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<li class="navelem"><a class="el" href="dir_bc0718b08fb2015b8e59c47b2805f60c.html">libraries</a></li><li class="navelem"><a class="el" href="dir_7e6ab9b017486261fe80629d442521f0.html">TransistorNoiseSource</a></li> </ul>
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<div class="title">TransistorNoiseSource.cpp</div> </div>
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</div><!--header-->
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<div class="contents">
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<div class="fragment"><div class="line"><a name="l00001"></a><span class="lineno"> 1</span> <span class="comment">/*</span></div>
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<div class="line"><a name="l00002"></a><span class="lineno"> 2</span> <span class="comment"> * Copyright (C) 2015 Southern Storm Software, Pty Ltd.</span></div>
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<div class="line"><a name="l00003"></a><span class="lineno"> 3</span> <span class="comment"> *</span></div>
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<div class="line"><a name="l00004"></a><span class="lineno"> 4</span> <span class="comment"> * Permission is hereby granted, free of charge, to any person obtaining a</span></div>
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<div class="line"><a name="l00005"></a><span class="lineno"> 5</span> <span class="comment"> * copy of this software and associated documentation files (the "Software"),</span></div>
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<div class="line"><a name="l00006"></a><span class="lineno"> 6</span> <span class="comment"> * to deal in the Software without restriction, including without limitation</span></div>
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<div class="line"><a name="l00007"></a><span class="lineno"> 7</span> <span class="comment"> * the rights to use, copy, modify, merge, publish, distribute, sublicense,</span></div>
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<div class="line"><a name="l00008"></a><span class="lineno"> 8</span> <span class="comment"> * and/or sell copies of the Software, and to permit persons to whom the</span></div>
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<div class="line"><a name="l00009"></a><span class="lineno"> 9</span> <span class="comment"> * Software is furnished to do so, subject to the following conditions:</span></div>
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<div class="line"><a name="l00010"></a><span class="lineno"> 10</span> <span class="comment"> *</span></div>
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<div class="line"><a name="l00011"></a><span class="lineno"> 11</span> <span class="comment"> * The above copyright notice and this permission notice shall be included</span></div>
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<div class="line"><a name="l00012"></a><span class="lineno"> 12</span> <span class="comment"> * in all copies or substantial portions of the Software.</span></div>
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<div class="line"><a name="l00013"></a><span class="lineno"> 13</span> <span class="comment"> *</span></div>
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<div class="line"><a name="l00014"></a><span class="lineno"> 14</span> <span class="comment"> * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS</span></div>
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<div class="line"><a name="l00015"></a><span class="lineno"> 15</span> <span class="comment"> * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,</span></div>
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<div class="line"><a name="l00016"></a><span class="lineno"> 16</span> <span class="comment"> * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE</span></div>
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<div class="line"><a name="l00017"></a><span class="lineno"> 17</span> <span class="comment"> * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER</span></div>
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<div class="line"><a name="l00018"></a><span class="lineno"> 18</span> <span class="comment"> * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING</span></div>
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<div class="line"><a name="l00019"></a><span class="lineno"> 19</span> <span class="comment"> * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER</span></div>
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<div class="line"><a name="l00020"></a><span class="lineno"> 20</span> <span class="comment"> * DEALINGS IN THE SOFTWARE.</span></div>
