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B2G/RIL

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B2G RIL

This page contains information about B2G's interaction with the Radio Interface Layer of Android. The RIL provides access to the radio hardware, which is needed to send/receive calls, SMS messages, and other things that require interaction with a cell network.


  • B2G Dialer Test
    • Description

This program demonstrates how to communicate with the B2G RIL daemon, for dialing the phone, dealing with SMS, and other actions requiring access to the cell phone radio.

    • Goals

- Create patch to make android radio core not connect to rild socket - Figure out/find documentation for commands for ril events - Create function that will dial phone via socket calls - Create function that will wait for an SMS message (async) via sockets

  • Talking to the Radio
    • Low Level Access

Kernel access for specific phones are vendor specific, included in the phone's firmware distribution. To access these drivers, android uses the libril library. Information on libril and android's telephony architecture is available at

[[1]]

Source code for libril and rild is available in the B2G checkout as

glue/gonk/hardware/ril

    • Socket Access

In order to access libril, android uses an ipc socket interface to the rild daemon. The daemon simply creates a socket named "rild" and manages transfers of ipc parcels (http://developer.android.com/reference/android/os/Parcel.html) through it.

A sample emulator implementation of rild is available alongside the libril source code. Actual rild implementations for phones are proprietary and distributed by the vendor.

Due to wanting a single event source for dealing with events, the rild socket requires exclusive access from a single process. In a normal android installation, this would happen via the com.android.phone process. In order to make our own code talk to the socket, the current strategy is to change the socket name in the RIL.java file to something other than "rild" (since we can't recompile vendor specific rild).

    • Android Access

Android code specific to RIL communication is in

glue/gonk/frameworks/base/telephony/java/com/android/internal/telephony/RIL.java

The Java code communicates with the rild socket via the Binder IPC system, using objects known as Parcels. Parcels are simply flattened, serialized data structures. libbinder exists for C++ in glue/gonk/frameworks.

To access sockets via C, android uses libcutils, also available in glue/gonk/frameworks.

    • Parcel Formats

Parcels contain information about the transaction that they are a part of, as well as event data.

Event data will be one of the follow types:

- Void - No return - Int List - First int is the number of ints in the list, followed by the ints 

 - Byte 0x0c - uint32_t - number of ints in the packet
 - Byte 0x10 - uint32_t* - list of ints

- String - A single string (16-bit) 

 - Byte 0x0c - uint32_t - length of string
 - Byte 0x10 - wchar_t* - string of length specified

- Strings - An array of strings (16-bit) 

 - Byte 0x0c - uint32_t - number of strings
 - Byte 0x10 - Strings - strings in format listed for single string (size + string)

- Custom Struct - A set of different types specific to the message (SMS messages, call lists, etc...)

      • RIL Parcel - Process -> rild

Each RIL Socket Write has the following format:

- Byte 0x00 - uint32_t - Header (Size of Following Parcel) 

 - PARCEL BEGINS AFTER THIS FIELD

- Byte 0x04 - uint32_t - RIL Event ID (IDs available in glue/gonk/hardware/ril/include/telephony/ril.h) - Byte 0x08 - uint32_t - Packet Serial Number (Used to track send/receive order) - Byte 0x0c - void* - Event Data

      • RIL Parcel - rild -> Process (solicited reply)

Each RIL Socket Read (for a solicited response) has the following format:

- Byte 0x00 - uint32_t - Header (Size of Following Parcel) 

 - PARCEL BEGINS AFTER THIS FIELD

- Byte 0x04 - uint32_t - 0 (To signify it is a reply to a previously sent solicited request) - Byte 0x08 - uint32_t - Packet Serial Number (Used to track send/receive order) - Byte 0x0c - void* - Event Data

It is expected that the client maintains a list of previously made solicited requests to match the replies to, via the serial field.

The expectations of each RIL event are outlined in the comments for the fields in the ril.h file.

      • RIL Parcel - rild -> Process (unsolicited event)

Each RIL Socket Read (for a solicited response) has the following format:

- Byte 0x00 - uint32_t - Header (Size of Following Parcel) 

 - PARCEL BEGINS AFTER THIS FIELD

- Byte 0x04 - uint32_t - 1 (To signify it is a reply to a previously sent solicited request) - Byte 0x08 - uint32_t - RIL Event ID (IDs available in glue/gonk/hardware/ril/include/telephony/ril.h) - Byte 0x0c - void* - Event Data

The client responds (as needed) to unsolicited events by sending a solicited event, which follows the outline mentioned above.

The expectations of each RIL event are outlined in the comments for the fields in the ril.h file.

