1 /*

     2  * Per-frame timing-critical bit-banging.

     3  *

     4  * Shamelessly stolen from

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

     6  *

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

     8  *

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

    10  * Leaves the line idle (high) on return.

    11  */

    12 void dmx_frame (volatile byte value)

    13 {

    14   uint8_t bitCount, delCount;

    15   __asm__ volatile (

    16     "cli\n"

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

    18     "and __tmp_reg__,%[outMask]\n"

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

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

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

    22   "bitLoop%=:\n"\

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

    24   "delLoop%=:\n"

    25     "nop\n"

    26     "dec %[delCount]\n"

    27     "brne delLoop%=\n"

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

    29     "and __tmp_reg__,%[outMask]\n"

    30     "sec\n"

    31     "ror %[value]\n"

    32     "brcc sendzero%=\n"

    33     "or __tmp_reg__,%[outBit]\n"

    34   "sendzero%=:\n"

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

    36     "dec %[bitCount]\n"

    37     "brne bitLoop%=\n"

    38     "sei\n"

    39     :

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

    41       [delCount] "=&d" (delCount)

    42     :

    43       [dmxPort] "e" (&DMX_PORT),

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

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

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

    47       [value] "r" (value)

    48   );

    49 }