Documentation/input/devices/walkera0701.rst

Source file repositories/reference/linux-study-clean/Documentation/input/devices/walkera0701.rst

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Documentation/input/devices/walkera0701.rst
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Support Tooling And Documentation
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Support Tooling And Documentation: documentation
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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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===========================
Walkera WK-0701 transmitter
===========================

Walkera WK-0701 transmitter is supplied with a ready to fly Walkera
helicopters such as HM36, HM37, HM60. The walkera0701 module enables to use
this transmitter as joystick

Devel homepage and download:
http://zub.fei.tuke.sk/walkera-wk0701/

or use cogito:
cg-clone http://zub.fei.tuke.sk/GIT/walkera0701-joystick


Connecting to PC
================

At back side of transmitter S-video connector can be found. Modulation
pulses from processor to HF part can be found at pin 2 of this connector,
pin 3 is GND. Between pin 3 and CPU 5k6 resistor can be found. To get
modulation pulses to PC, signal pulses must be amplified.

Cable: (walkera TX to parport)

Walkera WK-0701 TX S-VIDEO connector::

 (back side of TX)
     __   __              S-video:                                  canon25
    /  |_|  \             pin 2 (signal)              NPN           parport
   / O 4 3 O \            pin 3 (GND)        LED        ________________  10 ACK
  ( O 2   1 O )                                         | C
   \   ___   /      2 ________________________|\|_____|/
    | [___] |                                 |/|   B |\
     -------        3 __________________________________|________________ 25 GND
                                                          E

I use green LED and BC109 NPN transistor.

Software
========

Build kernel with walkera0701 module. Module walkera0701 need exclusive
access to parport, modules like lp must be unloaded before loading
walkera0701 module, check dmesg for error messages. Connect TX to PC by
cable and run jstest /dev/input/js0 to see values from TX. If no value can
be changed by TX "joystick", check output from /proc/interrupts. Value for
(usually irq7) parport must increase if TX is on.



Technical details
=================

Driver use interrupt from parport ACK input bit to measure pulse length
using hrtimers.

Frame format:
Based on walkera WK-0701 PCM Format description by Shaul Eizikovich.
(downloaded from http://www.smartpropoplus.com/Docs/Walkera_Wk-0701_PCM.pdf)

Signal pulses
-------------

::

                     (ANALOG)
      SYNC      BIN   OCT
    +---------+      +------+
    |         |      |      |

Annotation

Implementation Notes