Q: Is there any guidelines document on 3G/4G modem integration with the iMX platforms running Android Lollipop versions ?
A: Generally speaking, porting documents on 3G/4G should be provided by manufacture, For different 3G/4G module, porting steps are also distinct.The following steps are for ZTE 3G on android jb 4.2.2, as a reference:
(1) linux USB driver
In linux kernel, we should select GSM module in USB driver path.
(2)Communication port for 3G
After linux booting normally, you can find some communation port at path /dev/, like ttyUSB0,ttyUSB1,ttyUSB2...
These tty ports are for AT commands & data transmitting, but which one is for data , or which one is for AT command, we should have to ask manufacture or get information for them.
3G manufacture will give the script to you, if not, ask for it.
3G manufacture will give you the library to replace original one in android.
(5)Add service for 3G in init.rc file according their documents
---As an example, let us see steps for ZTE 3G(CDMA)
** Replace original file with libreference-ril.so file that ZTE released.
**Copy init.gprs-pppd file to system/etc/ppp directory
**Modify init..rc like following:
service ril-daemon /system/bin/rild -l /system/lib/libreference-ril.so -- -d /dev/ttyUSB2 -u /dev/ttyUSB0
socket rild stream 660 root radio
socket rild-debug stream 660 radio system
socket rild-ppp stream 660 radio system
group radio cache inet misc audio sdcard_rw log
service pppd_gprs /etc/ppp/init.gprs-pppd
group radio cache inet misc