perhabs you should try /dev/ttyUSB1 or higher. Many usb 3G modems use different 
device files for Data and AT control commands.

Original comment by jannik.w...@googlemail.com on 11 May 2012 at 1:04

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[deleted comment]

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I made some partial progress, using picocom "-i" option (no port init), but 
this is what I get if I simply type A + T + Z + <enter> afters starting 
picocom: 

root@android:/ # picocom -i -f h -b 115200  /dev/ttyUSB3     
picocom v1.6

port is        : /dev/ttyUSB3
flowcontrol    : RTS/CTS
baudrate is    : 115200
parity is      : none
databits are   : 8
escape is      : C-a
local echo is  : no
noinit is      : yes
noreset is     : no
nolock is      : no
send_cmd is    : sz -vv
receive_cmd is : rz -vv
imap is        :
omap is        :
emap is        : crcrlf,delbs,

Terminal ready
AAAAAAAAAAAAAAAAAAATATATATATATZATZATZATZATZATZATZATZATZATZATZATZATZATZATZATZATZA
TZATZATZATZATZATZATZATZATZ

ERROR

ATZ

OK

ATZ

OK

ATZ

OK 

Single characters, as well as the entire command are repeated several times. 
But, at least I get the 'OK' back, sometimes. What could be happening here? Any 
idea?

Original comment by ffum...@googlemail.com on 29 May 2013 at 8:26