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<div class="line"><a name="l00021"></a><span class="lineno"> 21</span> <span class="comment"> */</span></div>
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<div class="line"><a name="l00022"></a><span class="lineno"> 22</span> </div>
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<div class="line"><a name="l00023"></a><span class="lineno"> 23</span> <span class="preprocessor">#include "TransistorNoiseSource.h"</span></div>
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<div class="line"><a name="l00024"></a><span class="lineno"> 24</span> <span class="preprocessor">#include "RNG.h"</span></div>
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<div class="line"><a name="l00025"></a><span class="lineno"> 25</span> <span class="preprocessor">#include "Crypto.h"</span></div>
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<div class="line"><a name="l00026"></a><span class="lineno"> 26</span> <span class="preprocessor">#include <Arduino.h></span></div>
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<div class="line"><a name="l00027"></a><span class="lineno"> 27</span> </div>
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<div class="line"><a name="l00078"></a><span class="lineno"> 78</span> <span class="comment">/*</span></div>
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<div class="line"><a name="l00079"></a><span class="lineno"> 79</span> <span class="comment"></span></div>
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<div class="line"><a name="l00080"></a><span class="lineno"> 80</span> <span class="comment">Theory of operation:</span></div>
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<div class="line"><a name="l00081"></a><span class="lineno"> 81</span> <span class="comment"></span></div>
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<div class="line"><a name="l00082"></a><span class="lineno"> 82</span> <span class="comment">From Rob Seward's original design we need to find the median of the input</span></div>
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<div class="line"><a name="l00083"></a><span class="lineno"> 83</span> <span class="comment">signal. That is, the threshold at which half the signal is below the</span></div>
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<div class="line"><a name="l00084"></a><span class="lineno"> 84</span> <span class="comment">threshold (a zero) and the other half is above the threshold (a one).</span></div>
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<div class="line"><a name="l00085"></a><span class="lineno"> 85</span> <span class="comment">Rob used a histogram table to find the median which is memory-intensive.</span></div>
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<div class="line"><a name="l00086"></a><span class="lineno"> 86</span> <span class="comment">We cannot afford to spend that much memory finding the median.</span></div>
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<div class="line"><a name="l00087"></a><span class="lineno"> 87</span> <span class="comment"></span></div>
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<div class="line"><a name="l00088"></a><span class="lineno"> 88</span> <span class="comment">In this implementation we divide the signal up into "buckets" of 1024</span></div>
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<div class="line"><a name="l00089"></a><span class="lineno"> 89</span> <span class="comment">samples. We pick a starting threshold and count the number of ones</span></div>
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<div class="line"><a name="l00090"></a><span class="lineno"> 90</span> <span class="comment">within the bucket. If the number of ones is between 45% to 55% of the</span></div>
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<div class="line"><a name="l00091"></a><span class="lineno"> 91</span> <span class="comment">total number of samples, then we use that threshold to convert the</span></div>
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<div class="line"><a name="l00092"></a><span class="lineno"> 92</span> <span class="comment">bucket into output bits. Otherwise we adjust the threshold up or down,</span></div>
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<div class="line"><a name="l00093"></a><span class="lineno"> 93</span> <span class="comment">discard the bucket, and try again.</span></div>
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<div class="line"><a name="l00094"></a><span class="lineno"> 94</span> <span class="comment"></span></div>
