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/*

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 * Per-frame timing-critical bit-banging.

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 *

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 * Shamelessly stolen from

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 *  http://code.google.com/p/tinkerit/source/browse/trunk/DmxSimple/DmxSimple.cpp

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 *

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 *  Copyright (c) 2008-2009 Peter Knight, Tinker.it!

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 *

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 * Consumes approx. 11 * 64 ~= 705 clock cycles

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 * Leaves the line idle (high) on return.

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 */

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void dmx_frame (volatile byte value)

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{

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  uint8_t bitCount, delCount;

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  __asm__ volatile (

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    "cli\n"

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    "ld __tmp_reg__,%a[dmxPort]\n"

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    "and __tmp_reg__,%[outMask]\n"

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    "st %a[dmxPort],__tmp_reg__\n"

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    "ldi %[bitCount],11\n" // 11 bit intervals per transmitted byte

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    "rjmp bitLoop%=\n"     // Delay 2 clock cycles.

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  "bitLoop%=:\n"\

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    "ldi %[delCount],%[delCountVal]\n"

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  "delLoop%=:\n"

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    "nop\n"

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    "dec %[delCount]\n"

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    "brne delLoop%=\n"

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    "ld __tmp_reg__,%a[dmxPort]\n"

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    "and __tmp_reg__,%[outMask]\n"

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    "sec\n"

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    "ror %[value]\n"

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    "brcc sendzero%=\n"

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    "or __tmp_reg__,%[outBit]\n"

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  "sendzero%=:\n"

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    "st %a[dmxPort],__tmp_reg__\n"

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    "dec %[bitCount]\n"

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    "brne bitLoop%=\n"

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    "sei\n"

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    :

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      [bitCount] "=&d" (bitCount),

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      [delCount] "=&d" (delCount)

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    :

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      [dmxPort] "e" (&DMX_PORT),

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      [outMask] "r" (~(1 << DMX_DATA)),

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      [outBit] "r" ((1 << DMX_DATA)),

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      [delCountVal] "M" (F_CPU/1000000-3),

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      [value] "r" (value)

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  );

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}