Requirements:

Android source tree (rowboat)

Linux kernel (2.6.37)

Ubuntu

adb

RIL (https://github.com/aferre/sierra-ril)

Beware: I did this work in Froyo (2.2) and I got to the point where I could start a ppp (Point to Point Protocol) but I couldn’t have a network access. I don’t know whether the bug came from Android or my work. I then decided to use Gingerbread (2.3.4), so the work here is targeting Ginger, but you could try it on Froyo as weel or any other version. If you got it working, I’d be glad to put your work here or link to it.

Intro

Google made it “easy” for vendors to integrate their modem into Android. Indeed, it would have been a pain if HTC, Samsung, … would have had to create a complete library and work on the low level system layers in Android. Everything one has to do to be able to use a modem (either with a 2G, 3G, or another access technology) is included in the directory /hardware/ril/ (provded that the java framework doesn’t have any bug, but if it does i’ll try to point them out).

Actually, apart from a few bug fixes in the RIL sources, from what I understand you’ll only have to modify the libreference-ril.c file. Google and the Android team provide a typical RIL (called libreference-ril) implementing the functions needed, and providing some kind of low level documentation (documentation in Android, for the system parts and not the application dev part, is really, REALLY, light).

In order to make it easier to compile and debug the RIL for the steps that are coming, i’ll put some tips and scripts.

Setup Android before building it

You should read this entire post before doing anything, as you’ll have to do a couple of things before actually building Android.

First of all, you need to add PPP support to the linux kernel. Here are the things you need to set:

• Device drivers
• network device support
• enable PPP support
• enable ppp suport for async serial line
• enable ppp support for sync serial line
• enable SLIP (TBD)
• Enable telephony support (TBD)
• USB support
• USB Modem (CDC ACM) support
• USB Serial Converter support

Also, in Gingerbread I am not able to get a USB/RS232 converter to be mounted as the system boots. So when booted, I just do a

insmod /sdcard/ftdi_sio.ko

to load the ftdi kernel module. I previously had to enable ftdi support in device drivers/usb support/usb serial converter/. I added it as a module, and after building it, moved it to the sdcard.

Building the ril

The first script will first compile the RIL with the Android build system, and push the library to the target using adb (so you need to be connected to your target with adb). Be carefull here: I spent a few days debugging a non working RIL because I didn’t use the Android build system to compile it. The system didn’t give me any error when building/using the RIL, but the RIL was indeed buggy as it didn’t output the messages in the good order, and was reseting every 15 seconds … I have to thank vrb (from rowboat IRC channel on irc.freenode.net): vrb, love ya.

During the development, I used to put the Android source tree in the directory /home/<whatever_your_session_name_is>/bin/gingerbread. The RIL provided here is on my github page.

#!/bin/sh
echo "Using defaults"
ANDSOURCES=~/bin
GINGER=$ANDSOURCES/gingerbread
SIERRA=~/sierra-ril
PRODUCT=beagleboard

cp $SIERRA/Android.mk $GINGER/hardware/ril/reference-ril/
cp $SIERRA/atchannel.c $GINGER/hardware/ril/reference-ril/
cp $SIERRA/atchannel.h $GINGER/hardware/ril/reference-ril/
cp $SIERRA/at_tok.c $GINGER/hardware/ril/reference-ril/
cp $SIERRA/at_tok.h $GINGER/hardware/ril/reference-ril/
cp $SIERRA/misc.c $GINGER/hardware/ril/reference-ril/
cp $SIERRA/misc.h $GINGER/hardware/ril/reference-ril/
cp $SIERRA/sierra-ril.c $GINGER/hardware/ril/reference-ril/

cd $ANDSOURCES/gingerbread/
source build/envsetup.sh
make clean
mm libreference-ril TARGET_PRODUCT=beagleboard -j8

adb push $GINGER/out/target/product/$PRODUCT/system/lib/libril.so /system/lib/
adb push $GINGER/out/target/product/$PRODUCT/system/lib/libreference-ril.so /system/lib/

Note that when pushing the new RIL to the target device, you can use it right away without having to reboot. Simply kill the rild process by using the ps command, finding out the rild PID (process identifier) and using the command kill <rild_PID>.

Fixing the base RIL

As I said the base RIL is buggy.

First, you need to explicitly set your modem speed in Android, so that you don’t have problems when talking to your device. You do this in the reference-ril.c file, located in ../hardware/ril/libreference-ril/. In the static void mainLoop function replace the following:

else if (s_device_path != NULL) {
                fd = open (s_device_path, O_RDWR);
                if ( fd >= 0 && !memcmp( s_device_path, "/dev/ttyS", 9 ) ) {
                    /* disable echo on serial ports */
                    struct termios  ios;
                    tcgetattr( fd, &ios );
                    ios.c_lflag = 0;  /* disable ECHO, ICANON, etc... */
			tcsetattr( fd, TCSANOW, &ios );
                }

by the following

else if (s_device_path != NULL) {
                fd = open (s_device_path, O_RDWR);
                if ( fd >= 0 && !memcmp( s_device_path, "/dev/ttyS", 9 ) ) {
                    /* disable echo on serial ports */
                    struct termios  ios;
                    tcgetattr( fd, &ios );
                    ios.c_lflag = 0;  /* disable ECHO, ICANON, etc... */
                    LOGI("Setting speed");
                   if( cfsetispeed( &ios, B115200) != 0 )
                       LOGE("Failed to set in speed");
                   if ( cfsetospeed( &ios, B115200) != 0 )
                       LOGE("Failed to set out speed");
			tcsetattr( fd, TCSANOW, &ios );
                }