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<div class="line"><a name="l00095"></a><span class="lineno"> 95</span> <span class="comment">After a few buckets, the threshold naturally settles at the median without</span></div>
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<div class="line"><a name="l00096"></a><span class="lineno"> 96</span> <span class="comment">needing a histogram. The rest of the bucket processing can be done online</span></div>
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<div class="line"><a name="l00097"></a><span class="lineno"> 97</span> <span class="comment">with storage needed only for the debiased output bits.</span></div>
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<div class="line"><a name="l00098"></a><span class="lineno"> 98</span> <span class="comment"></span></div>
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<div class="line"><a name="l00099"></a><span class="lineno"> 99</span> <span class="comment">If the input voltage to the noise source is too low to generate noise,</span></div>
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<div class="line"><a name="l00100"></a><span class="lineno"> 100</span> <span class="comment">then the delta between the minimum and maximum samples in the bucket will</span></div>
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<div class="line"><a name="l00101"></a><span class="lineno"> 101</span> <span class="comment">be quite small. This is used to detect disconnection of the noise source.</span></div>
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<div class="line"><a name="l00102"></a><span class="lineno"> 102</span> <span class="comment">No output is generated when the noise source is disconnected.</span></div>
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<div class="line"><a name="l00103"></a><span class="lineno"> 103</span> <span class="comment"></span></div>
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<div class="line"><a name="l00104"></a><span class="lineno"> 104</span> <span class="comment">With 1024 raw input samples we get roughly 256 output bits after</span></div>
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<div class="line"><a name="l00105"></a><span class="lineno"> 105</span> <span class="comment">Von Neumann debiasing. As a further check, the output will be discarded</span></div>
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<div class="line"><a name="l00106"></a><span class="lineno"> 106</span> <span class="comment">if less than 192 bits are generated. This can happen when the noise source</span></div>
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<div class="line"><a name="l00107"></a><span class="lineno"> 107</span> <span class="comment">is connected or disconnected: only part of the bucket is valid.</span></div>
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<div class="line"><a name="l00108"></a><span class="lineno"> 108</span> <span class="comment"></span></div>
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<div class="line"><a name="l00109"></a><span class="lineno"> 109</span> <span class="comment">One of the properties of Rob's circuit design is that over time the median</span></div>
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<div class="line"><a name="l00110"></a><span class="lineno"> 110</span> <span class="comment">changes due to environmental factors and component wear. Because we adjust</span></div>
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<div class="line"><a name="l00111"></a><span class="lineno"> 111</span> <span class="comment">the threshold from bucket to bucket, it should naturally float up or down</span></div>
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<div class="line"><a name="l00112"></a><span class="lineno"> 112</span> <span class="comment">to the new median level as the circuit's properties change.</span></div>
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<div class="line"><a name="l00113"></a><span class="lineno"> 113</span> <span class="comment"></span></div>
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<div class="line"><a name="l00114"></a><span class="lineno"> 114</span> <span class="comment">*/</span></div>
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<div class="line"><a name="l00115"></a><span class="lineno"> 115</span> </div>
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<div class="line"><a name="l00116"></a><span class="lineno"> 116</span> <span class="comment">// Number of ADC values that can be generated by analogRead().</span></div>
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<div class="line"><a name="l00117"></a><span class="lineno"> 117</span> <span class="preprocessor">#define ADC_NUM 1024</span></div>