  • Phone Workflow
    • Initialization

The initialization step is required to turn the radio on. - Program connects to rild socket - Radio: UNSOL_RESPONSE_RADIO_STATE_CHANGED with radio status - Program: SCREEN_STATE to TRUE - Program: RADIO_POWER (Turns radio on, if radio status is RADIO_STATE_OFF)

    • Service Status Update

- Radio: UNSOL_RESPONSE_NETWORK_STATE_CHANGED - Program: OPERATOR - Program: REGISTRATION_STATE - Program: GPRS_REGISTRATION_STATE

    • Dialing

- Go through initialization and Service Status Update steps - Program: DIAL (Just dialing doesn't work)

    • Hanging Up

- Android app usually sends REQUEST_HANGUP_FOREGROUND_RESUME_BACKGROUND - Continually checks GET_CURRENT_CALLS, which may error the first time around? [[2]]

    • Call Receive
    • SMS Receive

- Radio: UNSOL_RESPONSE_NEW_SMS - Program: RIL_REQUEST_SMS_ACKNOWLEDGE

  • Gecko Design

For preliminary design documentation of WebTelephony/WebAPI, see [[3]]

    • Design Overview

The RIL communications system will consist events in the context of 3 threads, as well as a socket proxy daemon:

- The IPC Thread, where IO to the Radio Socket will happen - A JS Worker thread, where low level telephony support (parsing 

 parcels to/from socket, dealing with GSM/CDMA/SIP and SIM card
 commands, etc...) will be implemented

- The Main Gecko Thread, where the Telephony DOM will expose high 

 level commands to the navigator.phone object.
    • Radio Base Class - IO Thread

The Radio Base Class declares the basic communication function signatures for radios, as well as managing a queue of binary blobs coming from and going to the radio. It contains no knowledge of the blob structure, just blob length and the blobs themselves. This means we can push the Parcel (or whatever serialization method we decide to use) creation up into the Telephone class, keeping Radio in its own thread to deal with I/O.

    • Radio JS Worker Thread

The Radio Implementation class will handle

- Providing an interface to phone status (Network Name, Signal 

 Strength, Current Calls, Radio Events, etc...)

- Creating and Managing data in flight from/to the radio

Radio communication at the parcel level happens in the worker thread, which then queues the serialized binary blobs to the Radio I/O thread. It also reads information sent from the radio, to trigger events like incoming calls.

    • Telephony DOM

The Telephone class is responsible for exposing high level functions to Javascript (Dial, Hangup, SMS, etc...). More information on this is available as part of the WebTelephony project.

  • Utilities and Tips
    • Building

- Set the path of your local Android NDK and B2G, i.e. export 

 NDK=/opt/android-ndk-r6b

- Run scripts/android_env.sh - cmake . - make

    • Debugging

The command "logcat -b radio" in the android shell will print all radio messages

Tracing the packet formats going between com.android.phone and the rild socket can be achieved by watching strace on the rild process. Due to the fact that rild spawns multiple threads, this should be done with the fork option, i.e.

strace -p XXXX -f

To trigger events that happens from outside the network, the rild-debug socket is provided by rild. This socket responds to a different set of commands, in order to inject RIL events into the ril core. It's mainly used for testing new ril implementations.

    • Tools
      • ADB convenience

To automate some of the common tasks involved with resetting processes on the phone, watching logs, etc... I've made a few different custom targets in the CMake file. These can be run using

make [target_name]

in the out-of-source build directory. The targets are:

- adbpush - Push b2g-dialer-test binary to phone. - adbdial - Run b2g-dialer-test. Currently does not work. - adbrwmount - Remount / and /system as rw for duration of session 

 (i.e. until next reboot)

- adbjavaon/adbjavaoff - With the patch to the android code, java now 

 tries to connect to /dev/socket/rild2 instead of /dev/socket/rild.
 This allows us to connect to rild via our own process when needed,
 but also means we can symlink rild2 to rild when we want to watch
 how android interacts with something (useful for analyzing code
 flow). adbjavaon creates the symlink (at which point b2g-dialer-test
 binary will fail due to needing exclusing socket access). adbjavaoff
 will remove the symlink and kill the android phone process, causing
 it to drop its connection to the socket.
      • b2g-dialer-forward

b2g-dialer-forward is a utility for forwarding the rild unix socket to the network, so that developers can work on API. adb forward is available to unix sockets, but due to the account access check for 'radio' by rild, we need to establish the network port as root, then communicate with the socket as rild.

b2g-dialer-forward connects the rild unix socket to port 5555 on the phone. This can then be forwarded to the desktop using adb forward with the tcp protocol.

As an example, the dialer.py test script uses this utility to talk to the phone daemon without having to actually run on the phone.

    • Relevant Websites

- [[4][Hooking up Android to a GSM radio on the BeagleBoard]] - [[5][libril Documentation]] - [[6][Small thread on ril stuff]] - [[7][Android Radio Interface Layer]] - [[8][Android Telephony Stack]]



Relevant Bugs

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