In the file ril.cpp (../hardware/ril/libril/ril.cpp), you have to remove a couple of things. First, find this part:

// start listen socket
#if 0
    ret = socket_local_server (SOCKET_NAME_RIL,
            ANDROID_SOCKET_NAMESPACE_ABSTRACT, SOCK_STREAM);

    if (ret < 0) {
        LOGE("Unable to bind socket errno:%d", errno);
        exit (-1);
    }
    s_fdListen = ret;

#else
    s_fdListen = android_get_control_socket(SOCKET_NAME_RIL);
    if (s_fdListen < 0) {
        LOGE("Failed to get socket ‘" SOCKET_NAME_RIL "‘");
        exit(-1);
    }

    ret = listen(s_fdListen, 4);

    if (ret < 0) {
        LOGE("Failed to listen on control socket ‘%d‘: %s",
             s_fdListen, strerror(errno));
        exit(-1);
    }
#endif

and change #if 0 to #if 1, and also remove the #else. You should have this

  // start listen socket

#if 1
    ret = socket_local_server (SOCKET_NAME_RIL,
            ANDROID_SOCKET_NAMESPACE_ABSTRACT, SOCK_STREAM);

    if (ret < 0) {
        LOGE("Unable to bind socket errno:%d", errno);
        exit (-1);
    }
    s_fdListen = ret;

//#else
    s_fdListen = android_get_control_socket(SOCKET_NAME_RIL);
    if (s_fdListen < 0) {
        LOGE("Failed to get socket ‘" SOCKET_NAME_RIL "‘");
        exit(-1);
    }

    ret = listen(s_fdListen, 4);

    if (ret < 0) {
        LOGE("Failed to listen on control socket ‘%d‘: %s",
             s_fdListen, strerror(errno));
        exit(-1);
    }
#endif

Right below this part is another thing you need to change: the #if 1 to #if 0. This is to prevent the debug socket interface from being setup

In the file hardware/ril/rild/rild.c, change this part

/* special override when in the emulator */
 #if 1
 {
to
/* special override when in the emulator */
 #if 0
 {

Fixing Android

Now you have to make Android be aware that the modem is on whatever device (/dev/<something>) you put it on. I used a Sierra Wireless Q26 modem, with a USB and 2 RS232 interfaces (they will allow me not to use the AT commands software multiplexer). When connecting the modem with the USB interface, I have to add both the cdc_acm driver and the sierra wireless driver that are available in the linux kernel. The modem will then show up as a ttyACMx device node. The RIL needs this information to figure out where to send commands, and we’ll provide this information in the init.rc file located in the root directory of your Android system.

init.rc

What you need is to add or modify these lines:

loglevel 4

setprop ro.radio.noril no

setprop hw.nophone false

service ril-daemon /system/bin/rild -l /system/lib/libreference-ril.so -- -d /dev/ttyACM0
   socket rild stream 660 root radio
   socket rild-debug stream 660 radio system
   user root
   group radio cache inet misc audio vpn net_admin

service pppd_gprs /etc/ppp/init.gprs-pppd
   user root
   group radio cache inet misc
   disabled

The first line increases the debug level so that you can see at commands being sent and answered. Then, we tell Android it must use the RIL and after that, that it has a phone device.

The next part defines the ril-daemon service. You have to provide here the device node you’ll use, the ril library, and the groups allowed to use the daemon. Permissions are very important in Android, and you’ll see that there are a few things you’ll have to do to make it all work.

The last part defines the pppd_gprs service, which will allow you to get a data connection. Now, I have seen a few ways to get the data connection: using the Point to Point Protocol, which you will see here, using RMNET, a Qualcomm proprietary implementation.

ueventd.rc

You also need to set permissions for the device node. The RIL and all radio frequency related devices, daemons and libraries are in the radio group. So, at boot time or when you connect the modem, Android should auto magically set the correct permissions. This will be done in the file ueventd.rc in the root dir of Gingerbread. Note that this is only for Android 2.3 and above. With earlier versions, you need to add those permissions in a file called devices.c.

So in ueventd.rc, add the following, with /dev/ttyACM0 and/dev/ttyUSB0 pointing to whatever device nodes you want:

 /dev/ttyACM0  0660   radio      radio
 /dev/ttyUSB0  0660   radio      radio

From now on, you should be able to start the RIL successfully.

You’ll also have to set the init.gprs_pppd permission to 755 once you put it in its directory. Plus, to add it to the radio group, you’ll have to modify the file called property_service.c located in the Android source tree at ../system/core/init/property_service.c.

/*
 * White list of UID that are allowed to start/stop services.
 * Currently there are no user apps that require.
 */
struct {
    const char *service;
    unsigned int uid;
    unsigned int gid;
} control_perms[] = {
    { "dumpstate", AID_SHELL, AID_LOG },
    { "pppd_gprs", AID_RADIO, AID_LOG },
     {NULL, 0, 0 }
};

PPP files

For this part, you should go to Use PPP In Android.