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<div class="line"><a name="l00118"></a><span class="lineno"> 118</span> <span class="preprocessor"></span></div>
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<div class="line"><a name="l00119"></a><span class="lineno"> 119</span> <span class="comment">// Number of samples to collect for a single noise "bucket".</span></div>
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<div class="line"><a name="l00120"></a><span class="lineno"> 120</span> <span class="preprocessor">#define SAMPLES_NUM 1024</span></div>
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<div class="line"><a name="l00121"></a><span class="lineno"> 121</span> <span class="preprocessor"></span></div>
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<div class="line"><a name="l00122"></a><span class="lineno"> 122</span> <span class="comment">// Calculate a percentage of the sample bucket size.</span></div>
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<div class="line"><a name="l00123"></a><span class="lineno"> 123</span> <span class="preprocessor">#define SAMPLES_PCT(num) ((int)(((long)SAMPLES_NUM) * (num) / 100L))</span></div>
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<div class="line"><a name="l00124"></a><span class="lineno"> 124</span> <span class="preprocessor"></span></div>
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<div class="line"><a name="l00125"></a><span class="lineno"> 125</span> <span class="comment">// Expected spread between the minimum and maximum ADC readings for</span></div>
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<div class="line"><a name="l00126"></a><span class="lineno"> 126</span> <span class="comment">// the noise source to be considered as operating correctly.</span></div>
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<div class="line"><a name="l00127"></a><span class="lineno"> 127</span> <span class="preprocessor">#define NOISE_SPREAD (ADC_NUM / 8)</span></div>
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<div class="line"><a name="l00128"></a><span class="lineno"> 128</span> <span class="preprocessor"></span></div>
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<div class="line"><a name="l00129"></a><span class="lineno"> 129</span> <span class="comment">// Calibration states.</span></div>
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<div class="line"><a name="l00130"></a><span class="lineno"> 130</span> <span class="preprocessor">#define NOISE_NOT_CALIBRATING 0</span></div>
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<div class="line"><a name="l00131"></a><span class="lineno"> 131</span> <span class="preprocessor"></span><span class="preprocessor">#define NOISE_CALIBRATING 1</span></div>
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<div class="line"><a name="l00132"></a><span class="lineno"> 132</span> <span class="preprocessor"></span></div>
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<div class="line"><a name="l00138"></a><span class="lineno"><a class="line" href="classTransistorNoiseSource.html#a05bab61c301a5397021048c95ca3107d"> 138</a></span> <a class="code" href="classTransistorNoiseSource.html#a05bab61c301a5397021048c95ca3107d">TransistorNoiseSource::TransistorNoiseSource</a>(uint8_t pin)</div>
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<div class="line"><a name="l00139"></a><span class="lineno"> 139</span>  : threshold(ADC_NUM / 2)</div>
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<div class="line"><a name="l00140"></a><span class="lineno"> 140</span>  , _pin(pin)</div>
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<div class="line"><a name="l00141"></a><span class="lineno"> 141</span>  , calState(NOISE_CALIBRATING)</div>
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<div class="line"><a name="l00142"></a><span class="lineno"> 142</span> {</div>
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<div class="line"><a name="l00143"></a><span class="lineno"> 143</span>  <span class="comment">// Configure the pin as an analog input with no pull-up.</span></div>
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<div class="line"><a name="l00144"></a><span class="lineno"> 144</span>  pinMode(pin, INPUT);</div>
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<div class="line"><a name="l00145"></a><span class="lineno"> 145</span>  digitalWrite(pin, LOW);</div>
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<div class="line"><a name="l00146"></a><span class="lineno"> 146</span> </div>
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<div class="line"><a name="l00147"></a><span class="lineno"> 147</span>  <span class="comment">// Start the bit collection routines.</span></div>
