up			     up
    IN           OUT		left,	right
         down			    down

  pickup   C    hangup		enter, backspace, escape
    1      2      3			1, 2, 3
    4      5      6			4, 5, 6,
    7      8      9			7, 8, 9,
    *      0      #			*, 0, #,

|[]   [][]   [][]   [][]   in   |[][]
|[] M [][] D [][] : [][]   out  |[][]
                          store

NEW REP         SU MO TU WE TH FR SA

[] [] [] [] [] [] [] [] [] [] [] []
[] [] [] [] [] [] [] [] [] [] [] []

'8' :  Generic 7 segment digit with individual addressable segments

Reduced capability 7 segment digit, when segments are hard wired together.
'1' : 2 segments digit only able to produce a 1.
'e' : Most significant day of the month digit,
      able to produce at least 1 2 3.
'M' : Most significant minute digit,
      able to produce at least 0 1 2 3 4 5.

Icons or pictograms:
'.' : For example like AM, PM, SU, a 'dot' .. or other single segment
  elements.

   get_icons    Read, returns a set of available icons.
   hide_icon    Write, hide the element by writing the icon name.
   show_icon    Write, display the element by writing the icon name.

   map_seg7	Read/Write, the 7 segments char set, common for all
		yealink phones. (see map_to_7segment.h)

   ringtone	Write, upload binary representation of a ringtone,
		see yealink.c. status EXPERIMENTAL due to potential
		races between async. and sync usb calls.

Reading /sys/../lineX will return the format string with its current value.

  Example::

    cat ./line3
    888888888888
    Linux Rocks!

Writing to /sys/../lineX will set the corresponding LCD line.

 - Excess characters are ignored.
 - If less characters are written than allowed, the remaining digits are
   unchanged.
 - The tab '\t'and '\n' char does not overwrite the original content.
 - Writing a space to an icon will always hide its content.

  Example::

    date +"%m.%e.%k:%M"  | sed 's/^0/ /' > ./line1

  Will update the LCD with the current date & time.


get_icons

Writing to these files will update the state of the icon.
Only one icon at a time can be updated.

If an icon is also on a ./lineX the corresponding value is
updated with the first letter of the icon.

  Example - light up the store icon::

    echo -n "STORE" > ./show_icon

    cat ./line1
    18.e8.M8.88...188
		  S

  Example - sound the ringtone for 10 seconds::

    echo -n RINGTONE > /sys/..../show_icon
    sleep 10
    echo -n RINGTONE > /sys/..../hide_icon


Sound features
==============

Sound is supported by the ALSA driver: snd_usb_audio

One 16-bit channel with sample and playback rates of 8000 Hz is the practical
limit of the device.

  Example - recording test::

    arecord -v -d 10 -r 8000 -f S16_LE -t wav  foobar.wav

  Example - playback test::

    aplay foobar.wav


Troubleshooting
===============

:Q: Module yealink compiled and installed without any problem but phone
    is not initialized and does not react to any actions.
:A: If you see something like:
    hiddev0: USB HID v1.00 Device [Yealink Network Technology Ltd. VOIP USB Phone
    in dmesg, it means that the hid driver has grabbed the device first. Try to
    load module yealink before any other usb hid driver. Please see the
    instructions provided by your distribution on module configuration.

:Q: Phone is working now (displays version and accepts keypad input) but I can't
    find the sysfs files.
:A: The sysfs files are located on the particular usb endpoint. On most
    distributions you can do: "find /sys/ -name get_icons" for a hint.


Credits & Acknowledgments
=========================

  - Olivier Vandorpe, for starting the usbb2k-api project doing much of
    the reverse engineering.
  - Martin Diehl, for pointing out how to handle USB memory allocation.
  - Dmitry Torokhov, for the numerous code reviews and suggestions.