129 lines
4 KiB
ReStructuredText
Executable file
129 lines
4 KiB
ReStructuredText
Executable file
===========================
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Walkera WK-0701 transmitter
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===========================
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Walkera WK-0701 transmitter is supplied with a ready to fly Walkera
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helicopters such as HM36, HM37, HM60. The walkera0701 module enables to use
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this transmitter as joystick
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Devel homepage and download:
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http://zub.fei.tuke.sk/walkera-wk0701/
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or use cogito:
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cg-clone http://zub.fei.tuke.sk/GIT/walkera0701-joystick
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Connecting to PC
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================
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At back side of transmitter S-video connector can be found. Modulation
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pulses from processor to HF part can be found at pin 2 of this connector,
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pin 3 is GND. Between pin 3 and CPU 5k6 resistor can be found. To get
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modulation pulses to PC, signal pulses must be amplified.
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Cable: (walkera TX to parport)
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Walkera WK-0701 TX S-VIDEO connector::
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(back side of TX)
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__ __ S-video: canon25
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/ |_| \ pin 2 (signal) NPN parport
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/ O 4 3 O \ pin 3 (GND) LED ________________ 10 ACK
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( O 2 1 O ) | C
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\ ___ / 2 ________________________|\|_____|/
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| [___] | |/| B |\
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------- 3 __________________________________|________________ 25 GND
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E
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I use green LED and BC109 NPN transistor.
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Software
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========
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Build kernel with walkera0701 module. Module walkera0701 need exclusive
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access to parport, modules like lp must be unloaded before loading
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walkera0701 module, check dmesg for error messages. Connect TX to PC by
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cable and run jstest /dev/input/js0 to see values from TX. If no value can
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be changed by TX "joystick", check output from /proc/interrupts. Value for
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(usually irq7) parport must increase if TX is on.
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Technical details
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=================
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Driver use interrupt from parport ACK input bit to measure pulse length
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using hrtimers.
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Frame format:
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Based on walkera WK-0701 PCM Format description by Shaul Eizikovich.
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(downloaded from http://www.smartpropoplus.com/Docs/Walkera_Wk-0701_PCM.pdf)
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Signal pulses
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-------------
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::
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(ANALOG)
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SYNC BIN OCT
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+---------+ +------+
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| | | |
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--+ +------+ +---
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Frame
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-----
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::
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SYNC , BIN1, OCT1, BIN2, OCT2 ... BIN24, OCT24, BIN25, next frame SYNC ..
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pulse length
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------------
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::
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Binary values: Analog octal values:
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288 uS Binary 0 318 uS 000
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438 uS Binary 1 398 uS 001
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478 uS 010
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558 uS 011
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638 uS 100
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1306 uS SYNC 718 uS 101
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798 uS 110
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878 uS 111
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24 bin+oct values + 1 bin value = 24*4+1 bits = 97 bits
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(Warning, pulses on ACK are inverted by transistor, irq is raised up on sync
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to bin change or octal value to bin change).
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Binary data representations
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---------------------------
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One binary and octal value can be grouped to nibble. 24 nibbles + one binary
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values can be sampled between sync pulses.
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Values for first four channels (analog joystick values) can be found in
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first 10 nibbles. Analog value is represented by one sign bit and 9 bit
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absolute binary value. (10 bits per channel). Next nibble is checksum for
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first ten nibbles.
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Next nibbles 12 .. 21 represents four channels (not all channels can be
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directly controlled from TX). Binary representations are the same as in first
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four channels. In nibbles 22 and 23 is a special magic number. Nibble 24 is
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checksum for nibbles 12..23.
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After last octal value for nibble 24 and next sync pulse one additional
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binary value can be sampled. This bit and magic number is not used in
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software driver. Some details about this magic numbers can be found in
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Walkera_Wk-0701_PCM.pdf.
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Checksum calculation
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--------------------
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Summary of octal values in nibbles must be same as octal value in checksum
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nibble (only first 3 bits are used). Binary value for checksum nibble is
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calculated by sum of binary values in checked nibbles + sum of octal values
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in checked nibbles divided by 8. Only bit 0 of this sum is used.
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