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<div class="line"><a name="l00148"></a><span class="lineno"> 148</span>  restart();</div>
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<div class="line"><a name="l00149"></a><span class="lineno"> 149</span> }</div>
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<div class="line"><a name="l00150"></a><span class="lineno"> 150</span> </div>
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<div class="line"><a name="l00151"></a><span class="lineno"> 151</span> TransistorNoiseSource::~TransistorNoiseSource()</div>
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<div class="line"><a name="l00152"></a><span class="lineno"> 152</span> {</div>
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<div class="line"><a name="l00153"></a><span class="lineno"> 153</span>  restart();</div>
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<div class="line"><a name="l00154"></a><span class="lineno"> 154</span> }</div>
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<div class="line"><a name="l00155"></a><span class="lineno"> 155</span> </div>
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<div class="line"><a name="l00156"></a><span class="lineno"><a class="line" href="classTransistorNoiseSource.html#a9244b327c291c737396e769da9c66af9"> 156</a></span> <span class="keywordtype">bool</span> <a class="code" href="classTransistorNoiseSource.html#a9244b327c291c737396e769da9c66af9">TransistorNoiseSource::calibrating</a>()<span class="keyword"> const</span></div>
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<div class="line"><a name="l00157"></a><span class="lineno"> 157</span> <span class="keyword"></span>{</div>
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<div class="line"><a name="l00158"></a><span class="lineno"> 158</span>  <span class="keywordflow">return</span> calState != NOISE_NOT_CALIBRATING;</div>
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<div class="line"><a name="l00159"></a><span class="lineno"> 159</span> }</div>
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<div class="line"><a name="l00160"></a><span class="lineno"> 160</span> </div>
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<div class="line"><a name="l00161"></a><span class="lineno"><a class="line" href="classTransistorNoiseSource.html#add25c6a14b0506bc30ca781f2d923917"> 161</a></span> <span class="keywordtype">void</span> <a class="code" href="classTransistorNoiseSource.html#add25c6a14b0506bc30ca781f2d923917">TransistorNoiseSource::stir</a>()</div>
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<div class="line"><a name="l00162"></a><span class="lineno"> 162</span> {</div>
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<div class="line"><a name="l00163"></a><span class="lineno"> 163</span>  <span class="comment">// Keep track of the minimum and maximum while generating data</span></div>
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<div class="line"><a name="l00164"></a><span class="lineno"> 164</span>  <span class="comment">// so that we can detect when the input voltage falls too low</span></div>
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<div class="line"><a name="l00165"></a><span class="lineno"> 165</span>  <span class="comment">// for the circuit to generate noise.</span></div>
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<div class="line"><a name="l00166"></a><span class="lineno"> 166</span>  <span class="keywordtype">int</span> value = analogRead(_pin);</div>
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<div class="line"><a name="l00167"></a><span class="lineno"> 167</span>  <span class="keywordflow">if</span> (value < minValue)</div>
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<div class="line"><a name="l00168"></a><span class="lineno"> 168</span>  minValue = value;</div>
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<div class="line"><a name="l00169"></a><span class="lineno"> 169</span>  <span class="keywordflow">if</span> (value > maxValue)</div>
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<div class="line"><a name="l00170"></a><span class="lineno"> 170</span>  maxValue = value;</div>
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<div class="line"><a name="l00171"></a><span class="lineno"> 171</span> </div>
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<div class="line"><a name="l00172"></a><span class="lineno"> 172</span>  <span class="comment">// Collect two bits of input and remove bias using the Von Neumann method.</span></div>
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<div class="line"><a name="l00173"></a><span class="lineno"> 173</span>  <span class="comment">// If both bits are the same, then discard both. Otherwise choose one</span></div>
