Android - send HDMI CEC commands to TV - minix - libCEC

Question

i'm working on a Minix NEO X8-H (Android media center, 4.4.2) and i need to send HDMI-CEC command to TV: when my App receives a call i want to change automatically the TV Source to the Minix hdmi source.

Actually the Minix offer some options to enable HDMI-CEC and the media center software XBMC is reported to support CEC. But only in "receive mode" i guess: the user can command the Android device using TV remote. I want to work the opposite way. I browse XBMC's source code and i found very interesting code but do not know if it can be useful to me.

I found the serial device that get HDMI-CEC input commands

/dev/input/event7

The kernel references are placed at: "/sys/devices/virtual/input/input7/"

# cat /sys/devices/virtual/input/input7/name
cec_input

This is a part of dmesg log:

http://pastebin.com/raw.php?i=A5dE3qLu

<5>[    0.000000@0] Kernel command line: init=/init console=ttyS0,115200n8 no_console_suspend storage=5 cvbsdrv=0 vdaccfg=0xa007 logo=osd1,loaded,0x15100000,4k2ksmpte,full hdmimode=4k2ksmpte cvbsmode=576cvbs androidboot.firstboot=0 hdmitx=cec0
<4>[    0.000000@0] kernel get hdmimode form uboot is 4k2ksmpte
<4>[    0.000000@0] hdmitx: cec: Function List: disable, , , 
<4>[    0.000000@0] hdmitx: cec: HDMI aml_read_reg32(P_AO_DEBUG_REG0):0x0
<4>[    0.000000@0] hdmitx: cec: HDMI hdmi_cec_func_config:0x0
<4>[    1.392440@1] hdmitx: cec: CEC not ready
<4>[    4.872752@0] hdmitx: cec: CEC init
<4>[    4.876194@1] hdmitx: cec: CEC task process
<4>[    4.876398@0] hdmitx: cec: hdmitx_device->cec_init_ready:0x1

that proves the effective presence of HDMI-CEC built-in support.

I found libCEC and i managed to cross-compile it using Android NDK toolchain and i was able to install "libcec.so" and a demo client binary "cec-client" onto the Minix.

These are the build options:

asd@vm-ubuntu:~/Desktop/libcec/libcec-master/build$ cmake ..
-- Could NOT find PythonLibs (missing:  PYTHON_LIBRARIES PYTHON_INCLUDE_DIRS)
-- Could NOT find PythonLibs (missing:  PYTHON_LIBRARIES PYTHON_INCLUDE_DIRS)
-- Could NOT find PythonLibs (missing:  PYTHON_LIBRARIES PYTHON_INCLUDE_DIRS)
-- Could NOT find PythonLibs (missing:  PYTHON_LIBRARIES PYTHON_INCLUDE_DIRS)
-- Could NOT find SWIG (missing:  SWIG_EXECUTABLE SWIG_DIR)
-- Configured features:
-- Pulse-Eight CEC Adapter:                no
-- Pulse-Eight CEC Adapter detection:      no
-- lockdev support:                        no
-- xrandr support:                         no
-- Raspberry Pi support:                   no
-- TDA995x support:                        no
-- Exynos support:                         no
-- Python support:                         no
-- lib info: compiled on Linux-3.13.0-35-generic, features: P8_USB
-- Configuring done
-- Generating done
-- Build files have been written to: /home/asd/Desktop/libcec/libcec-master/build

I know that libcec works with an external hdmi-cec controller or, if build with Raspberry support feature it can runs smoothly on a raspi, using its integrated video controller.

If it can run on raspi it must be able to run on a Minix, i guess.

The cec-client was a demo client, developed to communicate with a serial interface and actually it can not communicate with /dev/input/evet7 because of some errors:

root@NEO-X8:/data # cec-client -t p -p 4 /dev/input/event7                    
== using device type 'playback device'
using HDMI port '4'
CEC Parser created - libCEC version 3.0.0
opening a connection to the CEC adapter...
DEBUG:   [               7]     Broadcast (F): osd name set to 'Broadcast'
ERROR:   [            3520]     error opening serial port '/dev/input/event7': Invalid argument
ERROR:   [            3521]     could not open a connection (try 1)
ERROR:   [            6355]     error opening serial port '/dev/input/event7': Too many open files
ERROR:   [            6355]     could not open a connection (try 2)
ERROR:   [            8243]     error opening serial port '/dev/input/event7': Too many open files
ERROR:   [            8243]     could not open a connection (try 3)
ERROR:   [            9501]     error opening serial port '/dev/input/event7': Too many open files
ERROR:   [            9501]     could not open a connection (try 4)
unable to open the device on port /dev/input/event7
NOTICE:  [           10506]     connection opened

But AFAIK Hdmi-CEC use a serial communication protocol using pin 13 of the HDMI connector so even if "cec-client" is a demo client it must be able to work properly! As you see there is a problem on locking the device or something similar.

Problems:

• it is possible to send CEC command via Android using Java?
• if not, anyone know how to adapt the libCEC/cec-client to work on Minix?

If Java way is not possible there are no problems: my own app is built using Qt and actually i'm already using a couple of native shared librare ".so"

Anyone has tips? How can accomplish that?

Answer 1

My two cents on the issue:

Chapter I: Compassion

I went through all the trouble you went, too, especially with libCEC, so I'd like to describe the only way I got any interaction going between an Android TV box and the TV connected to it with HDMI cable.

Chapter II: Cooking low and slow

Send a request for connected device's power status echo 0x40 0x8F > /sys/class/cec/cmd

To get the response, you can:

1. read the "registry" cat /sys/class/cec/dump_reg

2. wait and look for the response in logcat

// Example:
02-06 16:33:10.568  4012  4105 D CEC     : [cec_rx_loop]msg:04 90 00
02-06 16:33:10.570  4012  4105 D HdmiCecExtend: onCecMessageRx
02-06 16:33:10.657  4012  4012 W HDMI    : [1]:Unhandled cec command:<Report Power Status> src: 0, dst: 4, params: 00
02-06 16:33:10.762  4012  4104 D CEC     : [cec_send_message][4 -> 0]len:3, body:00 90 00 , result:success

Magic numbers (codes) explanation:

40 - Playback device #1
04 - TV device #1
On - 90 00
Off - 00 00 // in registry or no response at all in logcat

Other available codes can be constructed or read on Cec-O-Matic or amlogic.

Chapter III: New hope

I still have to try and get to Android's HdmiControlService but I still don't know how, probably through Java reflection. You can see HdmiCecExtend: onCecMessageRx so the API is available on the device, but you cannot use it in Android Studio, as far as I know, it's only available to Android TV vendors.

Will update if anything comes along.

Answer 2

First of all, very impressive reverse engineering work!

Secondly, I'm facing a similar issue (but with a non Minix product). Have you tried upgrading to a newer firmware, such as this one:

http://minixforum.com/threads/x8-x8-plus-x8-h-official-firmware-004a-not-for-x8-h-plus.5567/

I am suggesting this as a possible solution, because one of the issues it fixes is this:

Fixed HDMI-CEC multi devices issues

This means the device is not only a "slave", but also a "master" (i.e. can send commands to other hdmi devices).

Please note that as stated in the link, it is not intended for the plus version.

Good luck!