1===========================
2Walkera WK-0701 transmitter
3===========================
4
5Walkera WK-0701 transmitter is supplied with a ready to fly Walkera
6helicopters such as HM36, HM37, HM60. The walkera0701 module enables to use
7this transmitter as joystick
8
9Devel homepage and download:
10http://zub.fei.tuke.sk/walkera-wk0701/
11
12or use cogito:
13cg-clone http://zub.fei.tuke.sk/GIT/walkera0701-joystick
14
15
16Connecting to PC
17================
18
19At back side of transmitter S-video connector can be found. Modulation
20pulses from processor to HF part can be found at pin 2 of this connector,
21pin 3 is GND. Between pin 3 and CPU 5k6 resistor can be found. To get
22modulation pulses to PC, signal pulses must be amplified.
23
24Cable: (walkera TX to parport)
25
26Walkera WK-0701 TX S-VIDEO connector::
27
28 (back side of TX)
29     __   __              S-video:                                  canon25
30    /  |_|  \             pin 2 (signal)              NPN           parport
31   / O 4 3 O \            pin 3 (GND)        LED        ________________  10 ACK
32  ( O 2   1 O )                                         | C
33   \   ___   /      2 ________________________|\|_____|/
34    | [___] |                                 |/|   B |\
35     -------        3 __________________________________|________________ 25 GND
36                                                          E
37
38I use green LED and BC109 NPN transistor.
39
40Software
41========
42
43Build kernel with walkera0701 module. Module walkera0701 need exclusive
44access to parport, modules like lp must be unloaded before loading
45walkera0701 module, check dmesg for error messages. Connect TX to PC by
46cable and run jstest /dev/input/js0 to see values from TX. If no value can
47be changed by TX "joystick", check output from /proc/interrupts. Value for
48(usually irq7) parport must increase if TX is on.
49
50
51
52Technical details
53=================
54
55Driver use interrupt from parport ACK input bit to measure pulse length
56using hrtimers.
57
58Frame format:
59Based on walkera WK-0701 PCM Format description by Shaul Eizikovich.
60(downloaded from http://www.smartpropoplus.com/Docs/Walkera_Wk-0701_PCM.pdf)
61
62Signal pulses
63-------------
64
65::
66
67                     (ANALOG)
68      SYNC      BIN   OCT
69    +---------+      +------+
70    |         |      |      |
71  --+         +------+      +---
72
73Frame
74-----
75
76::
77
78 SYNC , BIN1, OCT1, BIN2, OCT2 ... BIN24, OCT24, BIN25, next frame SYNC ..
79
80pulse length
81------------
82
83::
84
85   Binary values:		Analog octal values:
86
87   288 uS Binary 0		318 uS       000
88   438 uS Binary 1		398 uS       001
89				478 uS       010
90				558 uS       011
91				638 uS       100
92  1306 uS SYNC			718 uS       101
93				798 uS       110
94				878 uS       111
95
9624 bin+oct values + 1 bin value = 24*4+1 bits  = 97 bits
97
98(Warning, pulses on ACK are inverted by transistor, irq is raised up on sync
99to bin change or octal value to bin change).
100
101Binary data representations
102---------------------------
103
104One binary and octal value can be grouped to nibble. 24 nibbles + one binary
105values can be sampled between sync pulses.
106
107Values for first four channels (analog joystick values) can be found in
108first 10 nibbles. Analog value is represented by one sign bit and 9 bit
109absolute binary value. (10 bits per channel). Next nibble is checksum for
110first ten nibbles.
111
112Next nibbles 12 .. 21 represents four channels (not all channels can be
113directly controlled from TX). Binary representations are the same as in first
114four channels. In nibbles 22 and 23 is a special magic number. Nibble 24 is
115checksum for nibbles 12..23.
116
117After last octal value for nibble 24 and next sync pulse one additional
118binary value can be sampled. This bit and magic number is not used in
119software driver. Some details about this magic numbers can be found in
120Walkera_Wk-0701_PCM.pdf.
121
122Checksum calculation
123--------------------
124
125Summary of octal values in nibbles must be same as octal value in checksum
126nibble (only first 3 bits are used). Binary value for checksum nibble is
127calculated by sum of binary values in checked nibbles + sum of octal values
128in checked nibbles divided by 8. Only bit 0 of this sum is used.
129