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<div class="line"><a name="l00174"></a><span class="lineno"> 174</span>  <span class="comment">// of the bits and output that one. We have to do this carefully so that</span></div>
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<div class="line"><a name="l00175"></a><span class="lineno"> 175</span>  <span class="comment">// instruction timing does not reveal the value of the bit that is chosen.</span></div>
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<div class="line"><a name="l00176"></a><span class="lineno"> 176</span>  uint8_t bit = ((threshold - value) >> 15) & 1; <span class="comment">// Subtract and extract sign.</span></div>
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<div class="line"><a name="l00177"></a><span class="lineno"> 177</span>  <span class="keywordflow">if</span> (count & 1) {</div>
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<div class="line"><a name="l00178"></a><span class="lineno"> 178</span>  <span class="keywordflow">if</span> (prevBit ^ bit) {</div>
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<div class="line"><a name="l00179"></a><span class="lineno"> 179</span>  <span class="comment">// The bits are different: add the new bit to the buffer.</span></div>
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<div class="line"><a name="l00180"></a><span class="lineno"> 180</span>  <span class="keywordflow">if</span> (posn < <span class="keyword">sizeof</span>(buffer)) {</div>
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<div class="line"><a name="l00181"></a><span class="lineno"> 181</span>  buffer[posn] = (buffer[posn] << 1) | bit;</div>
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<div class="line"><a name="l00182"></a><span class="lineno"> 182</span>  <span class="keywordflow">if</span> (++bitNum >= 8) {</div>
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<div class="line"><a name="l00183"></a><span class="lineno"> 183</span>  ++posn;</div>
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<div class="line"><a name="l00184"></a><span class="lineno"> 184</span>  bitNum = 0;</div>
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<div class="line"><a name="l00185"></a><span class="lineno"> 185</span>  }</div>
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<div class="line"><a name="l00186"></a><span class="lineno"> 186</span>  }</div>
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<div class="line"><a name="l00187"></a><span class="lineno"> 187</span>  }</div>
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<div class="line"><a name="l00188"></a><span class="lineno"> 188</span>  } <span class="keywordflow">else</span> {</div>
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<div class="line"><a name="l00189"></a><span class="lineno"> 189</span>  prevBit = bit;</div>
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<div class="line"><a name="l00190"></a><span class="lineno"> 190</span>  }</div>
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<div class="line"><a name="l00191"></a><span class="lineno"> 191</span> </div>
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<div class="line"><a name="l00192"></a><span class="lineno"> 192</span>  <span class="comment">// Keep a count of the number of raw 1 bits.</span></div>
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<div class="line"><a name="l00193"></a><span class="lineno"> 193</span>  ones += bit;</div>
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<div class="line"><a name="l00194"></a><span class="lineno"> 194</span> </div>
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<div class="line"><a name="l00195"></a><span class="lineno"> 195</span>  <span class="comment">// Bail out if we haven't collected enough samples for a full bucket yet.</span></div>
|
|
<div class="line"><a name="l00196"></a><span class="lineno"> 196</span>  <span class="keywordflow">if</span> (++count < SAMPLES_NUM)</div>
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<div class="line"><a name="l00197"></a><span class="lineno"> 197</span>  <span class="keywordflow">return</span>;</div>
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<div class="line"><a name="l00198"></a><span class="lineno"> 198</span> </div>
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|
<div class="line"><a name="l00199"></a><span class="lineno"> 199</span>  <span class="comment">// If the maximum minus the minimum is too small, then there probably</span></div>
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|
