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diff --git a/Documentation/input/devices/walkera0701.rst b/Documentation/input/devices/walkera0701.rst new file mode 100644 index 000000000000..2adda99ca717 --- /dev/null +++ b/Documentation/input/devices/walkera0701.rst @@ -0,0 +1,128 @@ +=========================== +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 + +---------+ +------+ + | | | | + --+ +------+ +--- + +Frame +----- + +:: + + SYNC , BIN1, OCT1, BIN2, OCT2 ... BIN24, OCT24, BIN25, next frame SYNC .. + +pulse length +------------ + +:: + + Binary values: Analog octal values: + + 288 uS Binary 0 318 uS 000 + 438 uS Binary 1 398 uS 001 + 478 uS 010 + 558 uS 011 + 638 uS 100 + 1306 uS SYNC 718 uS 101 + 798 uS 110 + 878 uS 111 + +24 bin+oct values + 1 bin value = 24*4+1 bits = 97 bits + +(Warning, pulses on ACK are inverted by transistor, irq is raised up on sync +to bin change or octal value to bin change). + +Binary data representations +--------------------------- + +One binary and octal value can be grouped to nibble. 24 nibbles + one binary +values can be sampled between sync pulses. + +Values for first four channels (analog joystick values) can be found in +first 10 nibbles. Analog value is represented by one sign bit and 9 bit +absolute binary value. (10 bits per channel). Next nibble is checksum for +first ten nibbles. + +Next nibbles 12 .. 21 represents four channels (not all channels can be +directly controlled from TX). Binary representations are the same as in first +four channels. In nibbles 22 and 23 is a special magic number. Nibble 24 is +checksum for nibbles 12..23. + +After last octal value for nibble 24 and next sync pulse one additional +binary value can be sampled. This bit and magic number is not used in +software driver. Some details about this magic numbers can be found in +Walkera_Wk-0701_PCM.pdf. + +Checksum calculation +-------------------- + +Summary of octal values in nibbles must be same as octal value in checksum +nibble (only first 3 bits are used). Binary value for checksum nibble is +calculated by sum of binary values in checked nibbles + sum of octal values +in checked nibbles divided by 8. Only bit 0 of this sum is used. |