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1 #LyX 1.6.4 created this file. For more info see http://www.lyx.org/
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2 \lyxformat 345
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3 \begin_document
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4 \begin_header
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5 \textclass article
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6 \use_default_options true
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28 \secnumdepth 3
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29 \tocdepth 3
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30 \paragraph_separation indent
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31 \defskip medskip
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32 \quotes_language english
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33 \papercolumns 1
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34 \papersides 1
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35 \paperpagestyle default
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36 \tracking_changes false
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37 \output_changes false
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38 \author ""
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39 \end_header
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40
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41 \begin_body
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42
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43 \begin_layout Title
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44 Multi-Voice Audio Playback
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45 \end_layout
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46
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47 \begin_layout Author
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48 Laurel Pardue, Robert McIntyre
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49 \end_layout
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50
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51 \begin_layout Section*
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52 Micro-Architecture
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53 \end_layout
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54
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55 \begin_layout Subsection*
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56 A quick summary of our system
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57 \end_layout
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58
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59 \begin_layout Standard
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60 The audio data (
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61 \begin_inset Quotes eld
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62 \end_inset
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63
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64 samples
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65 \begin_inset Quotes erd
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66 \end_inset
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67
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68 ) start in the memory, but are soon pulled into action by the DMA (direct
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69 memory access).
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70 The DMA sends the samples to a chain of 0 or more
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71 \emph on
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72 soft-cores
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73 \emph default
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74 , where they are transformed according to the soft-cores' algorithms.
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75 After running the gauntlet of soft-cores, the samples flow first to a buffering
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76 FIFO, and finally to a
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77 \emph on
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78 mixer
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79 \emph default
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80 , which sends the samples off to be played by speakers of stored in a file.
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81 \end_layout
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82
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83 \begin_layout Subsection*
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84 A more detailed look a our system
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85 \end_layout
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86
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87 \begin_layout Standard
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88 Our audio pipeline starts its life with whatever music we want to play already
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89 in memory.
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90 The music has multiple tracks, or
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91 \begin_inset Quotes eld
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92 \end_inset
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93
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94 voices,
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95 \begin_inset Quotes erd
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96 \end_inset
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97
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98 which we arrange on the memory in contiguous sequences.
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99 Therefore, each voice starts at its own start-address, and continues on
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100 for as long as it needs.
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101 We cap each voice with an end-of-file marker.
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102 We make every voice the same length to simplify timing issues, even though
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103 that might mean that there is a lot of wasted space in the form of dead
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104 areas with no sound.
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105 \end_layout
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106
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107 \begin_layout Standard
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108 When the processing starts, the DMA reads in each voice and sends the audio
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109 data (
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110 \begin_inset Quotes eld
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111 \end_inset
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112
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113 samples
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114 \begin_inset Quotes erd
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115 \end_inset
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116
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117 ) off to a chain of soft-cores.
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118 The DMA knows to which chain the samples should be forwarded by looking
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119 up the samples' voice in a hash table read at startup.
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120 Once the samples enter the soft-core chain, the first soft-core in line
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121 takes the samples and performs some sort of audio operation, producing
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122 modified audio samples.
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123 These samples feed into the next soft-core which performs a different algorithm.
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124 As condition for functional correctness, we require the algorithm that
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125 each soft-core contains to be able to produce audio samples at the desired
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126 44khz rate, but we allow an arbitrary setup time for the soft-core to get
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127 ready.
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128 That way, a pipelined processor can take its time and fill up its pipeline
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129 completely with no worries.
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130 Once the soft-core starts producing samples, it must produce them at a
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131 rate of at least 44khz forever.
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132 If every soft-core in the chain obeys this timing condition, then the whole
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133 chain will as well, so the entire chain of soft-cores can be treated as
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134 a single big soft-core for timing purposes.
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135 Our soft-cores are just Lab 5 processors preloaded with specific audio
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136 processing algorithms.
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137 \end_layout
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138
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139 \begin_layout Standard
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140 Eventually, the samples make their way to the end of the chain of soft-cores.
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141 Every chain of soft-cores ends in a FIFO.
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142 For this project, we will have 12 separate voices.
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143 Therefore, there will be 12 soft-core chains, each with a FIFO at its end,
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144 one for each voice.
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145 Each of the 12 FIFOs leads to the mixer, which only begins operation once
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146 all 12 FIFOs are full.
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147 Because of the timing constraints we impose on our soft-cores, once every
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148 FIFO has at least one sample, all 12 will forever more be able to supply
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149 samples at 44khz.
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150 The mixer therefore waits until all 12 FIFOs have elements and then reads
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151 samples from all FIFOS at a rate of 44khz.
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152 The mixer combines the samples through simple addition and scaling, creating
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153 a single stream of sample data, which is sent back from the FPGA to the
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154 host computer where we play the stream and/or save it to a file.
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155 The mixer ensures that it outputs samples at a rate of 44khz by running
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156 everything through its own internal buffer FIFO clocked at 44khz.
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157 \end_layout
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158
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159 \end_body
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160 \end_document
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