<div class="line"><a name="l00200"></a><span class="lineno"> 200</span>  <span class="comment">// is no signal or the input voltage is insufficient to generate noise.</span></div>
|
|
<div class="line"><a name="l00201"></a><span class="lineno"> 201</span>  <span class="comment">// Discard the entire bucket and return to calibration.</span></div>
|
|
<div class="line"><a name="l00202"></a><span class="lineno"> 202</span>  <span class="keywordflow">if</span> ((maxValue - minValue) < NOISE_SPREAD) {</div>
|
|
<div class="line"><a name="l00203"></a><span class="lineno"> 203</span>  restart();</div>
|
|
<div class="line"><a name="l00204"></a><span class="lineno"> 204</span>  calState = NOISE_CALIBRATING;</div>
|
|
<div class="line"><a name="l00205"></a><span class="lineno"> 205</span>  threshold = ADC_NUM / 2; <span class="comment">// Reacquire threshold when the signal returns.</span></div>
|
|
<div class="line"><a name="l00206"></a><span class="lineno"> 206</span>  <span class="keywordflow">return</span>;</div>
|
|
<div class="line"><a name="l00207"></a><span class="lineno"> 207</span>  }</div>
|
|
<div class="line"><a name="l00208"></a><span class="lineno"> 208</span> </div>
|
|
<div class="line"><a name="l00209"></a><span class="lineno"> 209</span>  <span class="comment">// If the number of 1's is between 45% and 55% of the total count,</span></div>
|
|
<div class="line"><a name="l00210"></a><span class="lineno"> 210</span>  <span class="comment">// then we have a good bucket. The threshold is at an appropriate level.</span></div>
|
|
<div class="line"><a name="l00211"></a><span class="lineno"> 211</span>  <span class="keywordflow">if</span> (ones >= SAMPLES_PCT(45) && ones <= SAMPLES_PCT(55)) {</div>
|
|
<div class="line"><a name="l00212"></a><span class="lineno"> 212</span>  <span class="keywordflow">if</span> (posn >= (<span class="keyword">sizeof</span>(buffer) * 3 / 4)) {</div>
|
|
<div class="line"><a name="l00213"></a><span class="lineno"> 213</span>  <span class="comment">// The buffer is at least three-quarters full of debiased bits</span></div>
|
|
<div class="line"><a name="l00214"></a><span class="lineno"> 214</span>  <span class="comment">// so pass them onto output(). There may be less bits if we</span></div>
|
|
<div class="line"><a name="l00215"></a><span class="lineno"> 215</span>  <span class="comment">// lost or gained the signal half-way through the bucket.</span></div>
|
|
<div class="line"><a name="l00216"></a><span class="lineno"> 216</span>  <span class="comment">// Credit 4 bits of entropy for every 8 bits of output.</span></div>
|
|
<div class="line"><a name="l00217"></a><span class="lineno"> 217</span>  <a class="code" href="classNoiseSource.html#a1af7449a5ae4a8acd34ac218c9eec6c1">output</a>(buffer, posn, posn * 4);</div>
|
|
<div class="line"><a name="l00218"></a><span class="lineno"> 218</span>  }</div>
|
|
<div class="line"><a name="l00219"></a><span class="lineno"> 219</span>  restart();</div>
|
|
<div class="line"><a name="l00220"></a><span class="lineno"> 220</span>  calState = NOISE_NOT_CALIBRATING;</div>
|
|
<div class="line"><a name="l00221"></a><span class="lineno"> 221</span>  <span class="keywordflow">return</span>;</div>
|
|
<div class="line"><a name="l00222"></a><span class="lineno"> 222</span>  }</div>
|
|
<div class="line"><a name="l00223"></a><span class="lineno"> 223</span> </div>
|
|
<div class="line"><a name="l00224"></a><span class="lineno"> 224</span>  <span class="comment">// The threshold is not close enough to the mid-point of the signal.</span></div>
|
|
<div class="line"><a name="l00225"></a><span class="lineno"> 225</span>  <span class="comment">// Adjust the threshold, discard the bucket, and try again.</span></div>
|
|
<div class="line"><a name="l00226"></a><span class="lineno"> 226</span>  <span class="keywordflow">if</span> (ones < SAMPLES_PCT(25) || ones > SAMPLES_PCT(75)) {</div>
|
|
<div class="line"><a name="l00227"></a><span class="lineno"> 227</span>  <span class="comment">// We are a long way away from the mid-point, so move the threshold</span></div>
|
|
<div class="line"><a name="l00228"></a><span class="lineno"> 228</span>  <span class="comment">// by a large amount based on the delta to get closer quicker.</span></div>
|
|
<div class="line"><a name="l00229"></a><span class="lineno"> 229</span>  threshold -= (SAMPLES_PCT(50) - ones) / 8;</div>
|
|
<div class="line"><a name="l00230"></a><span class="lineno"> 230</span>  } <span class="keywordflow">else</span> <span class="keywordflow">if</span> (ones < SAMPLES_PCT(50)) {</div>
|
|
<div class="line"><a name="l00231"></a><span class="lineno"> 231</span>  <span class="comment">// Not enough ones so move the threshold down a bit.</span></div>
|
|
<div class="line"><a name="l00232"></a><span class="lineno"> 232</span>  --threshold;</div>
