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