|
|
<div class="line"><a name="l00233"></a><span class="lineno"> 233</span>  } <span class="keywordflow">else</span> {</div>
|
|
<div class="line"><a name="l00234"></a><span class="lineno"> 234</span>  <span class="comment">// Too many ones so move the threshold up a bit.</span></div>
|
|
<div class="line"><a name="l00235"></a><span class="lineno"> 235</span>  ++threshold;</div>
|
|
<div class="line"><a name="l00236"></a><span class="lineno"> 236</span>  }</div>
|
|
<div class="line"><a name="l00237"></a><span class="lineno"> 237</span>  <span class="keywordflow">if</span> (threshold < 0)</div>
|
|
<div class="line"><a name="l00238"></a><span class="lineno"> 238</span>  threshold = 0;</div>
|
|
<div class="line"><a name="l00239"></a><span class="lineno"> 239</span>  <span class="keywordflow">else</span> <span class="keywordflow">if</span> (threshold >= ADC_NUM)</div>
|
|
<div class="line"><a name="l00240"></a><span class="lineno"> 240</span>  threshold = ADC_NUM - 1;</div>
|
|
<div class="line"><a name="l00241"></a><span class="lineno"> 241</span>  restart();</div>
|
|
<div class="line"><a name="l00242"></a><span class="lineno"> 242</span>  calState = NOISE_CALIBRATING;</div>
|
|
<div class="line"><a name="l00243"></a><span class="lineno"> 243</span> }</div>
|
|
<div class="line"><a name="l00244"></a><span class="lineno"> 244</span> </div>
|
|
<div class="line"><a name="l00248"></a><span class="lineno"> 248</span> <span class="keywordtype">void</span> TransistorNoiseSource::restart()</div>
|
|
<div class="line"><a name="l00249"></a><span class="lineno"> 249</span> {</div>
|
|
<div class="line"><a name="l00250"></a><span class="lineno"> 250</span>  clean(buffer);</div>
|
|
<div class="line"><a name="l00251"></a><span class="lineno"> 251</span>  prevBit = 0;</div>
|
|
<div class="line"><a name="l00252"></a><span class="lineno"> 252</span>  posn = 0;</div>
|
|
<div class="line"><a name="l00253"></a><span class="lineno"> 253</span>  bitNum = 0;</div>
|
|
<div class="line"><a name="l00254"></a><span class="lineno"> 254</span>  minValue = ADC_NUM - 1;</div>
|
|
<div class="line"><a name="l00255"></a><span class="lineno"> 255</span>  maxValue = 0;</div>
|
|
<div class="line"><a name="l00256"></a><span class="lineno"> 256</span>  count = 0;</div>
|
|
<div class="line"><a name="l00257"></a><span class="lineno"> 257</span>  ones = 0;</div>
|
|
<div class="line"><a name="l00258"></a><span class="lineno"> 258</span> }</div>
|
|
<div class="ttc" id="classTransistorNoiseSource_html_a9244b327c291c737396e769da9c66af9"><div class="ttname"><a href="classTransistorNoiseSource.html#a9244b327c291c737396e769da9c66af9">TransistorNoiseSource::calibrating</a></div><div class="ttdeci">bool calibrating() const </div><div class="ttdoc">Determine if the noise source is still calibrating itself. </div><div class="ttdef"><b>Definition:</b> <a href="TransistorNoiseSource_8cpp_source.html#l00156">TransistorNoiseSource.cpp:156</a></div></div>
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<div class="ttc" id="classNoiseSource_html_a1af7449a5ae4a8acd34ac218c9eec6c1"><div class="ttname"><a href="classNoiseSource.html#a1af7449a5ae4a8acd34ac218c9eec6c1">NoiseSource::output</a></div><div class="ttdeci">virtual void output(const uint8_t *data, size_t len, unsigned int credit)</div><div class="ttdoc">Called from subclasses to output noise to the global random number pool. </div><div class="ttdef"><b>Definition:</b> <a href="NoiseSource_8cpp_source.html#l00117">NoiseSource.cpp:117</a></div></div>
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<div class="ttc" id="classTransistorNoiseSource_html_a05bab61c301a5397021048c95ca3107d"><div class="ttname"><a href="classTransistorNoiseSource.html#a05bab61c301a5397021048c95ca3107d">TransistorNoiseSource::TransistorNoiseSource</a></div><div class="ttdeci">TransistorNoiseSource(uint8_t pin)</div><div class="ttdoc">Constructs a new transitor-based noise source handler. </div><div class="ttdef"><b>Definition:</b> <a href="TransistorNoiseSource_8cpp_source.html#l00138">TransistorNoiseSource.cpp:138</a></div></div>
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<div class="ttc" id="classTransistorNoiseSource_html_add25c6a14b0506bc30ca781f2d923917"><div class="ttname"><a href="classTransistorNoiseSource.html#add25c6a14b0506bc30ca781f2d923917">TransistorNoiseSource::stir</a></div><div class="ttdeci">void stir()</div><div class="ttdoc">Stirs entropy from this noise source into the global random number pool. </div><div class="ttdef"><b>Definition:</b> <a href="TransistorNoiseSource_8cpp_source.html#l00161">TransistorNoiseSource.cpp:161</a></div></div>
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